Now that KVM only searches for KVM's PV CPUID base when userspace sets
guest CPUID, drop the cache and simply do the search every time.
Practically speaking, this is a nop except for situations where userspace
sets CPUID _after_ running the vCPU, which is anything but a hot path,
e.g. QEMU does so only when hotplugging a vCPU. And on the flip side,
caching guest CPUID information, especially information that is used to
query/modify _other_ CPUID state, is inherently dangerous as it's all too
easy to use stale information, i.e. KVM should only cache CPUID state when
the performance and/or programming benefits justify it.
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 1 -
arch/x86/kvm/cpuid.c | 34 ++++++++-------------------------
2 files changed, 8 insertions(+), 27 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index e159e44a6a1b..f076df9f18be 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -854,7 +854,6 @@ struct kvm_vcpu_arch {
int cpuid_nent;
struct kvm_cpuid_entry2 *cpuid_entries;
- struct kvm_hypervisor_cpuid kvm_cpuid;
bool is_amd_compatible;
/*
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 3ba0e6a67823..b402b9f59cbb 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -168,12 +168,7 @@ static int kvm_cpuid_check_equal(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2
/*
* Apply runtime CPUID updates to the incoming CPUID entries to avoid
- * false positives due mismatches on KVM-owned feature flags. Note,
- * runtime CPUID updates may consume other CPUID-driven vCPU state,
- * e.g. KVM or Xen CPUID bases. Updating runtime state before full
- * CPUID processing is functionally correct only because any change in
- * CPUID is disallowed, i.e. using stale data is ok because the below
- * checks will reject the change.
+ * false positives due mismatches on KVM-owned feature flags.
*
* Note! @e2 and @nent track the _old_ CPUID entries!
*/
@@ -231,28 +226,16 @@ static struct kvm_hypervisor_cpuid kvm_get_hypervisor_cpuid(struct kvm_vcpu *vcp
vcpu->arch.cpuid_nent, sig);
}
-static struct kvm_cpuid_entry2 *__kvm_find_kvm_cpuid_features(struct kvm_cpuid_entry2 *entries,
- int nent, u32 kvm_cpuid_base)
-{
- return cpuid_entry2_find(entries, nent, kvm_cpuid_base | KVM_CPUID_FEATURES,
- KVM_CPUID_INDEX_NOT_SIGNIFICANT);
-}
-
-static struct kvm_cpuid_entry2 *kvm_find_kvm_cpuid_features(struct kvm_vcpu *vcpu)
-{
- u32 base = vcpu->arch.kvm_cpuid.base;
-
- if (!base)
- return NULL;
-
- return __kvm_find_kvm_cpuid_features(vcpu->arch.cpuid_entries,
- vcpu->arch.cpuid_nent, base);
-}
-
static u32 kvm_apply_cpuid_pv_features_quirk(struct kvm_vcpu *vcpu)
{
- struct kvm_cpuid_entry2 *best = kvm_find_kvm_cpuid_features(vcpu);
+ struct kvm_hypervisor_cpuid kvm_cpuid;
+ struct kvm_cpuid_entry2 *best;
+ kvm_cpuid = kvm_get_hypervisor_cpuid(vcpu, KVM_SIGNATURE);
+ if (!kvm_cpuid.base)
+ return 0;
+
+ best = kvm_find_cpuid_entry(vcpu, kvm_cpuid.base | KVM_CPUID_FEATURES);
if (!best)
return 0;
@@ -483,7 +466,6 @@ static int kvm_set_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2,
if (r)
goto err;
- vcpu->arch.kvm_cpuid = kvm_get_hypervisor_cpuid(vcpu, KVM_SIGNATURE);
#ifdef CONFIG_KVM_XEN
vcpu->arch.xen.cpuid = kvm_get_hypervisor_cpuid(vcpu, XEN_SIGNATURE);
#endif
--
2.47.0.338.g60cca15819-goog
