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.

Reviewed-by: Yuan Yao <yuan.yao@intel.com>
Link: https://lore.kernel.org/r/20230815203653.519297-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 4ba43ae..67e9f79 100644 (file)
--- 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 40ce8e6..b29c15d 100644 (file)
--- 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 31d9cbe..a0c2acb 100644 (file)
--- 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;