LinuxLists.cc - [PATCH v8 0/7] KVM: x86: Allow Qemu/KVM to use PVH entry point

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Subject: [PATCH v8 1/7] xen/pvh: Split CONFIG_XEN_PVH into CONFIG_PVH and CONFIG_XEN_PVH

In order to pave the way for hypervisors other than Xen to use the PVH
entry point for VMs, we need to factor the PVH entry code into Xen specific
and hypervisor agnostic components. The first step in doing that, is to
create a new config option for PVH entry that can be enabled
independently from CONFIG_XEN.

Signed-off-by: Maran Wilson <[email protected]>
Reviewed-by: Juergen Gross <[email protected]>
---
arch/x86/Kconfig | 6 ++++++
arch/x86/kernel/head_64.S | 2 +-
arch/x86/xen/Kconfig | 3 ++-
3 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 8689e794a43c..c2a22a74abee 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -796,6 +796,12 @@ config KVM_GUEST
underlying device model, the host provides the guest with
timing infrastructure such as time of day, and system time

+config PVH
+ bool "Support for running PVH guests"
+ ---help---
+ This option enables the PVH entry point for guest virtual machines
+ as specified in the x86/HVM direct boot ABI.
+
config KVM_DEBUG_FS
bool "Enable debug information for KVM Guests in debugfs"
depends on KVM_GUEST && DEBUG_FS
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 747c758f67b7..d1dbe8e4eb82 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -386,7 +386,7 @@ NEXT_PAGE(early_dynamic_pgts)

.data

-#if defined(CONFIG_XEN_PV) || defined(CONFIG_XEN_PVH)
+#if defined(CONFIG_XEN_PV) || defined(CONFIG_PVH)
NEXT_PGD_PAGE(init_top_pgt)
.quad level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE_NOENC
.org init_top_pgt + L4_PAGE_OFFSET*8, 0
diff --git a/arch/x86/xen/Kconfig b/arch/x86/xen/Kconfig
index 1ef391aa184d..e07abefd3d26 100644
--- a/arch/x86/xen/Kconfig
+++ b/arch/x86/xen/Kconfig
@@ -74,6 +74,7 @@ config XEN_DEBUG_FS
Enabling this option may incur a significant performance overhead.

config XEN_PVH
- bool "Support for running as a PVH guest"
+ bool "Support for running as a Xen PVH guest"
depends on XEN && XEN_PVHVM && ACPI
+ select PVH
def_bool n
--
2.16.1

2018-12-06 06:07:03

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Subject: [PATCH v8 2/7] xen/pvh: Move PVH entry code out of Xen specific tree

Once hypervisors other than Xen start using the PVH entry point for
starting VMs, we would like the option of being able to compile PVH entry
capable kernels without enabling CONFIG_XEN and all the code that comes
along with that. To allow that, we are moving the PVH code out of Xen and
into files sitting at a higher level in the tree.

This patch is not introducing any code or functional changes, just moving
files from one location to another.

Signed-off-by: Maran Wilson <[email protected]>
Reviewed-by: Konrad Rzeszutek Wilk <[email protected]>
Reviewed-by: Juergen Gross <[email protected]>
---
MAINTAINERS | 1 +
arch/x86/Kbuild | 2 ++
arch/x86/platform/pvh/Makefile | 5 +++++
arch/x86/{xen/enlighten_pvh.c => platform/pvh/enlighten.c} | 0
arch/x86/{xen/xen-pvh.S => platform/pvh/head.S} | 0
arch/x86/xen/Makefile | 4 ----
6 files changed, 8 insertions(+), 4 deletions(-)
create mode 100644 arch/x86/platform/pvh/Makefile
rename arch/x86/{xen/enlighten_pvh.c => platform/pvh/enlighten.c} (100%)
rename arch/x86/{xen/xen-pvh.S => platform/pvh/head.S} (100%)

diff --git a/MAINTAINERS b/MAINTAINERS
index 6682420421c1..349115c62e4f 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -16456,6 +16456,7 @@ L: [email protected] (moderated for non-subscribers)
T: git git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip.git
S: Supported
F: arch/x86/xen/
+F: arch/x86/platform/pvh/
F: drivers/*/xen-*front.c
F: drivers/xen/
F: arch/x86/include/asm/xen/
diff --git a/arch/x86/Kbuild b/arch/x86/Kbuild
index 0038a2d10a7a..2089e4414300 100644
--- a/arch/x86/Kbuild
+++ b/arch/x86/Kbuild
@@ -7,6 +7,8 @@ obj-$(CONFIG_KVM) += kvm/
# Xen paravirtualization support
obj-$(CONFIG_XEN) += xen/

+obj-$(CONFIG_XEN_PVH) += platform/pvh/
+
# Hyper-V paravirtualization support
obj-$(subst m,y,$(CONFIG_HYPERV)) += hyperv/

diff --git a/arch/x86/platform/pvh/Makefile b/arch/x86/platform/pvh/Makefile
new file mode 100644
index 000000000000..9fd25efcd2a3
--- /dev/null
+++ b/arch/x86/platform/pvh/Makefile
@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0
+OBJECT_FILES_NON_STANDARD_head.o := y
+
+obj-$(CONFIG_XEN_PVH) += enlighten.o
+obj-$(CONFIG_XEN_PVH) += head.o
diff --git a/arch/x86/xen/enlighten_pvh.c b/arch/x86/platform/pvh/enlighten.c
similarity index 100%
rename from arch/x86/xen/enlighten_pvh.c
rename to arch/x86/platform/pvh/enlighten.c
diff --git a/arch/x86/xen/xen-pvh.S b/arch/x86/platform/pvh/head.S
similarity index 100%
rename from arch/x86/xen/xen-pvh.S
rename to arch/x86/platform/pvh/head.S
diff --git a/arch/x86/xen/Makefile b/arch/x86/xen/Makefile
index dd2550d33b38..b239922f6c6c 100644
--- a/arch/x86/xen/Makefile
+++ b/arch/x86/xen/Makefile
@@ -1,6 +1,5 @@
# SPDX-License-Identifier: GPL-2.0
OBJECT_FILES_NON_STANDARD_xen-asm_$(BITS).o := y
-OBJECT_FILES_NON_STANDARD_xen-pvh.o := y

ifdef CONFIG_FUNCTION_TRACER
# Do not profile debug and lowlevel utilities
@@ -37,9 +36,6 @@ obj-$(CONFIG_XEN_PV) += multicalls.o
obj-$(CONFIG_XEN_PV) += xen-asm.o
obj-$(CONFIG_XEN_PV) += xen-asm_$(BITS).o

-obj-$(CONFIG_XEN_PVH) += enlighten_pvh.o
-obj-$(CONFIG_XEN_PVH) += xen-pvh.o
-
obj-$(CONFIG_EVENT_TRACING) += trace.o

obj-$(CONFIG_SMP) += smp.o
--
2.16.1

2018-12-06 06:07:23

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Subject: [PATCH v8 5/7] xen/pvh: Move Xen code for getting mem map via hcall out of common file

We need to refactor PVH entry code so that support for other hypervisors
like Qemu/KVM can be added more easily.

The original design for PVH entry in Xen guests relies on being able to
obtain the memory map from the hypervisor using a hypercall. When we
extend the PVH entry ABI to support other hypervisors like Qemu/KVM,
a new mechanism will be added that allows the guest to get the memory
map without needing to use hypercalls.

For Xen guests, the hypercall approach will still be supported. In
preparation for adding support for other hypervisors, we can move the
code that uses hypercalls into the Xen specific file. This will allow us
to compile kernels in the future without CONFIG_XEN that are still capable
of being booted as a Qemu/KVM guest via the PVH entry point.

Signed-off-by: Maran Wilson <[email protected]>
Reviewed-by: Juergen Gross <[email protected]>
---
arch/x86/platform/pvh/enlighten.c | 29 ++++++++++++++---------------
arch/x86/xen/enlighten_pvh.c | 20 ++++++++++++++++++++
2 files changed, 34 insertions(+), 15 deletions(-)

diff --git a/arch/x86/platform/pvh/enlighten.c b/arch/x86/platform/pvh/enlighten.c
index 637bd74ba32d..8040b3fbf545 100644
--- a/arch/x86/platform/pvh/enlighten.c
+++ b/arch/x86/platform/pvh/enlighten.c
@@ -8,11 +8,7 @@
#include <asm/e820/api.h>
#include <asm/x86_init.h>

-#include <asm/xen/interface.h>
-#include <asm/xen/hypercall.h>
-
#include <xen/xen.h>
-#include <xen/interface/memory.h>
#include <xen/interface/hvm/start_info.h>

/*
@@ -31,21 +27,24 @@ static u64 pvh_get_root_pointer(void)
return pvh_start_info.rsdp_paddr;
}

+/*
+ * Xen guests are able to obtain the memory map from the hypervisor via the
+ * HYPERVISOR_memory_op hypercall.
+ * If we are trying to boot a Xen PVH guest, it is expected that the kernel
+ * will have been configured to provide an override for this routine to do
+ * just that.
+ */
+void __init __weak mem_map_via_hcall(struct boot_params *ptr __maybe_unused)
+{
+ xen_raw_printk("Error: Could not find memory map\n");
+ BUG();
+}
+
static void __init init_pvh_bootparams(void)
{
- struct xen_memory_map memmap;
- int rc;
-
memset(&pvh_bootparams, 0, sizeof(pvh_bootparams));

- memmap.nr_entries = ARRAY_SIZE(pvh_bootparams.e820_table);
- set_xen_guest_handle(memmap.buffer, pvh_bootparams.e820_table);
- rc = HYPERVISOR_memory_op(XENMEM_memory_map, &memmap);
- if (rc) {
- xen_raw_printk("XENMEM_memory_map failed (%d)\n", rc);
- BUG();
- }
- pvh_bootparams.e820_entries = memmap.nr_entries;
+ mem_map_via_hcall(&pvh_bootparams);

if (pvh_bootparams.e820_entries < E820_MAX_ENTRIES_ZEROPAGE - 1) {
pvh_bootparams.e820_table[pvh_bootparams.e820_entries].addr =
diff --git a/arch/x86/xen/enlighten_pvh.c b/arch/x86/xen/enlighten_pvh.c
index 41a7d6ad74e0..35b7599d2d0b 100644
--- a/arch/x86/xen/enlighten_pvh.c
+++ b/arch/x86/xen/enlighten_pvh.c
@@ -1,13 +1,18 @@
// SPDX-License-Identifier: GPL-2.0
#include <linux/acpi.h>

+#include <xen/hvc-console.h>
+
#include <asm/io_apic.h>
#include <asm/hypervisor.h>
+#include <asm/e820/api.h>

#include <xen/xen.h>
#include <asm/xen/interface.h>
#include <asm/xen/hypercall.h>

+#include <xen/interface/memory.h>
+
/*
* PVH variables.
*
@@ -28,3 +33,18 @@ void __init xen_pvh_init(void)
pfn = __pa(hypercall_page);
wrmsr_safe(msr, (u32)pfn, (u32)(pfn >> 32));
}
+
+void __init mem_map_via_hcall(struct boot_params *boot_params_p)
+{
+ struct xen_memory_map memmap;
+ int rc;
+
+ memmap.nr_entries = ARRAY_SIZE(boot_params_p->e820_table);
+ set_xen_guest_handle(memmap.buffer, boot_params_p->e820_table);
+ rc = HYPERVISOR_memory_op(XENMEM_memory_map, &memmap);
+ if (rc) {
+ xen_raw_printk("XENMEM_memory_map failed (%d)\n", rc);
+ BUG();
+ }
+ boot_params_p->e820_entries = memmap.nr_entries;
+}
--
2.16.1

2018-12-06 06:07:41

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Subject: [PATCH v8 4/7] xen/pvh: Move Xen specific PVH VM initialization out of common file

We need to refactor PVH entry code so that support for other hypervisors
like Qemu/KVM can be added more easily.

This patch moves the small block of code used for initializing Xen PVH
virtual machines into the Xen specific file. This initialization is not
going to be needed for Qemu/KVM guests. Moving it out of the common file
is going to allow us to compile kernels in the future without CONFIG_XEN
that are still capable of being booted as a Qemu/KVM guest via the PVH
entry point.

Signed-off-by: Maran Wilson <[email protected]>
Reviewed-by: Konrad Rzeszutek Wilk <[email protected]>
Reviewed-by: Juergen Gross <[email protected]>
---
arch/x86/platform/pvh/enlighten.c | 29 ++++++++++++++++++++---------
arch/x86/xen/enlighten_pvh.c | 22 +++++++++++++++++++++-
include/xen/xen.h | 3 +++
3 files changed, 44 insertions(+), 10 deletions(-)

diff --git a/arch/x86/platform/pvh/enlighten.c b/arch/x86/platform/pvh/enlighten.c
index 491932991202..637bd74ba32d 100644
--- a/arch/x86/platform/pvh/enlighten.c
+++ b/arch/x86/platform/pvh/enlighten.c
@@ -81,27 +81,38 @@ static void __init init_pvh_bootparams(void)
x86_init.acpi.get_root_pointer = pvh_get_root_pointer;
}

+/*
+ * If we are trying to boot a Xen PVH guest, it is expected that the kernel
+ * will have been configured to provide the required override for this routine.
+ */
+void __init __weak xen_pvh_init(void)
+{
+ xen_raw_printk("Error: Missing xen PVH initialization\n");
+ BUG();
+}
+
+/*
+ * When we add support for other hypervisors like Qemu/KVM, this routine can
+ * selectively invoke the appropriate initialization based on guest type.
+ */
+static void hypervisor_specific_init(void)
+{
+ xen_pvh_init();
+}
+
/*
* This routine (and those that it might call) should not use
* anything that lives in .bss since that segment will be cleared later.
*/
void __init xen_prepare_pvh(void)
{
- u32 msr;
- u64 pfn;
-
if (pvh_start_info.magic != XEN_HVM_START_MAGIC_VALUE) {
xen_raw_printk("Error: Unexpected magic value (0x%08x)\n",
pvh_start_info.magic);
BUG();
}

- xen_pvh = 1;
- xen_start_flags = pvh_start_info.flags;
-
- msr = cpuid_ebx(xen_cpuid_base() + 2);
- pfn = __pa(hypercall_page);
- wrmsr_safe(msr, (u32)pfn, (u32)(pfn >> 32));
+ hypervisor_specific_init();

init_pvh_bootparams();
}
diff --git a/arch/x86/xen/enlighten_pvh.c b/arch/x86/xen/enlighten_pvh.c
index 6be7bc719b38..41a7d6ad74e0 100644
--- a/arch/x86/xen/enlighten_pvh.c
+++ b/arch/x86/xen/enlighten_pvh.c
@@ -1,5 +1,12 @@
// SPDX-License-Identifier: GPL-2.0
-#include <linux/types.h>
+#include <linux/acpi.h>
+
+#include <asm/io_apic.h>
+#include <asm/hypervisor.h>
+
+#include <xen/xen.h>
+#include <asm/xen/interface.h>
+#include <asm/xen/hypercall.h>

/*
* PVH variables.
@@ -8,3 +15,16 @@
* after startup_{32|64} is invoked, which will clear the .bss segment.
*/
bool xen_pvh __attribute__((section(".data"))) = 0;
+
+void __init xen_pvh_init(void)
+{
+ u32 msr;
+ u64 pfn;
+
+ xen_pvh = 1;
+ xen_start_flags = pvh_start_info.flags;
+
+ msr = cpuid_ebx(xen_cpuid_base() + 2);
+ pfn = __pa(hypercall_page);
+ wrmsr_safe(msr, (u32)pfn, (u32)(pfn >> 32));
+}
diff --git a/include/xen/xen.h b/include/xen/xen.h
index d7a2678da77f..0e2156786ad2 100644
--- a/include/xen/xen.h
+++ b/include/xen/xen.h
@@ -29,6 +29,9 @@ extern bool xen_pvh;

extern uint32_t xen_start_flags;

+#include <xen/interface/hvm/start_info.h>
+extern struct hvm_start_info pvh_start_info;
+
#ifdef CONFIG_XEN_DOM0
#include <xen/interface/xen.h>
#include <asm/xen/hypervisor.h>
--
2.16.1

2018-12-06 06:07:42

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Subject: [PATCH v8 3/7] xen/pvh: Create a new file for Xen specific PVH code

We need to refactor PVH entry code so that support for other hypervisors
like Qemu/KVM can be added more easily.

The first step in that direction is to create a new file that will
eventually hold the Xen specific routines.

Signed-off-by: Maran Wilson <[email protected]>
Reviewed-by: Juergen Gross <[email protected]>
---
arch/x86/platform/pvh/enlighten.c | 5 ++---
arch/x86/xen/Makefile | 2 ++
arch/x86/xen/enlighten_pvh.c | 10 ++++++++++
3 files changed, 14 insertions(+), 3 deletions(-)
create mode 100644 arch/x86/xen/enlighten_pvh.c

diff --git a/arch/x86/platform/pvh/enlighten.c b/arch/x86/platform/pvh/enlighten.c
index 02e3ab7ff242..491932991202 100644
--- a/arch/x86/platform/pvh/enlighten.c
+++ b/arch/x86/platform/pvh/enlighten.c
@@ -18,10 +18,9 @@
/*
* PVH variables.
*
- * xen_pvh pvh_bootparams and pvh_start_info need to live in data segment
- * since they are used after startup_{32|64}, which clear .bss, are invoked.
+ * pvh_bootparams and pvh_start_info need to live in the data segment since
+ * they are used after startup_{32|64}, which clear .bss, are invoked.
*/
-bool xen_pvh __attribute__((section(".data"))) = 0;
struct boot_params pvh_bootparams __attribute__((section(".data")));
struct hvm_start_info pvh_start_info __attribute__((section(".data")));

diff --git a/arch/x86/xen/Makefile b/arch/x86/xen/Makefile
index b239922f6c6c..084de77a109e 100644
--- a/arch/x86/xen/Makefile
+++ b/arch/x86/xen/Makefile
@@ -36,6 +36,8 @@ obj-$(CONFIG_XEN_PV) += multicalls.o
obj-$(CONFIG_XEN_PV) += xen-asm.o
obj-$(CONFIG_XEN_PV) += xen-asm_$(BITS).o

+obj-$(CONFIG_XEN_PVH) += enlighten_pvh.o
+
obj-$(CONFIG_EVENT_TRACING) += trace.o

obj-$(CONFIG_SMP) += smp.o
diff --git a/arch/x86/xen/enlighten_pvh.c b/arch/x86/xen/enlighten_pvh.c
new file mode 100644
index 000000000000..6be7bc719b38
--- /dev/null
+++ b/arch/x86/xen/enlighten_pvh.c
@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/types.h>
+
+/*
+ * PVH variables.
+ *
+ * The variable xen_pvh needs to live in the data segment since it is used
+ * after startup_{32|64} is invoked, which will clear the .bss segment.
+ */
+bool xen_pvh __attribute__((section(".data"))) = 0;
--
2.16.1

2018-12-06 06:08:10

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Subject: [PATCH v8 6/7] xen/pvh: Add memory map pointer to hvm_start_info struct

The start info structure that is defined as part of the x86/HVM direct boot
ABI and used for starting Xen PVH guests would be more versatile if it also
included a way to pass information about the memory map to the guest. This
would allow KVM guests to share the same entry point.

Signed-off-by: Maran Wilson <[email protected]>
Reviewed-by: Juergen Gross <[email protected]>
---
include/xen/interface/hvm/start_info.h | 63 +++++++++++++++++++++++++++++++++-
1 file changed, 62 insertions(+), 1 deletion(-)

diff --git a/include/xen/interface/hvm/start_info.h b/include/xen/interface/hvm/start_info.h
index 648415976ead..50af9ea2ff1e 100644
--- a/include/xen/interface/hvm/start_info.h
+++ b/include/xen/interface/hvm/start_info.h
@@ -33,7 +33,7 @@
* | magic | Contains the magic value XEN_HVM_START_MAGIC_VALUE
* | | ("xEn3" with the 0x80 bit of the "E" set).
* 4 +----------------+
- * | version | Version of this structure. Current version is 0. New
+ * | version | Version of this structure. Current version is 1. New
* | | versions are guaranteed to be backwards-compatible.
* 8 +----------------+
* | flags | SIF_xxx flags.
@@ -48,6 +48,15 @@
* 32 +----------------+
* | rsdp_paddr | Physical address of the RSDP ACPI data structure.
* 40 +----------------+
+ * | memmap_paddr | Physical address of the (optional) memory map. Only
+ * | | present in version 1 and newer of the structure.
+ * 48 +----------------+
+ * | memmap_entries | Number of entries in the memory map table. Zero
+ * | | if there is no memory map being provided. Only
+ * | | present in version 1 and newer of the structure.
+ * 52 +----------------+
+ * | reserved | Version 1 and newer only.
+ * 56 +----------------+
*
* The layout of each entry in the module structure is the following:
*
@@ -62,13 +71,51 @@
* | reserved |
* 32 +----------------+
*
+ * The layout of each entry in the memory map table is as follows:
+ *
+ * 0 +----------------+
+ * | addr | Base address
+ * 8 +----------------+
+ * | size | Size of mapping in bytes
+ * 16 +----------------+
+ * | type | Type of mapping as defined between the hypervisor
+ * | | and guest. See XEN_HVM_MEMMAP_TYPE_* values below.
+ * 20 +----------------|
+ * | reserved |
+ * 24 +----------------+
+ *
* The address and sizes are always a 64bit little endian unsigned integer.
*
* NB: Xen on x86 will always try to place all the data below the 4GiB
* boundary.
+ *
+ * Version numbers of the hvm_start_info structure have evolved like this:
+ *
+ * Version 0: Initial implementation.
+ *
+ * Version 1: Added the memmap_paddr/memmap_entries fields (plus 4 bytes of
+ * padding) to the end of the hvm_start_info struct. These new
+ * fields can be used to pass a memory map to the guest. The
+ * memory map is optional and so guests that understand version 1
+ * of the structure must check that memmap_entries is non-zero
+ * before trying to read the memory map.
*/
#define XEN_HVM_START_MAGIC_VALUE 0x336ec578

+/*
+ * The values used in the type field of the memory map table entries are
+ * defined below and match the Address Range Types as defined in the "System
+ * Address Map Interfaces" section of the ACPI Specification. Please refer to
+ * section 15 in version 6.2 of the ACPI spec: http://uefi.org/specifications
+ */
+#define XEN_HVM_MEMMAP_TYPE_RAM 1
+#define XEN_HVM_MEMMAP_TYPE_RESERVED 2
+#define XEN_HVM_MEMMAP_TYPE_ACPI 3
+#define XEN_HVM_MEMMAP_TYPE_NVS 4
+#define XEN_HVM_MEMMAP_TYPE_UNUSABLE 5
+#define XEN_HVM_MEMMAP_TYPE_DISABLED 6
+#define XEN_HVM_MEMMAP_TYPE_PMEM 7
+
/*
* C representation of the x86/HVM start info layout.
*
@@ -86,6 +133,13 @@ struct hvm_start_info {
uint64_t cmdline_paddr; /* Physical address of the command line. */
uint64_t rsdp_paddr; /* Physical address of the RSDP ACPI data */
/* structure. */
+ /* All following fields only present in version 1 and newer */
+ uint64_t memmap_paddr; /* Physical address of an array of */
+ /* hvm_memmap_table_entry. */
+ uint32_t memmap_entries; /* Number of entries in the memmap table. */
+ /* Value will be zero if there is no memory */
+ /* map being provided. */
+ uint32_t reserved; /* Must be zero. */
};

struct hvm_modlist_entry {
@@ -95,4 +149,11 @@ struct hvm_modlist_entry {
uint64_t reserved;
};

+struct hvm_memmap_table_entry {
+ uint64_t addr; /* Base address of the memory region */
+ uint64_t size; /* Size of the memory region in bytes */
+ uint32_t type; /* Mapping type */
+ uint32_t reserved; /* Must be zero for Version 1. */
+};
+
#endif /* __XEN_PUBLIC_ARCH_X86_HVM_START_INFO_H__ */
--
2.16.1

2018-12-06 06:09:45

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Subject: [PATCH v8 7/7] KVM: x86: Allow Qemu/KVM to use PVH entry point

For certain applications it is desirable to rapidly boot a KVM virtual
machine. In cases where legacy hardware and software support within the
guest is not needed, Qemu should be able to boot directly into the
uncompressed Linux kernel binary without the need to run firmware.

There already exists an ABI to allow this for Xen PVH guests and the ABI
is supported by Linux and FreeBSD:

https://xenbits.xen.org/docs/unstable/misc/pvh.html

This patch enables Qemu to use that same entry point for booting KVM
guests.

Signed-off-by: Maran Wilson <[email protected]>
Suggested-by: Konrad Rzeszutek Wilk <[email protected]>
Suggested-by: Boris Ostrovsky <[email protected]>
Tested-by: Boris Ostrovsky <[email protected]>
Reviewed-by: Juergen Gross <[email protected]>
---
arch/x86/Kbuild | 2 +-
arch/x86/Kconfig | 8 ++++++++
arch/x86/platform/pvh/Makefile | 4 ++--
arch/x86/platform/pvh/enlighten.c | 42 +++++++++++++++++++++++++++++----------
4 files changed, 42 insertions(+), 14 deletions(-)

diff --git a/arch/x86/Kbuild b/arch/x86/Kbuild
index 2089e4414300..c625f57472f7 100644
--- a/arch/x86/Kbuild
+++ b/arch/x86/Kbuild
@@ -7,7 +7,7 @@ obj-$(CONFIG_KVM) += kvm/
# Xen paravirtualization support
obj-$(CONFIG_XEN) += xen/

-obj-$(CONFIG_XEN_PVH) += platform/pvh/
+obj-$(CONFIG_PVH) += platform/pvh/

# Hyper-V paravirtualization support
obj-$(subst m,y,$(CONFIG_HYPERV)) += hyperv/
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index c2a22a74abee..61d5ee30027e 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -802,6 +802,14 @@ config PVH
This option enables the PVH entry point for guest virtual machines
as specified in the x86/HVM direct boot ABI.

+config KVM_GUEST_PVH
+ bool "Support for running as a KVM PVH guest"
+ depends on KVM_GUEST
+ select PVH
+ ---help---
+ This option enables starting KVM guests via the PVH entry point as
+ specified in the x86/HVM direct boot ABI.
+
config KVM_DEBUG_FS
bool "Enable debug information for KVM Guests in debugfs"
depends on KVM_GUEST && DEBUG_FS
diff --git a/arch/x86/platform/pvh/Makefile b/arch/x86/platform/pvh/Makefile
index 9fd25efcd2a3..5dec5067c9fb 100644
--- a/arch/x86/platform/pvh/Makefile
+++ b/arch/x86/platform/pvh/Makefile
@@ -1,5 +1,5 @@
# SPDX-License-Identifier: GPL-2.0
OBJECT_FILES_NON_STANDARD_head.o := y

-obj-$(CONFIG_XEN_PVH) += enlighten.o
-obj-$(CONFIG_XEN_PVH) += head.o
+obj-$(CONFIG_PVH) += enlighten.o
+obj-$(CONFIG_PVH) += head.o
diff --git a/arch/x86/platform/pvh/enlighten.c b/arch/x86/platform/pvh/enlighten.c
index 8040b3fbf545..62f5c7045944 100644
--- a/arch/x86/platform/pvh/enlighten.c
+++ b/arch/x86/platform/pvh/enlighten.c
@@ -8,6 +8,8 @@
#include <asm/e820/api.h>
#include <asm/x86_init.h>

+#include <asm/xen/interface.h>
+
#include <xen/xen.h>
#include <xen/interface/hvm/start_info.h>

@@ -40,11 +42,28 @@ void __init __weak mem_map_via_hcall(struct boot_params *ptr __maybe_unused)
BUG();
}

-static void __init init_pvh_bootparams(void)
+static void __init init_pvh_bootparams(bool xen_guest)
{
memset(&pvh_bootparams, 0, sizeof(pvh_bootparams));

- mem_map_via_hcall(&pvh_bootparams);
+ if ((pvh_start_info.version > 0) && (pvh_start_info.memmap_entries)) {
+ struct hvm_memmap_table_entry *ep;
+ int i;
+
+ ep = __va(pvh_start_info.memmap_paddr);
+ pvh_bootparams.e820_entries = pvh_start_info.memmap_entries;
+
+ for (i = 0; i < pvh_bootparams.e820_entries ; i++, ep++) {
+ pvh_bootparams.e820_table[i].addr = ep->addr;
+ pvh_bootparams.e820_table[i].size = ep->size;
+ pvh_bootparams.e820_table[i].type = ep->type;
+ }
+ } else if (xen_guest) {
+ mem_map_via_hcall(&pvh_bootparams);
+ } else {
+ /* Non-xen guests are not supported by version 0 */
+ BUG();
+ }

if (pvh_bootparams.e820_entries < E820_MAX_ENTRIES_ZEROPAGE - 1) {
pvh_bootparams.e820_table[pvh_bootparams.e820_entries].addr =
@@ -75,7 +94,7 @@ static void __init init_pvh_bootparams(void)
* environment (i.e. hardware_subarch 0).
*/
pvh_bootparams.hdr.version = (2 << 8) | 12;
- pvh_bootparams.hdr.type_of_loader = (9 << 4) | 0; /* Xen loader */
+ pvh_bootparams.hdr.type_of_loader = ((xen_guest ? 0x9 : 0xb) << 4) | 0;

x86_init.acpi.get_root_pointer = pvh_get_root_pointer;
}
@@ -90,13 +109,10 @@ void __init __weak xen_pvh_init(void)
BUG();
}

-/*
- * When we add support for other hypervisors like Qemu/KVM, this routine can
- * selectively invoke the appropriate initialization based on guest type.
- */
-static void hypervisor_specific_init(void)
+static void hypervisor_specific_init(bool xen_guest)
{
- xen_pvh_init();
+ if (xen_guest)
+ xen_pvh_init();
}

/*
@@ -105,13 +121,17 @@ static void hypervisor_specific_init(void)
*/
void __init xen_prepare_pvh(void)
{
+
+ u32 msr = xen_cpuid_base();
+ bool xen_guest = !!msr;
+
if (pvh_start_info.magic != XEN_HVM_START_MAGIC_VALUE) {
xen_raw_printk("Error: Unexpected magic value (0x%08x)\n",
pvh_start_info.magic);
BUG();
}

- hypervisor_specific_init();
+ hypervisor_specific_init(xen_guest);

- init_pvh_bootparams();
+ init_pvh_bootparams(xen_guest);
}
--
2.16.1

2018-12-06 21:22:51

[permalink] [raw]

Subject: Re: [PATCH v8 0/7] KVM: x86: Allow Qemu/KVM to use PVH entry point

On 06/12/18 07:02, Maran Wilson wrote:
> For certain applications it is desirable to rapidly boot a KVM virtual
> machine. In cases where legacy hardware and software support within the
> guest is not needed, Qemu should be able to boot directly into the
> uncompressed Linux kernel binary without the need to run firmware.
>
> There already exists an ABI to allow this for Xen PVH guests and the ABI
> is supported by Linux and FreeBSD:
>
> https://xenbits.xen.org/docs/unstable/misc/pvh.html
>
> This patch series would enable Qemu to use that same entry point for
> booting KVM guests.

Thanks! I should be able to post a Tested-by next Monday. Boris, are
you going to pick it up for 4.21?

Paolo

2018-12-06 21:38:51

by Borislav Petkov

[permalink] [raw]

Subject: Re: [PATCH v8 0/7] KVM: x86: Allow Qemu/KVM to use PVH entry point

On Thu, Dec 06, 2018 at 10:21:12PM +0100, Paolo Bonzini wrote:
> Thanks! I should be able to post a Tested-by next Monday. Boris, are
> you going to pick it up for 4.21?

Boris me or Boris O.?

:-)

--
Regards/Gruss,
Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

2018-12-06 22:01:16

[permalink] [raw]

Subject: Re: [PATCH v8 0/7] KVM: x86: Allow Qemu/KVM to use PVH entry point

On 12/6/18 4:37 PM, Borislav Petkov wrote:
> On Thu, Dec 06, 2018 at 10:21:12PM +0100, Paolo Bonzini wrote:
>> Thanks! I should be able to post a Tested-by next Monday. Boris, are
>> you going to pick it up for 4.21?
> Boris me or Boris O.?
>
> :-)
>

O. ;-)

There are some minor changes in non-xen x86 code so it would be good to
get x86 maintainers' ack.

And as far as qemu/qboot changes, should we assume that the general
approach is acceptable? I understand that the patches will probably need
to go through some iterations but I want to make sure we have a path
forward there.

-boris

2018-12-06 22:06:39

[permalink] [raw]

Subject: Re: [PATCH v8 7/7] KVM: x86: Allow Qemu/KVM to use PVH entry point

On 06/12/18 07:06, Maran Wilson wrote:
> +config KVM_GUEST_PVH
> + bool "Support for running as a KVM PVH guest"
> + depends on KVM_GUEST
> + select PVH
> + ---help---
> + This option enables starting KVM guests via the PVH entry point as
> + specified in the x86/HVM direct boot ABI.
> +

This symbol is unused, so it can be removed.

Paolo

2018-12-06 22:13:54

[permalink] [raw]

Subject: Re: [PATCH v8 1/7] xen/pvh: Split CONFIG_XEN_PVH into CONFIG_PVH and CONFIG_XEN_PVH

On 06/12/18 07:04, Maran Wilson wrote:
> +config PVH
> + bool "Support for running PVH guests"
> + ---help---
> + This option enables the PVH entry point for guest virtual machines
> + as specified in the x86/HVM direct boot ABI.
> +

IIUC this breaks "normal" bzImage boot, so we should have something like

The resulting kernel will not boot with most x86 boot loaders
such as GRUB or SYSLINUX. Unless you plan to start the kernel
using QEMU or Xen, you probably want to say N here.

and also

depends on !EFI

because even though in principle it would be possible to write a PVH
loader for UEFI, PVH's start info does not support the EFI handover
protocol.

Paolo

2018-12-06 22:16:53

[permalink] [raw]

Subject: Re: [PATCH v8 0/7] KVM: x86: Allow Qemu/KVM to use PVH entry point

On 06/12/18 22:58, Boris Ostrovsky wrote:
> On 12/6/18 4:37 PM, Borislav Petkov wrote:
>> On Thu, Dec 06, 2018 at 10:21:12PM +0100, Paolo Bonzini wrote:
>>> Thanks! I should be able to post a Tested-by next Monday. Boris, are
>>> you going to pick it up for 4.21?
>> Boris me or Boris O.?
>>
>> :-)
>>
>
> O. ;-)
>
> There are some minor changes in non-xen x86 code so it would be good to
> get x86 maintainers' ack.

It's not really code, only Kconfig (and I remarked on it just now), but
it doesn't hurt of course.

> And as far as qemu/qboot changes, should we assume that the general
> approach is acceptable? I understand that the patches will probably need
> to go through some iterations but I want to make sure we have a path
> forward there.

Yes, the general approach is fine. I have already reviewed the qboot
parts, I guess we will also want an option ROM similar to
linuxboot/multiboot for SeaBIOS support but that's simple matter of
programming. :)

Paolo

2018-12-06 22:38:37

[permalink] [raw]

Subject: Re: [PATCH v8 1/7] xen/pvh: Split CONFIG_XEN_PVH into CONFIG_PVH and CONFIG_XEN_PVH

On 12/6/18 5:11 PM, Paolo Bonzini wrote:
> On 06/12/18 07:04, Maran Wilson wrote:
>> +config PVH
>> + bool "Support for running PVH guests"
>> + ---help---
>> + This option enables the PVH entry point for guest virtual machines
>> + as specified in the x86/HVM direct boot ABI.
>> +
> IIUC this breaks "normal" bzImage boot, so we should have something like
>
> The resulting kernel will not boot with most x86 boot loaders
> such as GRUB

Grub support for PVH guests (for Xen) is well under way.

> or SYSLINUX. Unless you plan to start the kernel
> using QEMU or Xen, you probably want to say N here.

I think PVH should not be user-selectable at all. It should be selected
by either XEN_PVH or KVM_GUEST_PVH (which you suggested to drop).

>
> and also
>
> depends on !EFI
>
> because even though in principle it would be possible to write a PVH
> loader for UEFI, PVH's start info does not support the EFI handover
> protocol.

But we should be able to build the binary with both EFI and PVH?

-boris

2018-12-06 22:50:21

[permalink] [raw]

Subject: Re: [PATCH v8 1/7] xen/pvh: Split CONFIG_XEN_PVH into CONFIG_PVH and CONFIG_XEN_PVH

On 06/12/18 23:34, Boris Ostrovsky wrote:
> On 12/6/18 5:11 PM, Paolo Bonzini wrote:
>> On 06/12/18 07:04, Maran Wilson wrote:
>>> +config PVH
>>> + bool "Support for running PVH guests"
>>> + ---help---
>>> + This option enables the PVH entry point for guest virtual machines
>>> + as specified in the x86/HVM direct boot ABI.
>>> +
>> IIUC this breaks "normal" bzImage boot, so we should have something like
>>
>> The resulting kernel will not boot with most x86 boot loaders
>> such as GRUB
>
>
> Grub support for PVH guests (for Xen) is well under way.

Oh, nice. :)

>> or SYSLINUX. Unless you plan to start the kernel
>> using QEMU or Xen, you probably want to say N here.
>
> I think PVH should not be user-selectable at all. It should be selected
> by either XEN_PVH or KVM_GUEST_PVH (which you suggested to drop).

KVM_GUEST_PVH is not entirely accurate because it's not just for KVM (it
can be used with QEMU and Apple's Hypervisor.framework for example).

It's also not necessarily just for QEMU (it could be implemented for
kvmtool if desired), but as long as it's in the help I guess it's
acceptable.

I think we could just drop the sentence about boot loaders from my
suggestion.

>>
>> and also
>>
>> depends on !EFI
>>
>> because even though in principle it would be possible to write a PVH
>> loader for UEFI, PVH's start info does not support the EFI handover
>> protocol.
>
> But we should be able to build the binary with both EFI and PVH?

Can you? It's a completely different binary format, the EFI handover
protocol is invoked via a special entry point and needs the Linux header
format, not ELF.

Paolo

2018-12-06 23:13:26

[permalink] [raw]

Subject: Re: [PATCH v8 1/7] xen/pvh: Split CONFIG_XEN_PVH into CONFIG_PVH and CONFIG_XEN_PVH

On 12/6/18 5:49 PM, Paolo Bonzini wrote:
> On 06/12/18 23:34, Boris Ostrovsky wrote:
>> On 12/6/18 5:11 PM, Paolo Bonzini wrote:
>>
>>> and also
>>>
>>> depends on !EFI
>>>
>>> because even though in principle it would be possible to write a PVH
>>> loader for UEFI, PVH's start info does not support the EFI handover
>>> protocol.
>> But we should be able to build the binary with both EFI and PVH?
> Can you? It's a completely different binary format, the EFI handover
> protocol is invoked via a special entry point and needs the Linux header
> format, not ELF.

Right, but I think it is desirable to be able to build both from the
same config file.

-boris

2018-12-06 23:32:32

[permalink] [raw]

Subject: Re: [PATCH v8 1/7] xen/pvh: Split CONFIG_XEN_PVH into CONFIG_PVH and CONFIG_XEN_PVH

On 07/12/18 00:11, Boris Ostrovsky wrote:
> On 12/6/18 5:49 PM, Paolo Bonzini wrote:
>> On 06/12/18 23:34, Boris Ostrovsky wrote:
>>> On 12/6/18 5:11 PM, Paolo Bonzini wrote:
>>>
>>>> and also
>>>>
>>>> depends on !EFI
>>>>
>>>> because even though in principle it would be possible to write a PVH
>>>> loader for UEFI, PVH's start info does not support the EFI handover
>>>> protocol.
>>> But we should be able to build the binary with both EFI and PVH?
>> Can you? It's a completely different binary format, the EFI handover
>> protocol is invoked via a special entry point and needs the Linux header
>> format, not ELF.
>
> Right, but I think it is desirable to be able to build both from the
> same config file.

Ah, "make bzImage" and use the vmlinux for PVH, because PVH fetches the
entry point from the special note. That's clever. :)

I don't see why it should not work, and if so the "depends on !EFI" is
indeed unnecessary.

Paolo

2018-12-06 23:37:52

by Andrew Cooper

[permalink] [raw]

Subject: Re: [Xen-devel] [PATCH v8 1/7] xen/pvh: Split CONFIG_XEN_PVH into CONFIG_PVH and CONFIG_XEN_PVH

On 06/12/2018 23:30, Paolo Bonzini wrote:
> On 07/12/18 00:11, Boris Ostrovsky wrote:
>> On 12/6/18 5:49 PM, Paolo Bonzini wrote:
>>> On 06/12/18 23:34, Boris Ostrovsky wrote:
>>>> On 12/6/18 5:11 PM, Paolo Bonzini wrote:
>>>>
>>>>> and also
>>>>>
>>>>> depends on !EFI
>>>>>
>>>>> because even though in principle it would be possible to write a PVH
>>>>> loader for UEFI, PVH's start info does not support the EFI handover
>>>>> protocol.
>>>> But we should be able to build the binary with both EFI and PVH?
>>> Can you? It's a completely different binary format, the EFI handover
>>> protocol is invoked via a special entry point and needs the Linux header
>>> format, not ELF.
>> Right, but I think it is desirable to be able to build both from the
>> same config file.
> Ah, "make bzImage" and use the vmlinux for PVH, because PVH fetches the
> entry point from the special note. That's clever. :)
>
> I don't see why it should not work, and if so the "depends on !EFI" is
> indeed unnecessary.

We do strive for single binaries in the Xen world, because that is how
people actually want to consume Xen.

It is for this reason why a single xen.gz binary can be loaded as a
straight ELF (including this PVH boot protocol), or via Multiboot 1 or
2, and even do full EFI if your bootloader is up to date on its
Multiboot2 spec :)

~Andrew

2018-12-07 06:03:21

by Jürgen Groß

[permalink] [raw]

Subject: Re: [PATCH v8 1/7] xen/pvh: Split CONFIG_XEN_PVH into CONFIG_PVH and CONFIG_XEN_PVH

On 06/12/2018 23:11, Paolo Bonzini wrote:
> On 06/12/18 07:04, Maran Wilson wrote:
>> +config PVH
>> + bool "Support for running PVH guests"
>> + ---help---
>> + This option enables the PVH entry point for guest virtual machines
>> + as specified in the x86/HVM direct boot ABI.
>> +
>
> IIUC this breaks "normal" bzImage boot, so we should have something like
>
> The resulting kernel will not boot with most x86 boot loaders
> such as GRUB or SYSLINUX. Unless you plan to start the kernel
> using QEMU or Xen, you probably want to say N here.

The resulting kernel should be able to be booted either in PVH mode
via the PVH entry point or the "normal" way via the still existing
old entry point(s).

It is an _additional_ way to boot the kernel, not an exclusive
alternative.

Juergen

2018-12-07 10:26:50

by Borislav Petkov

[permalink] [raw]

Subject: Re: [PATCH v8 0/7] KVM: x86: Allow Qemu/KVM to use PVH entry point

On Thu, Dec 06, 2018 at 11:14:34PM +0100, Paolo Bonzini wrote:
> > There are some minor changes in non-xen x86 code so it would be good to
> > get x86 maintainers' ack.
>
> It's not really code, only Kconfig (and I remarked on it just now), but
> it doesn't hurt of course.

Yeah, I don't see anything objectionable.

Thx.

--
Regards/Gruss,
Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

2018-12-07 13:43:53

[permalink] [raw]

Subject: Re: [PATCH v8 1/7] xen/pvh: Split CONFIG_XEN_PVH into CONFIG_PVH and CONFIG_XEN_PVH

On 07/12/18 07:02, Juergen Gross wrote:
> On 06/12/2018 23:11, Paolo Bonzini wrote:
>> On 06/12/18 07:04, Maran Wilson wrote:
>>> +config PVH
>>> + bool "Support for running PVH guests"
>>> + ---help---
>>> + This option enables the PVH entry point for guest virtual machines
>>> + as specified in the x86/HVM direct boot ABI.
>>> +
>>
>> IIUC this breaks "normal" bzImage boot, so we should have something like
>>
>> The resulting kernel will not boot with most x86 boot loaders
>> such as GRUB or SYSLINUX. Unless you plan to start the kernel
>> using QEMU or Xen, you probably want to say N here.
>
> The resulting kernel should be able to be booted either in PVH mode
> via the PVH entry point or the "normal" way via the still existing
> old entry point(s).
>
> It is an _additional_ way to boot the kernel, not an exclusive
> alternative.

Yup, understood now. Different binaries but one build.

Paolo

2018-12-07 13:52:09

by Jürgen Groß

[permalink] [raw]

Subject: Re: [PATCH v8 1/7] xen/pvh: Split CONFIG_XEN_PVH into CONFIG_PVH and CONFIG_XEN_PVH

On 07/12/2018 14:41, Paolo Bonzini wrote:
> On 07/12/18 07:02, Juergen Gross wrote:
>> On 06/12/2018 23:11, Paolo Bonzini wrote:
>>> On 06/12/18 07:04, Maran Wilson wrote:
>>>> +config PVH
>>>> + bool "Support for running PVH guests"
>>>> + ---help---
>>>> + This option enables the PVH entry point for guest virtual machines
>>>> + as specified in the x86/HVM direct boot ABI.
>>>> +
>>>
>>> IIUC this breaks "normal" bzImage boot, so we should have something like
>>>
>>> The resulting kernel will not boot with most x86 boot loaders
>>> such as GRUB or SYSLINUX. Unless you plan to start the kernel
>>> using QEMU or Xen, you probably want to say N here.
>>
>> The resulting kernel should be able to be booted either in PVH mode
>> via the PVH entry point or the "normal" way via the still existing
>> old entry point(s).
>>
>> It is an _additional_ way to boot the kernel, not an exclusive
>> alternative.
>
> Yup, understood now. Different binaries but one build.

The PVH boot entry is in the same bzImage binary as the normal one.
Its just another entry, similar to the Xen PV boot entry. So the binary
arch/x86/boot/bzimage can be booted either on bare metal via grub2 or
other boot-loaders, as Xen PV-guest, as Xen PVH-guest, or as KVM
PVH-guest. So one build and one binary. The non-standard boot entries
(PV- or PVH-node) are found via ELF-notes by the boot loader (qemu in
case of KVM).

Juergen

2018-12-07 13:53:55

[permalink] [raw]

Subject: Re: [PATCH v8 1/7] xen/pvh: Split CONFIG_XEN_PVH into CONFIG_PVH and CONFIG_XEN_PVH

On 07/12/18 14:50, Juergen Gross wrote:
> The PVH boot entry is in the same bzImage binary as the normal one.
> Its just another entry, similar to the Xen PV boot entry. So the binary
> arch/x86/boot/bzimage can be booted either on bare metal via grub2 or
> other boot-loaders, as Xen PV-guest, as Xen PVH-guest, or as KVM
> PVH-guest. So one build and one binary. The non-standard boot entries
> (PV- or PVH-node) are found via ELF-notes by the boot loader (qemu in
> case of KVM).
>

But the bzImage is not an ELF binary, and it is compressed, isn't it?
/me is confused. :)

Paolo

2018-12-07 14:00:23

by Jürgen Groß

[permalink] [raw]

Subject: Re: [PATCH v8 1/7] xen/pvh: Split CONFIG_XEN_PVH into CONFIG_PVH and CONFIG_XEN_PVH

On 07/12/2018 14:52, Paolo Bonzini wrote:
> On 07/12/18 14:50, Juergen Gross wrote:
>> The PVH boot entry is in the same bzImage binary as the normal one.
>> Its just another entry, similar to the Xen PV boot entry. So the binary
>> arch/x86/boot/bzimage can be booted either on bare metal via grub2 or
>> other boot-loaders, as Xen PV-guest, as Xen PVH-guest, or as KVM
>> PVH-guest. So one build and one binary. The non-standard boot entries
>> (PV- or PVH-node) are found via ELF-notes by the boot loader (qemu in
>> case of KVM).
>>
>
> But the bzImage is not an ELF binary, and it is compressed, isn't it?
> /me is confused. :)

grub2 (and qemu, too) can decompress it. And the decompressed result
"vmlinux" is an ELF-binary.

Juergen

2018-12-07 15:15:38

[permalink] [raw]

Subject: Re: [PATCH v8 1/7] xen/pvh: Split CONFIG_XEN_PVH into CONFIG_PVH and CONFIG_XEN_PVH

On 07/12/18 14:58, Juergen Gross wrote:
> On 07/12/2018 14:52, Paolo Bonzini wrote:
>> On 07/12/18 14:50, Juergen Gross wrote:
>>> The PVH boot entry is in the same bzImage binary as the normal one.
>>> Its just another entry, similar to the Xen PV boot entry. So the binary
>>> arch/x86/boot/bzimage can be booted either on bare metal via grub2 or
>>> other boot-loaders, as Xen PV-guest, as Xen PVH-guest, or as KVM
>>> PVH-guest. So one build and one binary. The non-standard boot entries
>>> (PV- or PVH-node) are found via ELF-notes by the boot loader (qemu in
>>> case of KVM).
>>
>> But the bzImage is not an ELF binary, and it is compressed, isn't it?
>> /me is confused. :)
>
> grub2 (and qemu, too) can decompress it. And the decompressed result
> "vmlinux" is an ELF-binary.

Aha - for KVM, the main advantage of PVH would be to skip the cost of
decompression, and that is what confused me (also we probably prefer not
having any decompression code running in QEMU, since that increases the
attack surface; there's no real disadvantage to using the existing
linuxboot code if we're given a bzImage). So, at least for now, KVM
would go with the two-binaries/one-config approach.

Sorry for having you lecture me, it's much clearer now. Thanks,

Paolo

2018-12-07 16:10:47

[permalink] [raw]

Subject: Re: [Xen-devel] [PATCH v8 0/7] KVM: x86: Allow Qemu/KVM to use PVH entry point

On 12/7/18 5:25 AM, Borislav Petkov wrote:
> On Thu, Dec 06, 2018 at 11:14:34PM +0100, Paolo Bonzini wrote:
>>> There are some minor changes in non-xen x86 code so it would be good to
>>> get x86 maintainers' ack.
>> It's not really code, only Kconfig (and I remarked on it just now), but
>> it doesn't hurt of course.
> Yeah, I don't see anything objectionable.

Can this be considered as an ACK from you?

-boris

2018-12-07 18:25:36

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Subject: Re: [PATCH v8 1/7] xen/pvh: Split CONFIG_XEN_PVH into CONFIG_PVH and CONFIG_XEN_PVH

On 12/7/2018 7:14 AM, Paolo Bonzini wrote:
> On 07/12/18 14:58, Juergen Gross wrote:
>> On 07/12/2018 14:52, Paolo Bonzini wrote:
>>> On 07/12/18 14:50, Juergen Gross wrote:
>>>> The PVH boot entry is in the same bzImage binary as the normal one.
>>>> Its just another entry, similar to the Xen PV boot entry. So the binary
>>>> arch/x86/boot/bzimage can be booted either on bare metal via grub2 or
>>>> other boot-loaders, as Xen PV-guest, as Xen PVH-guest, or as KVM
>>>> PVH-guest. So one build and one binary. The non-standard boot entries
>>>> (PV- or PVH-node) are found via ELF-notes by the boot loader (qemu in
>>>> case of KVM).
>>> But the bzImage is not an ELF binary, and it is compressed, isn't it?
>>> /me is confused. :)
>> grub2 (and qemu, too) can decompress it. And the decompressed result
>> "vmlinux" is an ELF-binary.
> Aha - for KVM, the main advantage of PVH would be to skip the cost of
> decompression, and that is what confused me (also we probably prefer not
> having any decompression code running in QEMU, since that increases the
> attack surface; there's no real disadvantage to using the existing
> linuxboot code if we're given a bzImage). So, at least for now, KVM
> would go with the two-binaries/one-config approach.

Yeah, the way we have been testing with the Qemu/qboot changes that Liam
has out for review, if you provide the bzImage binary in the -kernel
argument, legacy behavior is followed. However if you provide the
vmlinux binary (from the same kernel build), Qemu recognizes it as an
ELF binary, looks for the presence of the PVH ELFNOTE, and (if the
ELFNOTE in question is found) uses that entry point instead.

So at this point, the only feedback/comment still outstanding from you
is the one about removing KVM_GUEST_PVH right?

I'll hold off on sending a v9 until next week to see if there is any
additional feedback or test results.

Thanks,
-Maran

> Sorry for having you lecture me, it's much clearer now. Thanks,
>
> Paolo

2018-12-07 19:23:39

by Borislav Petkov

[permalink] [raw]

Subject: Re: [Xen-devel] [PATCH v8 0/7] KVM: x86: Allow Qemu/KVM to use PVH entry point

On Fri, Dec 07, 2018 at 11:07:54AM -0500, Boris Ostrovsky wrote:
> Can this be considered as an ACK from you?

I'll look at v9 next week and add tags, assuming v9 is going to be the
final one, of course.

--
Regards/Gruss,
Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)

2018-12-12 18:12:09

[permalink] [raw]

Subject: Re: [PATCH v8 0/7] KVM: x86: Allow Qemu/KVM to use PVH entry point

On 12/6/2018 1:21 PM, Paolo Bonzini wrote:
> On 06/12/18 07:02, Maran Wilson wrote:
>> For certain applications it is desirable to rapidly boot a KVM virtual
>> machine. In cases where legacy hardware and software support within the
>> guest is not needed, Qemu should be able to boot directly into the
>> uncompressed Linux kernel binary without the need to run firmware.
>>
>> There already exists an ABI to allow this for Xen PVH guests and the ABI
>> is supported by Linux and FreeBSD:
>>
>> https://xenbits.xen.org/docs/unstable/misc/pvh.html
>>
>> This patch series would enable Qemu to use that same entry point for
>> booting KVM guests.
> Thanks! I should be able to post a Tested-by next Monday. Boris, are
> you going to pick it up for 4.21?

Hi Paolo,

Are you still planning on running some testing of your own for these
patches? Should Boris wait to hear from you before moving forward?

Thanks,
-Maran

> Paolo

2018-12-12 18:20:06

[permalink] [raw]

Subject: Re: [PATCH v8 0/7] KVM: x86: Allow Qemu/KVM to use PVH entry point

On 12/12/18 1:09 PM, Maran Wilson wrote:
> On 12/6/2018 1:21 PM, Paolo Bonzini wrote:
>> On 06/12/18 07:02, Maran Wilson wrote:
>>> For certain applications it is desirable to rapidly boot a KVM virtual
>>> machine. In cases where legacy hardware and software support within the
>>> guest is not needed, Qemu should be able to boot directly into the
>>> uncompressed Linux kernel binary without the need to run firmware.
>>>
>>> There already exists an ABI to allow this for Xen PVH guests and the
>>> ABI
>>> is supported by Linux and FreeBSD:
>>>
>>> https://xenbits.xen.org/docs/unstable/misc/pvh.html
>>>
>>> This patch series would enable Qemu to use that same entry point for
>>> booting KVM guests.
>> Thanks! I should be able to post a Tested-by next Monday. Boris, are
>> you going to pick it up for 4.21?

Just realized I never answered this --- yes, I am. Now that BorisP.
acked this, having your T-b would be good.

-boris

>
> Hi Paolo,
>
> Are you still planning on running some testing of your own for these
> patches? Should Boris wait to hear from you before moving forward?
>
> Thanks,
> -Maran
>
>> Paolo
>

2018-12-13 13:16:09