Re: [PATCH v2] KVM: selftests: x86: Prioritize getting max_gfn from GuestPhysBits

[Chao Gao <chao.gao@intel.com>]

On Fri, May 10, 2024 at 10:03:46AM +0800, Tao Su wrote:
>Use the max mappable GPA via GuestPhysBits advertised by KVM to calculate
>max_gfn. Currently some selftests (e.g. access_tracking_perf_test,
>dirty_log_test...) add RAM regions close to max_gfn, so guest may access
>GPA beyond its mappable range and cause infinite loop.
>
>Adjust max_gfn in vm_compute_max_gfn() since x86 selftests already
>overrides vm_compute_max_gfn() specifically to deal with goofy edge cases.
>
>Signed-off-by: Tao Su <tao1.su@linux.intel.com>
>Tested-by: Yi Lai <yi1.lai@intel.com>
>---
>This patch is based on https://github.com/kvm-x86/linux/commit/b628cb523c65
>
>Changelog:
>v1 -> v2:
> - Only adjust vm->max_gfn in vm_compute_max_gfn()
> - Add Yi Lai's Tested-by
>
>v1: https://lore.kernel.org/all/20240508064205.15301-1-tao1.su@linux.intel.com/
>---
> tools/testing/selftests/kvm/include/x86_64/processor.h |  1 +
> tools/testing/selftests/kvm/lib/x86_64/processor.c     | 10 ++++++++--
> 2 files changed, 9 insertions(+), 2 deletions(-)
>
>diff --git a/tools/testing/selftests/kvm/include/x86_64/processor.h b/tools/testing/selftests/kvm/include/x86_64/processor.h
>index 81ce37ec407d..ff99f66d81a0 100644
>--- a/tools/testing/selftests/kvm/include/x86_64/processor.h
>+++ b/tools/testing/selftests/kvm/include/x86_64/processor.h
>@@ -282,6 +282,7 @@ struct kvm_x86_cpu_property {
> #define X86_PROPERTY_MAX_EXT_LEAF		KVM_X86_CPU_PROPERTY(0x80000000, 0, EAX, 0, 31)
> #define X86_PROPERTY_MAX_PHY_ADDR		KVM_X86_CPU_PROPERTY(0x80000008, 0, EAX, 0, 7)
> #define X86_PROPERTY_MAX_VIRT_ADDR		KVM_X86_CPU_PROPERTY(0x80000008, 0, EAX, 8, 15)
>+#define X86_PROPERTY_MAX_GUEST_PHY_ADDR		KVM_X86_CPU_PROPERTY(0x80000008, 0, EAX, 16, 23)
> #define X86_PROPERTY_SEV_C_BIT			KVM_X86_CPU_PROPERTY(0x8000001F, 0, EBX, 0, 5)
> #define X86_PROPERTY_PHYS_ADDR_REDUCTION	KVM_X86_CPU_PROPERTY(0x8000001F, 0, EBX, 6, 11)
> 
>diff --git a/tools/testing/selftests/kvm/lib/x86_64/processor.c b/tools/testing/selftests/kvm/lib/x86_64/processor.c
>index 74a4c736c9ae..aa9966ead543 100644
>--- a/tools/testing/selftests/kvm/lib/x86_64/processor.c
>+++ b/tools/testing/selftests/kvm/lib/x86_64/processor.c
>@@ -1293,10 +1293,16 @@ const struct kvm_cpuid2 *vcpu_get_supported_hv_cpuid(struct kvm_vcpu *vcpu)
> unsigned long vm_compute_max_gfn(struct kvm_vm *vm)
> {
> 	const unsigned long num_ht_pages = 12 << (30 - vm->page_shift); /* 12 GiB */
>-	unsigned long ht_gfn, max_gfn, max_pfn;
>+	unsigned long ht_gfn, max_gfn, max_pfn, max_bits = 0;

nit: max_bits has only 8 bits. so max_bits should be uint8_t.

> 	uint8_t maxphyaddr;
> 
>-	max_gfn = (1ULL << (vm->pa_bits - vm->page_shift)) - 1;
>+	if (kvm_cpu_has_p(X86_PROPERTY_MAX_GUEST_PHY_ADDR))
>+		max_bits = kvm_cpu_property(X86_PROPERTY_MAX_GUEST_PHY_ADDR);
>+
>+	if (!max_bits)
>+		max_bits = vm->pa_bits;
>+
>+	max_gfn = (1ULL << (max_bits - vm->page_shift)) - 1;
> 
> 	/* Avoid reserved HyperTransport region on AMD processors.  */
> 	if (!host_cpu_is_amd)
>
>base-commit: 448b3fe5a0eab5b625a7e15c67c7972169e47ff8
>-- 
>2.34.1
>