From 27de925044e18eb056d6157305c841b1408621b5 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Tue, 22 Jun 2021 10:57:39 -0700 Subject: [PATCH] KVM: x86/mmu: Let guest use GBPAGES if supported in hardware and TDP is on Let the guest use 1g hugepages if TDP is enabled and the host supports GBPAGES, KVM can't actively prevent the guest from using 1g pages in this case since they can't be disabled in the hardware page walker. While injecting a page fault if a bogus 1g page is encountered during a software page walk is perfectly reasonable since KVM is simply honoring userspace's vCPU model, doing so arguably doesn't provide any meaningful value, and at worst will be horribly confusing as the guest will see inconsistent behavior and seemingly spurious page faults. Signed-off-by: Sean Christopherson Message-Id: <20210622175739.3610207-55-seanjc@google.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/mmu/mmu.c | 20 +++++++++++++++++--- 1 file changed, 17 insertions(+), 3 deletions(-) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 690f560..0073275 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -4174,13 +4174,28 @@ __reset_rsvds_bits_mask(struct rsvd_bits_validate *rsvd_check, } } +static bool guest_can_use_gbpages(struct kvm_vcpu *vcpu) +{ + /* + * If TDP is enabled, let the guest use GBPAGES if they're supported in + * hardware. The hardware page walker doesn't let KVM disable GBPAGES, + * i.e. won't treat them as reserved, and KVM doesn't redo the GVA->GPA + * walk for performance and complexity reasons. Not to mention KVM + * _can't_ solve the problem because GVA->GPA walks aren't visible to + * KVM once a TDP translation is installed. Mimic hardware behavior so + * that KVM's is at least consistent, i.e. doesn't randomly inject #PF. + */ + return tdp_enabled ? boot_cpu_has(X86_FEATURE_GBPAGES) : + guest_cpuid_has(vcpu, X86_FEATURE_GBPAGES); +} + static void reset_rsvds_bits_mask(struct kvm_vcpu *vcpu, struct kvm_mmu *context) { __reset_rsvds_bits_mask(&context->guest_rsvd_check, vcpu->arch.reserved_gpa_bits, context->root_level, is_efer_nx(context), - guest_cpuid_has(vcpu, X86_FEATURE_GBPAGES), + guest_can_use_gbpages(vcpu), is_cr4_pse(context), guest_cpuid_is_amd_or_hygon(vcpu)); } @@ -4259,8 +4274,7 @@ static void reset_shadow_zero_bits_mask(struct kvm_vcpu *vcpu, shadow_zero_check = &context->shadow_zero_check; __reset_rsvds_bits_mask(shadow_zero_check, reserved_hpa_bits(), context->shadow_root_level, uses_nx, - guest_cpuid_has(vcpu, X86_FEATURE_GBPAGES), - is_pse, is_amd); + guest_can_use_gbpages(vcpu), is_pse, is_amd); if (!shadow_me_mask) return; -- 2.7.4