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From:   Dexuan Cui <decui@microsoft.com>
To:     kys@microsoft.com, haiyangz@microsoft.com, wei.liu@kernel.org,
        tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
        dave.hansen@linux.intel.com, linux-hyperv@vger.kernel.org,
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Cc:     x86@kernel.org, linux-kernel@vger.kernel.org,
        Dexuan Cui <decui@microsoft.com>,
        Saurabh Sengar <ssengar@linux.microsoft.com>
Subject: [PATCH] x86/hyperv: Fix the detection of E820_TYPE_PRAM in a Gen2 VM
Date:   Thu, 10 Aug 2023 22:31:37 -0700
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A Gen2 VM doesn't support legacy PCI/PCIe, so both raw_pci_ops and
raw_pci_ext_ops are NULL, and pci_subsys_init() -> pcibios_init()
doesn't call pcibios_resource_survey() -> e820__reserve_resources_late();
as a result, any emulated persistent memory of E820_TYPE_PRAM (12) via
the kernel parameter memmap=nn[KMG]!ss is not added into iomem_resource
and hence can't be detected by register_e820_pmem().

Fix this by directly calling e820__reserve_resources_late() in
hv_pci_init(), which is called from arch_initcall(pci_arch_init).

It's ok to move a Gen2 VM's e820__reserve_resources_late() from
subsys_initcall(pci_subsys_init) to arch_initcall(pci_arch_init) because
the code in-between doesn't depend on the E820 resources.
e820__reserve_resources_late() depends on e820__reserve_resources(),
which has been called earlier from setup_arch().

For a Gen-2 VM, the new hv_pci_init() also adds any memory of
E820_TYPE_PMEM (7) into iomem_resource, and acpi_nfit_register_region() ->
acpi_nfit_insert_resource() -> region_intersects() returns
REGION_INTERSECTS, so the memory of E820_TYPE_PMEM won't get added twice.

Changed the local variable "int gen2vm" to "bool gen2vm".

Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
Signed-off-by: Dexuan Cui <decui@microsoft.com>
---
 arch/x86/hyperv/hv_init.c | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index b004370d3b01..6b22d49aee7b 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -13,6 +13,7 @@
 #include <linux/io.h>
 #include <asm/apic.h>
 #include <asm/desc.h>
+#include <asm/e820/api.h>
 #include <asm/sev.h>
 #include <asm/hypervisor.h>
 #include <asm/hyperv-tlfs.h>
@@ -282,15 +283,31 @@ static int hv_cpu_die(unsigned int cpu)
 
 static int __init hv_pci_init(void)
 {
-	int gen2vm = efi_enabled(EFI_BOOT);
+	bool gen2vm = efi_enabled(EFI_BOOT);
 
 	/*
-	 * For Generation-2 VM, we exit from pci_arch_init() by returning 0.
-	 * The purpose is to suppress the harmless warning:
+	 * A Generation-2 VM doesn't support legacy PCI/PCIe, so both
+	 * raw_pci_ops and raw_pci_ext_ops are NULL, and pci_subsys_init() ->
+	 * pcibios_init() doesn't call pcibios_resource_survey() ->
+	 * e820__reserve_resources_late(); as a result, any emulated persistent
+	 * memory of E820_TYPE_PRAM (12) via the kernel parameter
+	 * memmap=nn[KMG]!ss is not added into iomem_resource and hence can't be
+	 * detected by register_e820_pmem(). Fix this by directly calling
+	 * e820__reserve_resources_late() here: e820__reserve_resources_late()
+	 * depends on e820__reserve_resources(), which has been called earlier
+	 * from setup_arch(). Note: e820__reserve_resources_late() also adds
+	 * any memory of E820_TYPE_PMEM (7) into iomem_resource, and
+	 * acpi_nfit_register_region() -> acpi_nfit_insert_resource() ->
+	 * region_intersects() returns REGION_INTERSECTS, so the memory of
+	 * E820_TYPE_PMEM won't get added twice.
+	 *
+	 * We return 0 here so that pci_arch_init() won't print the warning:
 	 * "PCI: Fatal: No config space access function found"
 	 */
-	if (gen2vm)
+	if (gen2vm) {
+		e820__reserve_resources_late();
 		return 0;
+	}
 
 	/* For Generation-1 VM, we'll proceed in pci_arch_init().  */
 	return 1;
-- 
2.25.1