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

[Tao Su <tao1.su@linux.intel.com>]

On Mon, May 13, 2024 at 09:44:32AM +0800, Chao Gao wrote:
> 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.

Because vm->pa_bits is unsigned int, I'm worried that the compiler will
complain on stricter compilation, what do you think?

> 
> > 	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
> >