KVM: x86/mmu: Use KVM-governed feature framework to track "GBPAGES enabled"

[linux-2.6-microblaze.git] / arch / x86 / kvm / cpuid.c

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))