This series enables Linux guests running on Hyper-V on ARM64
hardware. New ARM64-specific code in arch/arm64/hyperv initializes
Hyper-V and its hypercall mechanism. Existing architecture
independent drivers for Hyper-V's VMbus and synthetic devices just
work when built for ARM64. Hyper-V code is built and included in
the image and modules only if CONFIG_HYPERV is enabled.
The five patches are organized as follows:
1) Add definitions and functions for making Hyper-V hypercalls
and getting/setting virtual processor registers provided by
Hyper-V
2) Add the function needed by the arch independent VMbus driver
for reporting a panic to Hyper-V.
3) Add Hyper-V initialization code and utility functions that
report Hyper-v status.
4) Export screen_info so it may be used by the Hyper-V frame buffer
driver built as a module. It is already exported for x86,
powerpc, and alpha architectures.
5) Make CONFIG_HYPERV selectable on ARM64 in addition to x86/x64.
Hyper-V on ARM64 runs with a 4 Kbyte page size, but allows guests
with 4K/16K/64K page size. Linux guests with this patch series
work with all three supported ARM64 page sizes.
The Hyper-V vPCI driver at drivers/pci/host/pci-hyperv.c has
x86/x64-specific code and is not being built for ARM64. Enabling
Hyper-V vPCI devices on ARM64 is in progress via a separate set
of patches.
This patch set is based on the linux-next20210720 code tree.
Changes in v11:
* Drop the previous Patch 1 as the fixes have already been
separately accepted upstream.
* Drop the previous Patch 3 for enabling Hyper-V enlightened
clocks/timers. Hyper-V is now offering the full ARM64
architectural Generic Timer in guest VMs, so the existing
arch_arch_timer.c driver just works. [Mark Rutland, Marc
Zyngier]
* Simplified the previous Patch 4 and Patch 5 (now Patch 2 and 3)
by sharing more code between the x86 and ARM64 architectures.
* Combined hyperv_early_init() and hyperv_init() into a single
initialization function that runs as an early_initcall. This
is possible because the Hyper-V enlightened clocks/timers
no longer need to be initialized early in the boot sequence.
Changes in v10:
* Drop previous Patch 1 for SMCCC v1.2 HVC calls in favor of
Sudeep Holla's patch [Mark Rutland]
* Use new helper functions in 5.13 for checking Hyper-V hypercall
return status
* Set up per-CPU hypercall argument page that is now used by the
Hyper-V balloon driver
* Rebase on 5.13-RC1
Changes in v9:
* Added Patch 1 to enable making an SMCCC compliant hypercall
that returns results in other than registers X0 thru X3, per
version 1.2 and later of the SMCCC spec.
* Using the ability to return results in registers X6 and X7,
converted hv_get_vpreg_128() to use a "fast" hypercall that
passes inputs and outputs in registers, and in doing so eliminated
a lot of memory allocation complexity.
* Cleaned up some extra blank lines and use of spaces in aligning
local variables. [Sunil Muthuswamy]
* Based on discussion about future directions, reverted the
population of hv_vp_index array to use a cpuhp state instead
of a hypercall, which is like it was in v7 and earlier.
Changes in v8:
* Removed a lot of code based on refactoring the boundary between
arch independent and arch dependent code for Hyper-V, per comments
from Arnd Bergmann. The removed code was either duplicated on
the x86 side, or has been folded into architecture independent
code as not really being architecture dependent.
* Added config dependency on !CONFIG_CPU_BIG_ENDIAN [Arnd Bergmann]
* Reworked the approach to Hyper-V initialization. The functionality
is the same, but is now structured like the Xen code with an early
init function called in setup_arch() and an early initcall to
finish the initialization. [Arnd Bergmann]
Changes in v7:
* Separately upstreamed split of hyperv-tlfs.h into arch dependent
and independent versions. In this patch set, update the ARM64
hyperv-tlfs.h to include architecture independent definitions.
This approach eliminates a lot of lines of otherwise duplicated
code on the ARM64 side.
* Break ARM64 mshyperv.h into smaller pieces. Have an initial
baseline, and add code along with patches for a particular
functional area. [Marc Zyngier]
* In mshyperv.h, use static inline functions instead of #defines
where possible. [Arnd Bergmann]
* Use VMbus INTID obtained from ACPI DSDT instead of hardcoding.
The STIMER INTID is still hardcoded because it is needed
before Linux has initialized the ACPI subsystem, so it can't
be obtained from the DSDT. Wedging it into the GTDT seems
dubious, so was not done. [Marc Zyngier]
* Update Hyper-V page size allocation functions to use
alloc_page() if PAGE_SIZE == HV_HYP_PAGE_SIZE [Arnd
Bergmann]
* Various other minor changes based on feedback and to rebase
to latest linux-next [Marc Zyngier and Arnd Bergmann]
Changes in v6:
* Use SMCCC hypercall interface instead of direct invocation
of HVC instruction and the Hyper-V hypercall interface
[Marc Zyngier]
* Reimplemented functions to alloc/free Hyper-V size pages
using kmalloc/kfree since kmalloc now guarantees alignment of
power of 2 size allocations [Marc Zyngier]
* Export screen_info in arm64 architecture so it can be used
by the Hyper-V buffer driver built as a module
* Renamed source file arch/arm64/hyperv/hv_init.c to hv_core.c
to better reflect its content
* Fixed the bit position of certain feature flags presented by
Hyper-V to the guest. The bit positions on ARM64 don't match
the position on x86 like originally thought.
* Minor fixups to rebase to 5.6-rc5 linux-next
Changes in v5:
* Minor fixups to rebase to 5.4-rc1 linux-next
Changes in v4:
* Moved clock-related code into an architecture independent
Hyper-V clocksource driver that is already upstream. Clock
related code is removed from this patch set except for the
ARM64 specific interrupt handler. [Marc Zyngier]
* Separately upstreamed the split of mshyperv.h into arch independent
and arch dependent portions. The arch independent portion has been
removed from this patch set.
* Divided patch #2 of the series into multiple smaller patches
[Marc Zyngier]
* Changed a dozen or so smaller things based on feedback
[Marc Zyngier, Will Deacon]
* Added functions to alloc/free Hyper-V size pages for use by
drivers for Hyper-V synthetic devices when updated to not assume
guest page size and Hyper-v page size are the same
Changes in v3:
* Added initialization of hv_vp_index array like was recently
added on x86 branch [KY Srinivasan]
* Changed Hyper-V ARM64 register symbols to be all uppercase
instead of mixed case [KY Srinivasan]
* Separated mshyperv.h into two files, one architecture
independent and one architecture dependent. After this code
is upstream, will make changes to the x86 code to use the
architecture independent file and remove duplication. And
once we have a multi-architecture Hyper-V TLFS, will do a
separate patch to split hyperv-tlfs.h in the same way.
[KY Srinivasan]
* Minor tweaks to rebase to latest linux-next code
Changes in v2:
* Removed patch to implement slow_virt_to_phys() on ARM64.
Use of slow_virt_to_phys() in arch independent Hyper-V
drivers has been eliminated by commit 6ba34171bcbd
("Drivers: hv: vmbus: Remove use of slow_virt_to_phys()")
* Minor tweaks to rebase to latest linux-next code
Michael Kelley (5):
arm64: hyperv: Add Hyper-V hypercall and register access utilities
arm64: hyperv: Add panic handler
arm64: hyperv: Initialize hypervisor on boot
arm64: efi: Export screen_info
Drivers: hv: Enable Hyper-V code to be built on ARM64
MAINTAINERS | 3 +
arch/arm64/Kbuild | 1 +
arch/arm64/hyperv/Makefile | 2 +
arch/arm64/hyperv/hv_core.c | 181 +++++++++++++++++++++++++++++++++++
arch/arm64/hyperv/mshyperv.c | 83 ++++++++++++++++
arch/arm64/include/asm/hyperv-tlfs.h | 69 +++++++++++++
arch/arm64/include/asm/mshyperv.h | 54 +++++++++++
arch/arm64/kernel/efi.c | 1 +
drivers/hv/Kconfig | 5 +-
9 files changed, 397 insertions(+), 2 deletions(-)
create mode 100644 arch/arm64/hyperv/Makefile
create mode 100644 arch/arm64/hyperv/hv_core.c
create mode 100644 arch/arm64/hyperv/mshyperv.c
create mode 100644 arch/arm64/include/asm/hyperv-tlfs.h
create mode 100644 arch/arm64/include/asm/mshyperv.h
--
1.8.3.1
Add a function to inform Hyper-V about a guest panic.
This code is built only when CONFIG_HYPERV is enabled.
Signed-off-by: Michael Kelley <[email protected]>
---
arch/arm64/hyperv/hv_core.c | 52 +++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 52 insertions(+)
diff --git a/arch/arm64/hyperv/hv_core.c b/arch/arm64/hyperv/hv_core.c
index 4c5dc0f..b54c347 100644
--- a/arch/arm64/hyperv/hv_core.c
+++ b/arch/arm64/hyperv/hv_core.c
@@ -127,3 +127,55 @@ u64 hv_get_vpreg(u32 msr)
return output.as64.low;
}
EXPORT_SYMBOL_GPL(hv_get_vpreg);
+
+/*
+ * hyperv_report_panic - report a panic to Hyper-V. This function uses
+ * the older version of the Hyper-V interface that admittedly doesn't
+ * pass enough information to be useful beyond just recording the
+ * occurrence of a panic. The parallel hv_kmsg_dump() uses the
+ * new interface that allows reporting 4 Kbytes of data, which is much
+ * more useful. Hyper-V on ARM64 always supports the newer interface, but
+ * we retain support for the older version because the sysadmin is allowed
+ * to disable the newer version via sysctl in case of information security
+ * concerns about the more verbose version.
+ */
+void hyperv_report_panic(struct pt_regs *regs, long err, bool in_die)
+{
+ static bool panic_reported;
+ u64 guest_id;
+
+ /* Don't report a panic to Hyper-V if we're not going to panic */
+ if (in_die && !panic_on_oops)
+ return;
+
+ /*
+ * We prefer to report panic on 'die' chain as we have proper
+ * registers to report, but if we miss it (e.g. on BUG()) we need
+ * to report it on 'panic'.
+ *
+ * Calling code in the 'die' and 'panic' paths ensures that only
+ * one CPU is running this code, so no atomicity is needed.
+ */
+ if (panic_reported)
+ return;
+ panic_reported = true;
+
+ guest_id = hv_get_vpreg(HV_REGISTER_GUEST_OSID);
+
+ /*
+ * Hyper-V provides the ability to store only 5 values.
+ * Pick the passed in error value, the guest_id, the PC,
+ * and the SP.
+ */
+ hv_set_vpreg(HV_REGISTER_CRASH_P0, err);
+ hv_set_vpreg(HV_REGISTER_CRASH_P1, guest_id);
+ hv_set_vpreg(HV_REGISTER_CRASH_P2, regs->pc);
+ hv_set_vpreg(HV_REGISTER_CRASH_P3, regs->sp);
+ hv_set_vpreg(HV_REGISTER_CRASH_P4, 0);
+
+ /*
+ * Let Hyper-V know there is crash data available
+ */
+ hv_set_vpreg(HV_REGISTER_CRASH_CTL, HV_CRASH_CTL_CRASH_NOTIFY);
+}
+EXPORT_SYMBOL_GPL(hyperv_report_panic);
--
1.8.3.1
Add ARM64-specific code to initialize the Hyper-V
hypervisor when booting as a guest VM.
This code is built only when CONFIG_HYPERV is enabled.
Signed-off-by: Michael Kelley <[email protected]>
---
arch/arm64/hyperv/Makefile | 2 +-
arch/arm64/hyperv/mshyperv.c | 83 ++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 84 insertions(+), 1 deletion(-)
create mode 100644 arch/arm64/hyperv/mshyperv.c
diff --git a/arch/arm64/hyperv/Makefile b/arch/arm64/hyperv/Makefile
index 1697d30..87c31c0 100644
--- a/arch/arm64/hyperv/Makefile
+++ b/arch/arm64/hyperv/Makefile
@@ -1,2 +1,2 @@
# SPDX-License-Identifier: GPL-2.0
-obj-y := hv_core.o
+obj-y := hv_core.o mshyperv.o
diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
new file mode 100644
index 0000000..2811fd0
--- /dev/null
+++ b/arch/arm64/hyperv/mshyperv.c
@@ -0,0 +1,83 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Core routines for interacting with Microsoft's Hyper-V hypervisor,
+ * including hypervisor initialization.
+ *
+ * Copyright (C) 2021, Microsoft, Inc.
+ *
+ * Author : Michael Kelley <[email protected]>
+ */
+
+#include <linux/types.h>
+#include <linux/acpi.h>
+#include <linux/export.h>
+#include <linux/errno.h>
+#include <linux/version.h>
+#include <linux/cpuhotplug.h>
+#include <asm/mshyperv.h>
+
+static bool hyperv_initialized;
+
+static int __init hyperv_init(void)
+{
+ struct hv_get_vp_registers_output result;
+ u32 a, b, c, d;
+ u64 guest_id;
+ int ret;
+
+ /*
+ * If we're in a VM on Hyper-V, the ACPI hypervisor_id field will
+ * have the string "MsHyperV".
+ */
+ if (strncmp((char *)&acpi_gbl_FADT.hypervisor_id, "MsHyperV", 8))
+ return -EINVAL;
+
+ /* Setup the guest ID */
+ guest_id = generate_guest_id(0, LINUX_VERSION_CODE, 0);
+ hv_set_vpreg(HV_REGISTER_GUEST_OSID, guest_id);
+
+ /* Get the features and hints from Hyper-V */
+ hv_get_vpreg_128(HV_REGISTER_FEATURES, &result);
+ ms_hyperv.features = result.as32.a;
+ ms_hyperv.priv_high = result.as32.b;
+ ms_hyperv.misc_features = result.as32.c;
+
+ hv_get_vpreg_128(HV_REGISTER_ENLIGHTENMENTS, &result);
+ ms_hyperv.hints = result.as32.a;
+
+ pr_info("Hyper-V: privilege flags low 0x%x, high 0x%x, hints 0x%x, misc 0x%x\n",
+ ms_hyperv.features, ms_hyperv.priv_high, ms_hyperv.hints,
+ ms_hyperv.misc_features);
+
+ /* Get information about the Hyper-V host version */
+ hv_get_vpreg_128(HV_REGISTER_HYPERVISOR_VERSION, &result);
+ a = result.as32.a;
+ b = result.as32.b;
+ c = result.as32.c;
+ d = result.as32.d;
+ pr_info("Hyper-V: Host Build %d.%d.%d.%d-%d-%d\n",
+ b >> 16, b & 0xFFFF, a, d & 0xFFFFFF, c, d >> 24);
+
+ ret = hv_common_init();
+ if (ret)
+ return ret;
+
+ ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "arm64/hyperv_init:online",
+ hv_common_cpu_init, hv_common_cpu_die);
+ if (ret < 0) {
+ hv_common_free();
+ return ret;
+ }
+
+ hyperv_initialized = true;
+ return 0;
+}
+
+early_initcall(hyperv_init);
+
+bool hv_is_hyperv_initialized(void)
+{
+ return hyperv_initialized;
+}
+EXPORT_SYMBOL_GPL(hv_is_hyperv_initialized);
--
1.8.3.1
The Hyper-V frame buffer driver may be built as a module, and
it needs access to screen_info. So export screen_info.
Signed-off-by: Michael Kelley <[email protected]>
Acked-by: Ard Biesheuvel <[email protected]>
---
arch/arm64/kernel/efi.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
index fa02efb..e1be6c4 100644
--- a/arch/arm64/kernel/efi.c
+++ b/arch/arm64/kernel/efi.c
@@ -55,6 +55,7 @@ static __init pteval_t create_mapping_protection(efi_memory_desc_t *md)
/* we will fill this structure from the stub, so don't put it in .bss */
struct screen_info screen_info __section(".data");
+EXPORT_SYMBOL(screen_info);
int __init efi_create_mapping(struct mm_struct *mm, efi_memory_desc_t *md)
{
--
1.8.3.1
hyperv-tlfs.h defines Hyper-V interfaces from the Hyper-V Top Level
Functional Spec (TLFS), and #includes the architecture-independent
part of hyperv-tlfs.h in include/asm-generic. The published TLFS
is distinctly oriented to x86/x64, so the ARM64-specific
hyperv-tlfs.h includes information for ARM64 that is not yet formally
published. The TLFS is available here:
docs.microsoft.com/en-us/virtualization/hyper-v-on-windows/reference/tlfs
mshyperv.h defines Linux-specific structures and routines for
interacting with Hyper-V on ARM64, and #includes the architecture-
independent part of mshyperv.h in include/asm-generic.
Use these definitions to provide utility functions to make
Hyper-V hypercalls and to get and set Hyper-V provided
registers associated with a virtual processor.
Signed-off-by: Michael Kelley <[email protected]>
Reviewed-by: Sunil Muthuswamy <[email protected]>
---
MAINTAINERS | 3 +
arch/arm64/Kbuild | 1 +
arch/arm64/hyperv/Makefile | 2 +
arch/arm64/hyperv/hv_core.c | 129 +++++++++++++++++++++++++++++++++++
arch/arm64/include/asm/hyperv-tlfs.h | 69 +++++++++++++++++++
arch/arm64/include/asm/mshyperv.h | 54 +++++++++++++++
6 files changed, 258 insertions(+)
create mode 100644 arch/arm64/hyperv/Makefile
create mode 100644 arch/arm64/hyperv/hv_core.c
create mode 100644 arch/arm64/include/asm/hyperv-tlfs.h
create mode 100644 arch/arm64/include/asm/mshyperv.h
diff --git a/MAINTAINERS b/MAINTAINERS
index 6993219..8f6f429 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -8608,6 +8608,9 @@ T: git git://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux.git
F: Documentation/ABI/stable/sysfs-bus-vmbus
F: Documentation/ABI/testing/debugfs-hyperv
F: Documentation/networking/device_drivers/ethernet/microsoft/netvsc.rst
+F: arch/arm64/hyperv
+F: arch/arm64/include/asm/hyperv-tlfs.h
+F: arch/arm64/include/asm/mshyperv.h
F: arch/x86/hyperv
F: arch/x86/include/asm/hyperv-tlfs.h
F: arch/x86/include/asm/mshyperv.h
diff --git a/arch/arm64/Kbuild b/arch/arm64/Kbuild
index 7b393cf..ea7ab4c 100644
--- a/arch/arm64/Kbuild
+++ b/arch/arm64/Kbuild
@@ -2,4 +2,5 @@
obj-y += kernel/ mm/ net/
obj-$(CONFIG_KVM) += kvm/
obj-$(CONFIG_XEN) += xen/
+obj-$(subst m,y,$(CONFIG_HYPERV)) += hyperv/
obj-$(CONFIG_CRYPTO) += crypto/
diff --git a/arch/arm64/hyperv/Makefile b/arch/arm64/hyperv/Makefile
new file mode 100644
index 0000000..1697d30
--- /dev/null
+++ b/arch/arm64/hyperv/Makefile
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0
+obj-y := hv_core.o
diff --git a/arch/arm64/hyperv/hv_core.c b/arch/arm64/hyperv/hv_core.c
new file mode 100644
index 0000000..4c5dc0f
--- /dev/null
+++ b/arch/arm64/hyperv/hv_core.c
@@ -0,0 +1,129 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Low level utility routines for interacting with Hyper-V.
+ *
+ * Copyright (C) 2021, Microsoft, Inc.
+ *
+ * Author : Michael Kelley <[email protected]>
+ */
+
+#include <linux/types.h>
+#include <linux/export.h>
+#include <linux/mm.h>
+#include <linux/hyperv.h>
+#include <linux/arm-smccc.h>
+#include <linux/module.h>
+#include <asm-generic/bug.h>
+#include <asm/hyperv-tlfs.h>
+#include <asm/mshyperv.h>
+
+/*
+ * hv_do_hypercall- Invoke the specified hypercall
+ */
+u64 hv_do_hypercall(u64 control, void *input, void *output)
+{
+ struct arm_smccc_res res;
+ u64 input_address;
+ u64 output_address;
+
+ input_address = input ? virt_to_phys(input) : 0;
+ output_address = output ? virt_to_phys(output) : 0;
+
+ arm_smccc_1_1_hvc(HV_FUNC_ID, control,
+ input_address, output_address, &res);
+ return res.a0;
+}
+EXPORT_SYMBOL_GPL(hv_do_hypercall);
+
+/*
+ * hv_do_fast_hypercall8 -- Invoke the specified hypercall
+ * with arguments in registers instead of physical memory.
+ * Avoids the overhead of virt_to_phys for simple hypercalls.
+ */
+
+u64 hv_do_fast_hypercall8(u16 code, u64 input)
+{
+ struct arm_smccc_res res;
+ u64 control;
+
+ control = (u64)code | HV_HYPERCALL_FAST_BIT;
+
+ arm_smccc_1_1_hvc(HV_FUNC_ID, control, input, &res);
+ return res.a0;
+}
+EXPORT_SYMBOL_GPL(hv_do_fast_hypercall8);
+
+/*
+ * Set a single VP register to a 64-bit value.
+ */
+void hv_set_vpreg(u32 msr, u64 value)
+{
+ struct arm_smccc_res res;
+
+ arm_smccc_1_1_hvc(HV_FUNC_ID,
+ HVCALL_SET_VP_REGISTERS | HV_HYPERCALL_FAST_BIT |
+ HV_HYPERCALL_REP_COMP_1,
+ HV_PARTITION_ID_SELF,
+ HV_VP_INDEX_SELF,
+ msr,
+ 0,
+ value,
+ 0,
+ &res);
+
+ /*
+ * Something is fundamentally broken in the hypervisor if
+ * setting a VP register fails. There's really no way to
+ * continue as a guest VM, so panic.
+ */
+ BUG_ON(!hv_result_success(res.a0));
+}
+EXPORT_SYMBOL_GPL(hv_set_vpreg);
+
+/*
+ * Get the value of a single VP register. One version
+ * returns just 64 bits and another returns the full 128 bits.
+ * The two versions are separate to avoid complicating the
+ * calling sequence for the more frequently used 64 bit version.
+ */
+
+void hv_get_vpreg_128(u32 msr, struct hv_get_vp_registers_output *result)
+{
+ struct arm_smccc_1_2_regs args;
+ struct arm_smccc_1_2_regs res;
+
+ args.a0 = HV_FUNC_ID;
+ args.a1 = HVCALL_GET_VP_REGISTERS | HV_HYPERCALL_FAST_BIT |
+ HV_HYPERCALL_REP_COMP_1;
+ args.a2 = HV_PARTITION_ID_SELF;
+ args.a3 = HV_VP_INDEX_SELF;
+ args.a4 = msr;
+
+ /*
+ * Use the SMCCC 1.2 interface because the results are in registers
+ * beyond X0-X3.
+ */
+ arm_smccc_1_2_hvc(&args, &res);
+
+ /*
+ * Something is fundamentally broken in the hypervisor if
+ * getting a VP register fails. There's really no way to
+ * continue as a guest VM, so panic.
+ */
+ BUG_ON(!hv_result_success(res.a0));
+
+ result->as64.low = res.a6;
+ result->as64.high = res.a7;
+}
+EXPORT_SYMBOL_GPL(hv_get_vpreg_128);
+
+u64 hv_get_vpreg(u32 msr)
+{
+ struct hv_get_vp_registers_output output;
+
+ hv_get_vpreg_128(msr, &output);
+
+ return output.as64.low;
+}
+EXPORT_SYMBOL_GPL(hv_get_vpreg);
diff --git a/arch/arm64/include/asm/hyperv-tlfs.h b/arch/arm64/include/asm/hyperv-tlfs.h
new file mode 100644
index 0000000..4d964a7
--- /dev/null
+++ b/arch/arm64/include/asm/hyperv-tlfs.h
@@ -0,0 +1,69 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * This file contains definitions from the Hyper-V Hypervisor Top-Level
+ * Functional Specification (TLFS):
+ * https://docs.microsoft.com/en-us/virtualization/hyper-v-on-windows/reference/tlfs
+ *
+ * Copyright (C) 2021, Microsoft, Inc.
+ *
+ * Author : Michael Kelley <[email protected]>
+ */
+
+#ifndef _ASM_HYPERV_TLFS_H
+#define _ASM_HYPERV_TLFS_H
+
+#include <linux/types.h>
+
+/*
+ * All data structures defined in the TLFS that are shared between Hyper-V
+ * and a guest VM use Little Endian byte ordering. This matches the default
+ * byte ordering of Linux running on ARM64, so no special handling is required.
+ */
+
+/*
+ * These Hyper-V registers provide information equivalent to the CPUID
+ * instruction on x86/x64.
+ */
+#define HV_REGISTER_HYPERVISOR_VERSION 0x00000100 /*CPUID 0x40000002 */
+#define HV_REGISTER_FEATURES 0x00000200 /*CPUID 0x40000003 */
+#define HV_REGISTER_ENLIGHTENMENTS 0x00000201 /*CPUID 0x40000004 */
+
+/*
+ * Group C Features. See the asm-generic version of hyperv-tlfs.h
+ * for a description of Feature Groups.
+ */
+
+/* Crash MSRs available */
+#define HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE BIT(8)
+
+/* STIMER direct mode is available */
+#define HV_STIMER_DIRECT_MODE_AVAILABLE BIT(13)
+
+/*
+ * Synthetic register definitions equivalent to MSRs on x86/x64
+ */
+#define HV_REGISTER_CRASH_P0 0x00000210
+#define HV_REGISTER_CRASH_P1 0x00000211
+#define HV_REGISTER_CRASH_P2 0x00000212
+#define HV_REGISTER_CRASH_P3 0x00000213
+#define HV_REGISTER_CRASH_P4 0x00000214
+#define HV_REGISTER_CRASH_CTL 0x00000215
+
+#define HV_REGISTER_GUEST_OSID 0x00090002
+#define HV_REGISTER_VP_INDEX 0x00090003
+#define HV_REGISTER_TIME_REF_COUNT 0x00090004
+#define HV_REGISTER_REFERENCE_TSC 0x00090017
+
+#define HV_REGISTER_SINT0 0x000A0000
+#define HV_REGISTER_SCONTROL 0x000A0010
+#define HV_REGISTER_SIEFP 0x000A0012
+#define HV_REGISTER_SIMP 0x000A0013
+#define HV_REGISTER_EOM 0x000A0014
+
+#define HV_REGISTER_STIMER0_CONFIG 0x000B0000
+#define HV_REGISTER_STIMER0_COUNT 0x000B0001
+
+#include <asm-generic/hyperv-tlfs.h>
+
+#endif
diff --git a/arch/arm64/include/asm/mshyperv.h b/arch/arm64/include/asm/mshyperv.h
new file mode 100644
index 0000000..20070a8
--- /dev/null
+++ b/arch/arm64/include/asm/mshyperv.h
@@ -0,0 +1,54 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * Linux-specific definitions for managing interactions with Microsoft's
+ * Hyper-V hypervisor. The definitions in this file are specific to
+ * the ARM64 architecture. See include/asm-generic/mshyperv.h for
+ * definitions are that architecture independent.
+ *
+ * Definitions that are specified in the Hyper-V Top Level Functional
+ * Spec (TLFS) should not go in this file, but should instead go in
+ * hyperv-tlfs.h.
+ *
+ * Copyright (C) 2021, Microsoft, Inc.
+ *
+ * Author : Michael Kelley <[email protected]>
+ */
+
+#ifndef _ASM_MSHYPERV_H
+#define _ASM_MSHYPERV_H
+
+#include <linux/types.h>
+#include <linux/arm-smccc.h>
+#include <asm/hyperv-tlfs.h>
+
+/*
+ * Declare calls to get and set Hyper-V VP register values on ARM64, which
+ * requires a hypercall.
+ */
+
+void hv_set_vpreg(u32 reg, u64 value);
+u64 hv_get_vpreg(u32 reg);
+void hv_get_vpreg_128(u32 reg, struct hv_get_vp_registers_output *result);
+
+static inline void hv_set_register(unsigned int reg, u64 value)
+{
+ hv_set_vpreg(reg, value);
+}
+
+static inline u64 hv_get_register(unsigned int reg)
+{
+ return hv_get_vpreg(reg);
+}
+
+/* SMCCC hypercall parameters */
+#define HV_SMCCC_FUNC_NUMBER 1
+#define HV_FUNC_ID ARM_SMCCC_CALL_VAL( \
+ ARM_SMCCC_STD_CALL, \
+ ARM_SMCCC_SMC_64, \
+ ARM_SMCCC_OWNER_VENDOR_HYP, \
+ HV_SMCCC_FUNC_NUMBER)
+
+#include <asm-generic/mshyperv.h>
+
+#endif
--
1.8.3.1
Update drivers/hv/Kconfig so CONFIG_HYPERV can be selected on
ARM64, causing the Hyper-V specific code to be built. Exclude the
Hyper-V enlightened clocks/timers code from being built for ARM64.
Signed-off-by: Michael Kelley <[email protected]>
---
drivers/hv/Kconfig | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/drivers/hv/Kconfig b/drivers/hv/Kconfig
index 66c794d..e509d5d 100644
--- a/drivers/hv/Kconfig
+++ b/drivers/hv/Kconfig
@@ -4,7 +4,8 @@ menu "Microsoft Hyper-V guest support"
config HYPERV
tristate "Microsoft Hyper-V client drivers"
- depends on X86 && ACPI && X86_LOCAL_APIC && HYPERVISOR_GUEST
+ depends on ACPI && ((X86 && X86_LOCAL_APIC && HYPERVISOR_GUEST) \
+ || (ARM64 && !CPU_BIG_ENDIAN))
select PARAVIRT
select X86_HV_CALLBACK_VECTOR
help
@@ -12,7 +13,7 @@ config HYPERV
system.
config HYPERV_TIMER
- def_bool HYPERV
+ def_bool HYPERV && X86
config HYPERV_UTILS
tristate "Microsoft Hyper-V Utilities driver"
--
1.8.3.1
On Tue, Jul 20, 2021 at 07:57:00AM -0700, Michael Kelley wrote:
> Add a function to inform Hyper-V about a guest panic.
>
> This code is built only when CONFIG_HYPERV is enabled.
>
> Signed-off-by: Michael Kelley <[email protected]>
Reviewed-by: Boqun Feng <[email protected]>
Regards,
Boqun
> ---
> arch/arm64/hyperv/hv_core.c | 52 +++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 52 insertions(+)
>
> diff --git a/arch/arm64/hyperv/hv_core.c b/arch/arm64/hyperv/hv_core.c
> index 4c5dc0f..b54c347 100644
> --- a/arch/arm64/hyperv/hv_core.c
> +++ b/arch/arm64/hyperv/hv_core.c
> @@ -127,3 +127,55 @@ u64 hv_get_vpreg(u32 msr)
> return output.as64.low;
> }
> EXPORT_SYMBOL_GPL(hv_get_vpreg);
> +
> +/*
> + * hyperv_report_panic - report a panic to Hyper-V. This function uses
> + * the older version of the Hyper-V interface that admittedly doesn't
> + * pass enough information to be useful beyond just recording the
> + * occurrence of a panic. The parallel hv_kmsg_dump() uses the
> + * new interface that allows reporting 4 Kbytes of data, which is much
> + * more useful. Hyper-V on ARM64 always supports the newer interface, but
> + * we retain support for the older version because the sysadmin is allowed
> + * to disable the newer version via sysctl in case of information security
> + * concerns about the more verbose version.
> + */
> +void hyperv_report_panic(struct pt_regs *regs, long err, bool in_die)
> +{
> + static bool panic_reported;
> + u64 guest_id;
> +
> + /* Don't report a panic to Hyper-V if we're not going to panic */
> + if (in_die && !panic_on_oops)
> + return;
> +
> + /*
> + * We prefer to report panic on 'die' chain as we have proper
> + * registers to report, but if we miss it (e.g. on BUG()) we need
> + * to report it on 'panic'.
> + *
> + * Calling code in the 'die' and 'panic' paths ensures that only
> + * one CPU is running this code, so no atomicity is needed.
> + */
> + if (panic_reported)
> + return;
> + panic_reported = true;
> +
> + guest_id = hv_get_vpreg(HV_REGISTER_GUEST_OSID);
> +
> + /*
> + * Hyper-V provides the ability to store only 5 values.
> + * Pick the passed in error value, the guest_id, the PC,
> + * and the SP.
> + */
> + hv_set_vpreg(HV_REGISTER_CRASH_P0, err);
> + hv_set_vpreg(HV_REGISTER_CRASH_P1, guest_id);
> + hv_set_vpreg(HV_REGISTER_CRASH_P2, regs->pc);
> + hv_set_vpreg(HV_REGISTER_CRASH_P3, regs->sp);
> + hv_set_vpreg(HV_REGISTER_CRASH_P4, 0);
> +
> + /*
> + * Let Hyper-V know there is crash data available
> + */
> + hv_set_vpreg(HV_REGISTER_CRASH_CTL, HV_CRASH_CTL_CRASH_NOTIFY);
> +}
> +EXPORT_SYMBOL_GPL(hyperv_report_panic);
> --
> 1.8.3.1
>
On Tue, Jul 20, 2021 at 07:57:03AM -0700, Michael Kelley wrote:
> Update drivers/hv/Kconfig so CONFIG_HYPERV can be selected on
> ARM64, causing the Hyper-V specific code to be built. Exclude the
> Hyper-V enlightened clocks/timers code from being built for ARM64.
>
> Signed-off-by: Michael Kelley <[email protected]>
FWIW,
Reviewed-by: Boqun Feng <[email protected]>
Regards,
Boqun
> ---
> drivers/hv/Kconfig | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/hv/Kconfig b/drivers/hv/Kconfig
> index 66c794d..e509d5d 100644
> --- a/drivers/hv/Kconfig
> +++ b/drivers/hv/Kconfig
> @@ -4,7 +4,8 @@ menu "Microsoft Hyper-V guest support"
>
> config HYPERV
> tristate "Microsoft Hyper-V client drivers"
> - depends on X86 && ACPI && X86_LOCAL_APIC && HYPERVISOR_GUEST
> + depends on ACPI && ((X86 && X86_LOCAL_APIC && HYPERVISOR_GUEST) \
> + || (ARM64 && !CPU_BIG_ENDIAN))
> select PARAVIRT
> select X86_HV_CALLBACK_VECTOR
> help
> @@ -12,7 +13,7 @@ config HYPERV
> system.
>
> config HYPERV_TIMER
> - def_bool HYPERV
> + def_bool HYPERV && X86
>
> config HYPERV_UTILS
> tristate "Microsoft Hyper-V Utilities driver"
> --
> 1.8.3.1
>
On Tue, Jul 20, 2021 at 07:57:01AM -0700, Michael Kelley wrote:
> Add ARM64-specific code to initialize the Hyper-V
> hypervisor when booting as a guest VM.
>
> This code is built only when CONFIG_HYPERV is enabled.
>
> Signed-off-by: Michael Kelley <[email protected]>
FWIW,
Reviewed-by: Boqun Feng <[email protected]>
Regards,
Boqun
> ---
> arch/arm64/hyperv/Makefile | 2 +-
> arch/arm64/hyperv/mshyperv.c | 83 ++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 84 insertions(+), 1 deletion(-)
> create mode 100644 arch/arm64/hyperv/mshyperv.c
>
> diff --git a/arch/arm64/hyperv/Makefile b/arch/arm64/hyperv/Makefile
> index 1697d30..87c31c0 100644
> --- a/arch/arm64/hyperv/Makefile
> +++ b/arch/arm64/hyperv/Makefile
> @@ -1,2 +1,2 @@
> # SPDX-License-Identifier: GPL-2.0
> -obj-y := hv_core.o
> +obj-y := hv_core.o mshyperv.o
> diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
> new file mode 100644
> index 0000000..2811fd0
> --- /dev/null
> +++ b/arch/arm64/hyperv/mshyperv.c
> @@ -0,0 +1,83 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +/*
> + * Core routines for interacting with Microsoft's Hyper-V hypervisor,
> + * including hypervisor initialization.
> + *
> + * Copyright (C) 2021, Microsoft, Inc.
> + *
> + * Author : Michael Kelley <[email protected]>
> + */
> +
> +#include <linux/types.h>
> +#include <linux/acpi.h>
> +#include <linux/export.h>
> +#include <linux/errno.h>
> +#include <linux/version.h>
> +#include <linux/cpuhotplug.h>
> +#include <asm/mshyperv.h>
> +
> +static bool hyperv_initialized;
> +
> +static int __init hyperv_init(void)
> +{
> + struct hv_get_vp_registers_output result;
> + u32 a, b, c, d;
> + u64 guest_id;
> + int ret;
> +
> + /*
> + * If we're in a VM on Hyper-V, the ACPI hypervisor_id field will
> + * have the string "MsHyperV".
> + */
> + if (strncmp((char *)&acpi_gbl_FADT.hypervisor_id, "MsHyperV", 8))
> + return -EINVAL;
> +
> + /* Setup the guest ID */
> + guest_id = generate_guest_id(0, LINUX_VERSION_CODE, 0);
> + hv_set_vpreg(HV_REGISTER_GUEST_OSID, guest_id);
> +
> + /* Get the features and hints from Hyper-V */
> + hv_get_vpreg_128(HV_REGISTER_FEATURES, &result);
> + ms_hyperv.features = result.as32.a;
> + ms_hyperv.priv_high = result.as32.b;
> + ms_hyperv.misc_features = result.as32.c;
> +
> + hv_get_vpreg_128(HV_REGISTER_ENLIGHTENMENTS, &result);
> + ms_hyperv.hints = result.as32.a;
> +
> + pr_info("Hyper-V: privilege flags low 0x%x, high 0x%x, hints 0x%x, misc 0x%x\n",
> + ms_hyperv.features, ms_hyperv.priv_high, ms_hyperv.hints,
> + ms_hyperv.misc_features);
> +
> + /* Get information about the Hyper-V host version */
> + hv_get_vpreg_128(HV_REGISTER_HYPERVISOR_VERSION, &result);
> + a = result.as32.a;
> + b = result.as32.b;
> + c = result.as32.c;
> + d = result.as32.d;
> + pr_info("Hyper-V: Host Build %d.%d.%d.%d-%d-%d\n",
> + b >> 16, b & 0xFFFF, a, d & 0xFFFFFF, c, d >> 24);
> +
> + ret = hv_common_init();
> + if (ret)
> + return ret;
> +
> + ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "arm64/hyperv_init:online",
> + hv_common_cpu_init, hv_common_cpu_die);
> + if (ret < 0) {
> + hv_common_free();
> + return ret;
> + }
> +
> + hyperv_initialized = true;
> + return 0;
> +}
> +
> +early_initcall(hyperv_init);
> +
> +bool hv_is_hyperv_initialized(void)
> +{
> + return hyperv_initialized;
> +}
> +EXPORT_SYMBOL_GPL(hv_is_hyperv_initialized);
> --
> 1.8.3.1
>
> Subject: [PATCH v11 3/5] arm64: hyperv: Initialize hypervisor on boot
>
> Add ARM64-specific code to initialize the Hyper-V
> hypervisor when booting as a guest VM.
>
> This code is built only when CONFIG_HYPERV is enabled.
>
> Signed-off-by: Michael Kelley <[email protected]>
> ---
> arch/arm64/hyperv/Makefile | 2 +-
> arch/arm64/hyperv/mshyperv.c | 83 ++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 84 insertions(+), 1 deletion(-)
> create mode 100644 arch/arm64/hyperv/mshyperv.c
>
> diff --git a/arch/arm64/hyperv/Makefile b/arch/arm64/hyperv/Makefile
> index 1697d30..87c31c0 100644
> --- a/arch/arm64/hyperv/Makefile
> +++ b/arch/arm64/hyperv/Makefile
> @@ -1,2 +1,2 @@
> # SPDX-License-Identifier: GPL-2.0
> -obj-y := hv_core.o
> +obj-y := hv_core.o mshyperv.o
> diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
> new file mode 100644
> index 0000000..2811fd0
> --- /dev/null
> +++ b/arch/arm64/hyperv/mshyperv.c
> @@ -0,0 +1,83 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +/*
> + * Core routines for interacting with Microsoft's Hyper-V hypervisor,
> + * including hypervisor initialization.
> + *
> + * Copyright (C) 2021, Microsoft, Inc.
> + *
> + * Author : Michael Kelley <[email protected]>
> + */
> +
> +#include <linux/types.h>
> +#include <linux/acpi.h>
> +#include <linux/export.h>
> +#include <linux/errno.h>
> +#include <linux/version.h>
> +#include <linux/cpuhotplug.h>
> +#include <asm/mshyperv.h>
> +
> +static bool hyperv_initialized;
> +
> +static int __init hyperv_init(void)
> +{
> + struct hv_get_vp_registers_output result;
> + u32 a, b, c, d;
> + u64 guest_id;
> + int ret;
> +
> + /*
> + * If we're in a VM on Hyper-V, the ACPI hypervisor_id field will
> + * have the string "MsHyperV".
> + */
> + if (strncmp((char *)&acpi_gbl_FADT.hypervisor_id, "MsHyperV", 8))
> + return -EINVAL;
> +
> + /* Setup the guest ID */
> + guest_id = generate_guest_id(0, LINUX_VERSION_CODE, 0);
> + hv_set_vpreg(HV_REGISTER_GUEST_OSID, guest_id);
> +
> + /* Get the features and hints from Hyper-V */
> + hv_get_vpreg_128(HV_REGISTER_FEATURES, &result);
> + ms_hyperv.features = result.as32.a;
> + ms_hyperv.priv_high = result.as32.b;
> + ms_hyperv.misc_features = result.as32.c;
> +
> + hv_get_vpreg_128(HV_REGISTER_ENLIGHTENMENTS, &result);
> + ms_hyperv.hints = result.as32.a;
> +
> + pr_info("Hyper-V: privilege flags low 0x%x, high 0x%x, hints 0x%x, misc 0x%x\n",
> + ms_hyperv.features, ms_hyperv.priv_high, ms_hyperv.hints,
> + ms_hyperv.misc_features);
> +
> + /* Get information about the Hyper-V host version */
> + hv_get_vpreg_128(HV_REGISTER_HYPERVISOR_VERSION, &result);
> + a = result.as32.a;
> + b = result.as32.b;
> + c = result.as32.c;
> + d = result.as32.d;
> + pr_info("Hyper-V: Host Build %d.%d.%d.%d-%d-%d\n",
> + b >> 16, b & 0xFFFF, a, d & 0xFFFFFF, c, d >> 24);
> +
> + ret = hv_common_init();
> + if (ret)
> + return ret;
> +
> + ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "arm64/hyperv_init:online",
> + hv_common_cpu_init, hv_common_cpu_die);
> + if (ret < 0) {
> + hv_common_free();
> + return ret;
> + }
> +
> + hyperv_initialized = true;
> + return 0;
> +}
> +
> +early_initcall(hyperv_init);
> +
> +bool hv_is_hyperv_initialized(void)
> +{
> + return hyperv_initialized;
> +}
> +EXPORT_SYMBOL_GPL(hv_is_hyperv_initialized);
> --
> 1.8.3.1
Reviewed-by: Sunil Muthuswamy <[email protected]>
> Add a function to inform Hyper-V about a guest panic.
>
> This code is built only when CONFIG_HYPERV is enabled.
>
> Signed-off-by: Michael Kelley <[email protected]>
> ---
> arch/arm64/hyperv/hv_core.c | 52 +++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 52 insertions(+)
>
> diff --git a/arch/arm64/hyperv/hv_core.c b/arch/arm64/hyperv/hv_core.c
> index 4c5dc0f..b54c347 100644
> --- a/arch/arm64/hyperv/hv_core.c
> +++ b/arch/arm64/hyperv/hv_core.c
> @@ -127,3 +127,55 @@ u64 hv_get_vpreg(u32 msr)
> return output.as64.low;
> }
> EXPORT_SYMBOL_GPL(hv_get_vpreg);
> +
> +/*
> + * hyperv_report_panic - report a panic to Hyper-V. This function uses
> + * the older version of the Hyper-V interface that admittedly doesn't
> + * pass enough information to be useful beyond just recording the
> + * occurrence of a panic. The parallel hv_kmsg_dump() uses the
> + * new interface that allows reporting 4 Kbytes of data, which is much
> + * more useful. Hyper-V on ARM64 always supports the newer interface, but
> + * we retain support for the older version because the sysadmin is allowed
> + * to disable the newer version via sysctl in case of information security
> + * concerns about the more verbose version.
> + */
> +void hyperv_report_panic(struct pt_regs *regs, long err, bool in_die)
> +{
> + static bool panic_reported;
> + u64 guest_id;
> +
> + /* Don't report a panic to Hyper-V if we're not going to panic */
> + if (in_die && !panic_on_oops)
> + return;
> +
> + /*
> + * We prefer to report panic on 'die' chain as we have proper
> + * registers to report, but if we miss it (e.g. on BUG()) we need
> + * to report it on 'panic'.
> + *
> + * Calling code in the 'die' and 'panic' paths ensures that only
> + * one CPU is running this code, so no atomicity is needed.
> + */
> + if (panic_reported)
> + return;
> + panic_reported = true;
> +
> + guest_id = hv_get_vpreg(HV_REGISTER_GUEST_OSID);
> +
> + /*
> + * Hyper-V provides the ability to store only 5 values.
> + * Pick the passed in error value, the guest_id, the PC,
> + * and the SP.
> + */
> + hv_set_vpreg(HV_REGISTER_CRASH_P0, err);
> + hv_set_vpreg(HV_REGISTER_CRASH_P1, guest_id);
> + hv_set_vpreg(HV_REGISTER_CRASH_P2, regs->pc);
> + hv_set_vpreg(HV_REGISTER_CRASH_P3, regs->sp);
> + hv_set_vpreg(HV_REGISTER_CRASH_P4, 0);
> +
> + /*
> + * Let Hyper-V know there is crash data available
> + */
> + hv_set_vpreg(HV_REGISTER_CRASH_CTL, HV_CRASH_CTL_CRASH_NOTIFY);
> +}
> +EXPORT_SYMBOL_GPL(hyperv_report_panic);
> --
> 1.8.3.1
Reviewed-by: Sunil Muthuswamy <[email protected]>
From: Michael Kelley <[email protected]> Sent: Tuesday, July 20, 2021 7:57 AM
>
> This series enables Linux guests running on Hyper-V on ARM64
> hardware. New ARM64-specific code in arch/arm64/hyperv initializes
> Hyper-V and its hypercall mechanism. Existing architecture
> independent drivers for Hyper-V's VMbus and synthetic devices just
> work when built for ARM64. Hyper-V code is built and included in
> the image and modules only if CONFIG_HYPERV is enabled.
Will and Catalin --
Gentle ping. :-) The clock/timer issues are now worked out in that
Hyper-V is providing full Generic Timer functionality in guest VMs.
That dropped some code out of the patch set, and making additional
code architecture neutral reduced the ARM64 specific code in this patch
set even further.
To my knowledge, all issues have been addressed, so I'm looking for
any further review from you as ARM64 maintainers, or your Ack so
this can be ready for the 5.15 merge window.
Thanks!
Michael
>
> The five patches are organized as follows:
>
> 1) Add definitions and functions for making Hyper-V hypercalls
> and getting/setting virtual processor registers provided by
> Hyper-V
>
> 2) Add the function needed by the arch independent VMbus driver
> for reporting a panic to Hyper-V.
>
> 3) Add Hyper-V initialization code and utility functions that
> report Hyper-v status.
>
> 4) Export screen_info so it may be used by the Hyper-V frame buffer
> driver built as a module. It is already exported for x86,
> powerpc, and alpha architectures.
>
> 5) Make CONFIG_HYPERV selectable on ARM64 in addition to x86/x64.
>
> Hyper-V on ARM64 runs with a 4 Kbyte page size, but allows guests
> with 4K/16K/64K page size. Linux guests with this patch series
> work with all three supported ARM64 page sizes.
>
> The Hyper-V vPCI driver at drivers/pci/host/pci-hyperv.c has
> x86/x64-specific code and is not being built for ARM64. Enabling
> Hyper-V vPCI devices on ARM64 is in progress via a separate set
> of patches.
>
> This patch set is based on the linux-next20210720 code tree.
>
> Changes in v11:
> * Drop the previous Patch 1 as the fixes have already been
> separately accepted upstream.
> * Drop the previous Patch 3 for enabling Hyper-V enlightened
> clocks/timers. Hyper-V is now offering the full ARM64
> architectural Generic Timer in guest VMs, so the existing
> arch_arch_timer.c driver just works. [Mark Rutland, Marc
> Zyngier]
> * Simplified the previous Patch 4 and Patch 5 (now Patch 2 and 3)
> by sharing more code between the x86 and ARM64 architectures.
> * Combined hyperv_early_init() and hyperv_init() into a single
> initialization function that runs as an early_initcall. This
> is possible because the Hyper-V enlightened clocks/timers
> no longer need to be initialized early in the boot sequence.
>
> Changes in v10:
> * Drop previous Patch 1 for SMCCC v1.2 HVC calls in favor of
> Sudeep Holla's patch [Mark Rutland]
> * Use new helper functions in 5.13 for checking Hyper-V hypercall
> return status
> * Set up per-CPU hypercall argument page that is now used by the
> Hyper-V balloon driver
> * Rebase on 5.13-RC1
>
> Changes in v9:
> * Added Patch 1 to enable making an SMCCC compliant hypercall
> that returns results in other than registers X0 thru X3, per
> version 1.2 and later of the SMCCC spec.
> * Using the ability to return results in registers X6 and X7,
> converted hv_get_vpreg_128() to use a "fast" hypercall that
> passes inputs and outputs in registers, and in doing so eliminated
> a lot of memory allocation complexity.
> * Cleaned up some extra blank lines and use of spaces in aligning
> local variables. [Sunil Muthuswamy]
> * Based on discussion about future directions, reverted the
> population of hv_vp_index array to use a cpuhp state instead
> of a hypercall, which is like it was in v7 and earlier.
>
> Changes in v8:
> * Removed a lot of code based on refactoring the boundary between
> arch independent and arch dependent code for Hyper-V, per comments
> from Arnd Bergmann. The removed code was either duplicated on
> the x86 side, or has been folded into architecture independent
> code as not really being architecture dependent.
> * Added config dependency on !CONFIG_CPU_BIG_ENDIAN [Arnd Bergmann]
> * Reworked the approach to Hyper-V initialization. The functionality
> is the same, but is now structured like the Xen code with an early
> init function called in setup_arch() and an early initcall to
> finish the initialization. [Arnd Bergmann]
>
> Changes in v7:
> * Separately upstreamed split of hyperv-tlfs.h into arch dependent
> and independent versions. In this patch set, update the ARM64
> hyperv-tlfs.h to include architecture independent definitions.
> This approach eliminates a lot of lines of otherwise duplicated
> code on the ARM64 side.
> * Break ARM64 mshyperv.h into smaller pieces. Have an initial
> baseline, and add code along with patches for a particular
> functional area. [Marc Zyngier]
> * In mshyperv.h, use static inline functions instead of #defines
> where possible. [Arnd Bergmann]
> * Use VMbus INTID obtained from ACPI DSDT instead of hardcoding.
> The STIMER INTID is still hardcoded because it is needed
> before Linux has initialized the ACPI subsystem, so it can't
> be obtained from the DSDT. Wedging it into the GTDT seems
> dubious, so was not done. [Marc Zyngier]
> * Update Hyper-V page size allocation functions to use
> alloc_page() if PAGE_SIZE == HV_HYP_PAGE_SIZE [Arnd
> Bergmann]
> * Various other minor changes based on feedback and to rebase
> to latest linux-next [Marc Zyngier and Arnd Bergmann]
>
> Changes in v6:
> * Use SMCCC hypercall interface instead of direct invocation
> of HVC instruction and the Hyper-V hypercall interface
> [Marc Zyngier]
> * Reimplemented functions to alloc/free Hyper-V size pages
> using kmalloc/kfree since kmalloc now guarantees alignment of
> power of 2 size allocations [Marc Zyngier]
> * Export screen_info in arm64 architecture so it can be used
> by the Hyper-V buffer driver built as a module
> * Renamed source file arch/arm64/hyperv/hv_init.c to hv_core.c
> to better reflect its content
> * Fixed the bit position of certain feature flags presented by
> Hyper-V to the guest. The bit positions on ARM64 don't match
> the position on x86 like originally thought.
> * Minor fixups to rebase to 5.6-rc5 linux-next
>
> Changes in v5:
> * Minor fixups to rebase to 5.4-rc1 linux-next
>
> Changes in v4:
> * Moved clock-related code into an architecture independent
> Hyper-V clocksource driver that is already upstream. Clock
> related code is removed from this patch set except for the
> ARM64 specific interrupt handler. [Marc Zyngier]
> * Separately upstreamed the split of mshyperv.h into arch independent
> and arch dependent portions. The arch independent portion has been
> removed from this patch set.
> * Divided patch #2 of the series into multiple smaller patches
> [Marc Zyngier]
> * Changed a dozen or so smaller things based on feedback
> [Marc Zyngier, Will Deacon]
> * Added functions to alloc/free Hyper-V size pages for use by
> drivers for Hyper-V synthetic devices when updated to not assume
> guest page size and Hyper-v page size are the same
>
> Changes in v3:
> * Added initialization of hv_vp_index array like was recently
> added on x86 branch [KY Srinivasan]
> * Changed Hyper-V ARM64 register symbols to be all uppercase
> instead of mixed case [KY Srinivasan]
> * Separated mshyperv.h into two files, one architecture
> independent and one architecture dependent. After this code
> is upstream, will make changes to the x86 code to use the
> architecture independent file and remove duplication. And
> once we have a multi-architecture Hyper-V TLFS, will do a
> separate patch to split hyperv-tlfs.h in the same way.
> [KY Srinivasan]
> * Minor tweaks to rebase to latest linux-next code
>
> Changes in v2:
> * Removed patch to implement slow_virt_to_phys() on ARM64.
> Use of slow_virt_to_phys() in arch independent Hyper-V
> drivers has been eliminated by commit 6ba34171bcbd
> ("Drivers: hv: vmbus: Remove use of slow_virt_to_phys()")
> * Minor tweaks to rebase to latest linux-next code
>
> Michael Kelley (5):
> arm64: hyperv: Add Hyper-V hypercall and register access utilities
> arm64: hyperv: Add panic handler
> arm64: hyperv: Initialize hypervisor on boot
> arm64: efi: Export screen_info
> Drivers: hv: Enable Hyper-V code to be built on ARM64
>
> MAINTAINERS | 3 +
> arch/arm64/Kbuild | 1 +
> arch/arm64/hyperv/Makefile | 2 +
> arch/arm64/hyperv/hv_core.c | 181 +++++++++++++++++++++++++++++++++++
> arch/arm64/hyperv/mshyperv.c | 83 ++++++++++++++++
> arch/arm64/include/asm/hyperv-tlfs.h | 69 +++++++++++++
> arch/arm64/include/asm/mshyperv.h | 54 +++++++++++
> arch/arm64/kernel/efi.c | 1 +
> drivers/hv/Kconfig | 5 +-
> 9 files changed, 397 insertions(+), 2 deletions(-)
> create mode 100644 arch/arm64/hyperv/Makefile
> create mode 100644 arch/arm64/hyperv/hv_core.c
> create mode 100644 arch/arm64/hyperv/mshyperv.c
> create mode 100644 arch/arm64/include/asm/hyperv-tlfs.h
> create mode 100644 arch/arm64/include/asm/mshyperv.h
>
> --
> 1.8.3.1
On Tue, 20 Jul 2021 15:57:01 +0100,
Michael Kelley <[email protected]> wrote:
>
> Add ARM64-specific code to initialize the Hyper-V
> hypervisor when booting as a guest VM.
>
> This code is built only when CONFIG_HYPERV is enabled.
>
> Signed-off-by: Michael Kelley <[email protected]>
> ---
> arch/arm64/hyperv/Makefile | 2 +-
> arch/arm64/hyperv/mshyperv.c | 83 ++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 84 insertions(+), 1 deletion(-)
> create mode 100644 arch/arm64/hyperv/mshyperv.c
>
> diff --git a/arch/arm64/hyperv/Makefile b/arch/arm64/hyperv/Makefile
> index 1697d30..87c31c0 100644
> --- a/arch/arm64/hyperv/Makefile
> +++ b/arch/arm64/hyperv/Makefile
> @@ -1,2 +1,2 @@
> # SPDX-License-Identifier: GPL-2.0
> -obj-y := hv_core.o
> +obj-y := hv_core.o mshyperv.o
> diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
> new file mode 100644
> index 0000000..2811fd0
> --- /dev/null
> +++ b/arch/arm64/hyperv/mshyperv.c
> @@ -0,0 +1,83 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +/*
> + * Core routines for interacting with Microsoft's Hyper-V hypervisor,
> + * including hypervisor initialization.
> + *
> + * Copyright (C) 2021, Microsoft, Inc.
> + *
> + * Author : Michael Kelley <[email protected]>
> + */
> +
> +#include <linux/types.h>
> +#include <linux/acpi.h>
> +#include <linux/export.h>
> +#include <linux/errno.h>
> +#include <linux/version.h>
> +#include <linux/cpuhotplug.h>
> +#include <asm/mshyperv.h>
> +
> +static bool hyperv_initialized;
> +
> +static int __init hyperv_init(void)
> +{
> + struct hv_get_vp_registers_output result;
> + u32 a, b, c, d;
> + u64 guest_id;
> + int ret;
> +
> + /*
> + * If we're in a VM on Hyper-V, the ACPI hypervisor_id field will
> + * have the string "MsHyperV".
> + */
> + if (strncmp((char *)&acpi_gbl_FADT.hypervisor_id, "MsHyperV", 8))
> + return -EINVAL;
Before going ahead and parsing the local FADT copy, it would be
prudent to test that you are actually on an ACPI system, specially
given that this function is unconditionally called, even on DT
systems. In the same vein, returning -EINVAL when failing to find
Hyper-V is a bit excessive.
> +
> + /* Setup the guest ID */
> + guest_id = generate_guest_id(0, LINUX_VERSION_CODE, 0);
> + hv_set_vpreg(HV_REGISTER_GUEST_OSID, guest_id);
> +
> + /* Get the features and hints from Hyper-V */
> + hv_get_vpreg_128(HV_REGISTER_FEATURES, &result);
> + ms_hyperv.features = result.as32.a;
> + ms_hyperv.priv_high = result.as32.b;
> + ms_hyperv.misc_features = result.as32.c;
> +
> + hv_get_vpreg_128(HV_REGISTER_ENLIGHTENMENTS, &result);
> + ms_hyperv.hints = result.as32.a;
> +
> + pr_info("Hyper-V: privilege flags low 0x%x, high 0x%x, hints 0x%x, misc 0x%x\n",
> + ms_hyperv.features, ms_hyperv.priv_high, ms_hyperv.hints,
> + ms_hyperv.misc_features);
> +
> + /* Get information about the Hyper-V host version */
> + hv_get_vpreg_128(HV_REGISTER_HYPERVISOR_VERSION, &result);
> + a = result.as32.a;
> + b = result.as32.b;
> + c = result.as32.c;
> + d = result.as32.d;
> + pr_info("Hyper-V: Host Build %d.%d.%d.%d-%d-%d\n",
> + b >> 16, b & 0xFFFF, a, d & 0xFFFFFF, c, d >> 24);
> +
> + ret = hv_common_init();
> + if (ret)
> + return ret;
> +
> + ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "arm64/hyperv_init:online",
> + hv_common_cpu_init, hv_common_cpu_die);
> + if (ret < 0) {
> + hv_common_free();
> + return ret;
> + }
> +
> + hyperv_initialized = true;
> + return 0;
> +}
> +
> +early_initcall(hyperv_init);
> +
> +bool hv_is_hyperv_initialized(void)
> +{
> + return hyperv_initialized;
> +}
> +EXPORT_SYMBOL_GPL(hv_is_hyperv_initialized);
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
On Tue, 20 Jul 2021 15:56:58 +0100,
Michael Kelley <[email protected]> wrote:
>
> This series enables Linux guests running on Hyper-V on ARM64
> hardware. New ARM64-specific code in arch/arm64/hyperv initializes
> Hyper-V and its hypercall mechanism. Existing architecture
> independent drivers for Hyper-V's VMbus and synthetic devices just
> work when built for ARM64. Hyper-V code is built and included in
> the image and modules only if CONFIG_HYPERV is enabled.
>
> The five patches are organized as follows:
>
> 1) Add definitions and functions for making Hyper-V hypercalls
> and getting/setting virtual processor registers provided by
> Hyper-V
>
> 2) Add the function needed by the arch independent VMbus driver
> for reporting a panic to Hyper-V.
>
> 3) Add Hyper-V initialization code and utility functions that
> report Hyper-v status.
>
> 4) Export screen_info so it may be used by the Hyper-V frame buffer
> driver built as a module. It is already exported for x86,
> powerpc, and alpha architectures.
>
> 5) Make CONFIG_HYPERV selectable on ARM64 in addition to x86/x64.
>
> Hyper-V on ARM64 runs with a 4 Kbyte page size, but allows guests
> with 4K/16K/64K page size. Linux guests with this patch series
> work with all three supported ARM64 page sizes.
>
> The Hyper-V vPCI driver at drivers/pci/host/pci-hyperv.c has
> x86/x64-specific code and is not being built for ARM64. Enabling
> Hyper-V vPCI devices on ARM64 is in progress via a separate set
> of patches.
>
> This patch set is based on the linux-next20210720 code tree.
>
> Changes in v11:
> * Drop the previous Patch 1 as the fixes have already been
> separately accepted upstream.
> * Drop the previous Patch 3 for enabling Hyper-V enlightened
> clocks/timers. Hyper-V is now offering the full ARM64
> architectural Generic Timer in guest VMs, so the existing
> arch_arch_timer.c driver just works. [Mark Rutland, Marc
> Zyngier]
Thanks for doing this. Assuming you fix the issue I mentioned in my
reply to patch #3. FWIW:
Acked-by: Marc Zyngier <[email protected]>
M.
--
Without deviation from the norm, progress is not possible.
On Tue, Jul 20, 2021 at 07:57:01AM -0700, Michael Kelley wrote:
> Add ARM64-specific code to initialize the Hyper-V
> hypervisor when booting as a guest VM.
>
> This code is built only when CONFIG_HYPERV is enabled.
>
> Signed-off-by: Michael Kelley <[email protected]>
> ---
> arch/arm64/hyperv/Makefile | 2 +-
> arch/arm64/hyperv/mshyperv.c | 83 ++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 84 insertions(+), 1 deletion(-)
> create mode 100644 arch/arm64/hyperv/mshyperv.c
>
> diff --git a/arch/arm64/hyperv/Makefile b/arch/arm64/hyperv/Makefile
> index 1697d30..87c31c0 100644
> --- a/arch/arm64/hyperv/Makefile
> +++ b/arch/arm64/hyperv/Makefile
> @@ -1,2 +1,2 @@
> # SPDX-License-Identifier: GPL-2.0
> -obj-y := hv_core.o
> +obj-y := hv_core.o mshyperv.o
> diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
> new file mode 100644
> index 0000000..2811fd0
> --- /dev/null
> +++ b/arch/arm64/hyperv/mshyperv.c
> @@ -0,0 +1,83 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +/*
> + * Core routines for interacting with Microsoft's Hyper-V hypervisor,
> + * including hypervisor initialization.
> + *
> + * Copyright (C) 2021, Microsoft, Inc.
> + *
> + * Author : Michael Kelley <[email protected]>
> + */
> +
> +#include <linux/types.h>
> +#include <linux/acpi.h>
> +#include <linux/export.h>
> +#include <linux/errno.h>
> +#include <linux/version.h>
> +#include <linux/cpuhotplug.h>
> +#include <asm/mshyperv.h>
> +
> +static bool hyperv_initialized;
> +
> +static int __init hyperv_init(void)
> +{
> + struct hv_get_vp_registers_output result;
> + u32 a, b, c, d;
> + u64 guest_id;
> + int ret;
As Marc suggests, before looking at the FADT, you need something like:
/*
* Hyper-V VMs always have ACPI.
*/
if (acpi_disabled)
return 0;
... where `acpi_disabled` is defined in <linux/acpi.h> (or via its
includes), so you don't need to include any additional headers.
> +
> + /*
> + * If we're in a VM on Hyper-V, the ACPI hypervisor_id field will
> + * have the string "MsHyperV".
> + */
> + if (strncmp((char *)&acpi_gbl_FADT.hypervisor_id, "MsHyperV", 8))
> + return -EINVAL;
As Marc suggests, it's no an error for a platform to not have Hyper-V,
so returning 0 in tihs case would be preferable.
Otherwise this looks fine to me.
Thanks,
Mark.
> +
> + /* Setup the guest I[D */
> + guest_id = generate_guest_id(0, LINUX_VERSION_CODE, 0);
> + hv_set_vpreg(HV_REGISTER_GUEST_OSID, guest_id);
> +
> + /* Get the features and hints from Hyper-V */
> + hv_get_vpreg_128(HV_REGISTER_FEATURES, &result);
> + ms_hyperv.features = result.as32.a;
> + ms_hyperv.priv_high = result.as32.b;
> + ms_hyperv.misc_features = result.as32.c;
> +
> + hv_get_vpreg_128(HV_REGISTER_ENLIGHTENMENTS, &result);
> + ms_hyperv.hints = result.as32.a;
> +
> + pr_info("Hyper-V: privilege flags low 0x%x, high 0x%x, hints 0x%x, misc 0x%x\n",
> + ms_hyperv.features, ms_hyperv.priv_high, ms_hyperv.hints,
> + ms_hyperv.misc_features);
> +
> + /* Get information about the Hyper-V host version */
> + hv_get_vpreg_128(HV_REGISTER_HYPERVISOR_VERSION, &result);
> + a = result.as32.a;
> + b = result.as32.b;
> + c = result.as32.c;
> + d = result.as32.d;
> + pr_info("Hyper-V: Host Build %d.%d.%d.%d-%d-%d\n",
> + b >> 16, b & 0xFFFF, a, d & 0xFFFFFF, c, d >> 24);
> +
> + ret = hv_common_init();
> + if (ret)
> + return ret;
> +
> + ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "arm64/hyperv_init:online",
> + hv_common_cpu_init, hv_common_cpu_die);
> + if (ret < 0) {
> + hv_common_free();
> + return ret;
> + }
> +
> + hyperv_initialized = true;
> + return 0;
> +}
> +
> +early_initcall(hyperv_init);
> +
> +bool hv_is_hyperv_initialized(void)
> +{
> + return hyperv_initialized;
> +}
> +EXPORT_SYMBOL_GPL(hv_is_hyperv_initialized);
> --
> 1.8.3.1
>
On Mon, Aug 02, 2021 at 05:01:02PM +0100, Marc Zyngier wrote:
> On Tue, 20 Jul 2021 15:56:58 +0100,
> Michael Kelley <[email protected]> wrote:
> >
> > This series enables Linux guests running on Hyper-V on ARM64
> > hardware. New ARM64-specific code in arch/arm64/hyperv initializes
> > Hyper-V and its hypercall mechanism. Existing architecture
> > independent drivers for Hyper-V's VMbus and synthetic devices just
> > work when built for ARM64. Hyper-V code is built and included in
> > the image and modules only if CONFIG_HYPERV is enabled.
> >
> > The five patches are organized as follows:
> >
> > 1) Add definitions and functions for making Hyper-V hypercalls
> > and getting/setting virtual processor registers provided by
> > Hyper-V
> >
> > 2) Add the function needed by the arch independent VMbus driver
> > for reporting a panic to Hyper-V.
> >
> > 3) Add Hyper-V initialization code and utility functions that
> > report Hyper-v status.
> >
> > 4) Export screen_info so it may be used by the Hyper-V frame buffer
> > driver built as a module. It is already exported for x86,
> > powerpc, and alpha architectures.
> >
> > 5) Make CONFIG_HYPERV selectable on ARM64 in addition to x86/x64.
> >
> > Hyper-V on ARM64 runs with a 4 Kbyte page size, but allows guests
> > with 4K/16K/64K page size. Linux guests with this patch series
> > work with all three supported ARM64 page sizes.
> >
> > The Hyper-V vPCI driver at drivers/pci/host/pci-hyperv.c has
> > x86/x64-specific code and is not being built for ARM64. Enabling
> > Hyper-V vPCI devices on ARM64 is in progress via a separate set
> > of patches.
> >
> > This patch set is based on the linux-next20210720 code tree.
> >
> > Changes in v11:
> > * Drop the previous Patch 1 as the fixes have already been
> > separately accepted upstream.
> > * Drop the previous Patch 3 for enabling Hyper-V enlightened
> > clocks/timers. Hyper-V is now offering the full ARM64
> > architectural Generic Timer in guest VMs, so the existing
> > arch_arch_timer.c driver just works. [Mark Rutland, Marc
> > Zyngier]
>
> Thanks for doing this. Assuming you fix the issue I mentioned in my
> reply to patch #3. FWIW:
>
> Acked-by: Marc Zyngier <[email protected]>
I've tried to provide concrete options for those. With those fixed up
somehow:
Acked-by: Mark Rutland <[email protected]>
Mark.
From: Mark Rutland <[email protected]> Sent: Monday, August 2, 2021 9:26 AM
>
> On Tue, Jul 20, 2021 at 07:57:01AM -0700, Michael Kelley wrote:
> > Add ARM64-specific code to initialize the Hyper-V
> > hypervisor when booting as a guest VM.
> >
> > This code is built only when CONFIG_HYPERV is enabled.
> >
> > Signed-off-by: Michael Kelley <[email protected]>
> > ---
> > arch/arm64/hyperv/Makefile | 2 +-
> > arch/arm64/hyperv/mshyperv.c | 83 ++++++++++++++++++++++++++++++++++++++++++++
> > 2 files changed, 84 insertions(+), 1 deletion(-)
> > create mode 100644 arch/arm64/hyperv/mshyperv.c
> >
> > diff --git a/arch/arm64/hyperv/Makefile b/arch/arm64/hyperv/Makefile
> > index 1697d30..87c31c0 100644
> > --- a/arch/arm64/hyperv/Makefile
> > +++ b/arch/arm64/hyperv/Makefile
> > @@ -1,2 +1,2 @@
> > # SPDX-License-Identifier: GPL-2.0
> > -obj-y := hv_core.o
> > +obj-y := hv_core.o mshyperv.o
> > diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
> > new file mode 100644
> > index 0000000..2811fd0
> > --- /dev/null
> > +++ b/arch/arm64/hyperv/mshyperv.c
> > @@ -0,0 +1,83 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +/*
> > + * Core routines for interacting with Microsoft's Hyper-V hypervisor,
> > + * including hypervisor initialization.
> > + *
> > + * Copyright (C) 2021, Microsoft, Inc.
> > + *
> > + * Author : Michael Kelley <[email protected]>
> > + */
> > +
> > +#include <linux/types.h>
> > +#include <linux/acpi.h>
> > +#include <linux/export.h>
> > +#include <linux/errno.h>
> > +#include <linux/version.h>
> > +#include <linux/cpuhotplug.h>
> > +#include <asm/mshyperv.h>
> > +
> > +static bool hyperv_initialized;
> > +
> > +static int __init hyperv_init(void)
> > +{
> > + struct hv_get_vp_registers_output result;
> > + u32 a, b, c, d;
> > + u64 guest_id;
> > + int ret;
>
> As Marc suggests, before looking at the FADT, you need something like:
>
> /*
> * Hyper-V VMs always have ACPI.
> */
> if (acpi_disabled)
> return 0;
>
> ... where `acpi_disabled` is defined in <linux/acpi.h> (or via its
> includes), so you don't need to include any additional headers.
>
> > +
> > + /*
> > + * If we're in a VM on Hyper-V, the ACPI hypervisor_id field will
> > + * have the string "MsHyperV".
> > + */
> > + if (strncmp((char *)&acpi_gbl_FADT.hypervisor_id, "MsHyperV", 8))
> > + return -EINVAL;
>
> As Marc suggests, it's no an error for a platform to not have Hyper-V,
> so returning 0 in tihs case would be preferable.
>
> Otherwise this looks fine to me.
>
Thanks Marc and Mark. Good point that the code should cleanly
handle the case where a kernel is built with CONFIG_HYPERV but
running somewhere other than as a Hyper-V guest.
Michael