linux-kernel - [PATCH v2 08/21] KVM: x86/mmu: Use KVM-governed feature framework to track "GBPAGES enabled"

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Message-ID: <20230729011608.1065019-9-seanjc@google.com>
Date:   Fri, 28 Jul 2023 18:15:55 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH v2 08/21] KVM: x86/mmu: Use KVM-governed feature framework to
 track "GBPAGES enabled"

Use the governed feature framework to track whether or not the guest can
use 1GiB pages, and drop the one-off helper that wraps the surprisingly
non-trivial logic surrounding 1GiB page usage in the guest.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/cpuid.c             | 17 +++++++++++++++++
 arch/x86/kvm/governed_features.h |  2 ++
 arch/x86/kvm/mmu/mmu.c           | 20 +++-----------------
 3 files changed, 22 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index ef826568c222..f74d6c404551 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -312,11 +312,28 @@ static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 {
 	struct kvm_lapic *apic = vcpu->arch.apic;
 	struct kvm_cpuid_entry2 *best;
+	bool allow_gbpages;
 
 	BUILD_BUG_ON(KVM_NR_GOVERNED_FEATURES > KVM_MAX_NR_GOVERNED_FEATURES);
 	bitmap_zero(vcpu->arch.governed_features.enabled,
 		    KVM_MAX_NR_GOVERNED_FEATURES);
 
+	/*
+	 * 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.
+	 * If TDP is disabled, honor *only* guest CPUID as KVM has full control
+	 * and can install smaller shadow pages if the host lacks 1GiB support.
+	 */
+	allow_gbpages = tdp_enabled ? boot_cpu_has(X86_FEATURE_GBPAGES) :
+				      guest_cpuid_has(vcpu, X86_FEATURE_GBPAGES);
+	if (allow_gbpages)
+		kvm_governed_feature_set(vcpu, X86_FEATURE_GBPAGES);
+
 	best = kvm_find_cpuid_entry(vcpu, 1);
 	if (best && apic) {
 		if (cpuid_entry_has(best, X86_FEATURE_TSC_DEADLINE_TIMER))
diff --git a/arch/x86/kvm/governed_features.h b/arch/x86/kvm/governed_features.h
index 40ce8e6608cd..b29c15d5e038 100644
--- a/arch/x86/kvm/governed_features.h
+++ b/arch/x86/kvm/governed_features.h
@@ -5,5 +5,7 @@ BUILD_BUG()
 
 #define KVM_GOVERNED_X86_FEATURE(x) KVM_GOVERNED_FEATURE(X86_FEATURE_##x)
 
+KVM_GOVERNED_X86_FEATURE(GBPAGES)
+
 #undef KVM_GOVERNED_X86_FEATURE
 #undef KVM_GOVERNED_FEATURE
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index ec169f5c7dce..7b9104b054bc 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4808,28 +4808,13 @@ static void __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_guest_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->cpu_role.base.level, is_efer_nx(context),
-				guest_can_use_gbpages(vcpu),
+				guest_can_use(vcpu, X86_FEATURE_GBPAGES),
 				is_cr4_pse(context),
 				guest_cpuid_is_amd_or_hygon(vcpu));
 }
@@ -4906,7 +4891,8 @@ static void reset_shadow_zero_bits_mask(struct kvm_vcpu *vcpu,
 	__reset_rsvds_bits_mask(shadow_zero_check, reserved_hpa_bits(),
 				context->root_role.level,
 				context->root_role.efer_nx,
-				guest_can_use_gbpages(vcpu), is_pse, is_amd);
+				guest_can_use(vcpu, X86_FEATURE_GBPAGES),
+				is_pse, is_amd);
 
 	if (!shadow_me_mask)
 		return;
-- 
2.41.0.487.g6d72f3e995-goog