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

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

On Mon, May 13, 2024 at 10:00:35AM +0800, Tao Su wrote:
>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?

@maxphyaddr (right below) is in the same situation.

And if it was a problem for the compiler, casting vm->page_shift to uint8_t
explicitly would be a better solution.

>
>> 
>> > 	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
>> >