kvm: x86: ensure pv_cpuid.features is initialized when enabling cap

Make the paravirtual cpuid enforcement mechanism idempotent to ioctl()
ordering by updating pv_cpuid.features whenever userspace requests the
capability. Extract this update out of kvm_update_cpuid_runtime() into a
new helper function and move its other call site into
kvm_vcpu_after_set_cpuid() where it more likely belongs.

Fixes: 66570e966dd9 ("kvm: x86: only provide PV features if enabled in guest's CPUID")
Signed-off-by: Oliver Upton <oupton@google.com>
Reviewed-by: Peter Shier <pshier@google.com>
Message-Id: <20201027231044.655110-5-oupton@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 06a278b..d50041f 100644 (file)
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -90,6 +90,20 @@ static int kvm_check_cpuid(struct kvm_cpuid_entry2 *entries, int nent)
        return 0;
 }
 
+void kvm_update_pv_runtime(struct kvm_vcpu *vcpu)
+{
+       struct kvm_cpuid_entry2 *best;
+
+       best = kvm_find_cpuid_entry(vcpu, KVM_CPUID_FEATURES, 0);
+
+       /*
+        * save the feature bitmap to avoid cpuid lookup for every PV
+        * operation
+        */
+       if (best)
+               vcpu->arch.pv_cpuid.features = best->eax;
+}
+
 void kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu)
 {
        struct kvm_cpuid_entry2 *best;
@@ -124,13 +138,6 @@ void kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu)
                (best->eax & (1 << KVM_FEATURE_PV_UNHALT)))
                best->eax &= ~(1 << KVM_FEATURE_PV_UNHALT);
 
-       /*
-        * save the feature bitmap to avoid cpuid lookup for every PV
-        * operation
-        */
-       if (best)
-               vcpu->arch.pv_cpuid.features = best->eax;
-
        if (!kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_MISC_ENABLE_NO_MWAIT)) {
                best = kvm_find_cpuid_entry(vcpu, 0x1, 0);
                if (best)
@@ -162,6 +169,8 @@ static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
                vcpu->arch.guest_supported_xcr0 =
                        (best->eax | ((u64)best->edx << 32)) & supported_xcr0;
 
+       kvm_update_pv_runtime(vcpu);
+
        vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu);
        kvm_mmu_reset_context(vcpu);
 

diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
index bf85779..f7a6e8f 100644 (file)
--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -11,6 +11,7 @@ extern u32 kvm_cpu_caps[NCAPINTS] __read_mostly;
 void kvm_set_cpu_caps(void);
 
 void kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu);
+void kvm_update_pv_runtime(struct kvm_vcpu *vcpu);
 struct kvm_cpuid_entry2 *kvm_find_cpuid_entry(struct kvm_vcpu *vcpu,
                                              u32 function, u32 index);
 int kvm_dev_ioctl_get_cpuid(struct kvm_cpuid2 *cpuid,

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index d12820a..9485611 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4611,6 +4611,8 @@ static int kvm_vcpu_ioctl_enable_cap(struct kvm_vcpu *vcpu,
 
        case KVM_CAP_ENFORCE_PV_FEATURE_CPUID:
                vcpu->arch.pv_cpuid.enforce = cap->args[0];
+               if (vcpu->arch.pv_cpuid.enforce)
+                       kvm_update_pv_runtime(vcpu);
 
                return 0;