[PATCH AUTOSEL 6.6 01/40] x86/hyperv: Fix the detection of E820_TYPE_PRAM in a Gen2 VM

Sasha Levin
2023-11-28T21:06:24Z

From: Saurabh Sengar <ssengar@linux.microsoft.com>

[ Upstream commit 7e8037b099c0bbe8f2109dc452dbcab8d400fc53 ]

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>
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Message-ID: <1699691867-9827-1-git-send-email-ssengar@linux.microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 21556ad87f4ba..8f3a4d16bb791 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -15,6 +15,7 @@
#include <linux/io.h>
#include <asm/apic.h>
#include <asm/desc.h>
+#include <asm/e820/api.h>
#include <asm/sev.h>
#include <asm/ibt.h>
#include <asm/hypervisor.h>
@@ -286,15 +287,31 @@ 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;
--
2.42.0