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, 7 insertions(+), 28 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index aabf1648a56a..3003e99155e7 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -858,7 +858,6 @@ 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 93a7399dc0db..7290f91c422c 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -269,28 +269,16 @@ 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;
@@ -491,13 +479,6 @@ static int kvm_set_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2,
* whether the supplied CPUID data is equal to what's already set.
*/
if (kvm_vcpu_has_run(vcpu)) {
- /*
- * 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 KVM will reject the change.
- */
kvm_update_cpuid_runtime(vcpu);
kvm_apply_cpuid_pv_features_quirk(vcpu);
@@ -519,7 +500,6 @@ 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
--
2.45.0.215.g3402c0e53f-goog
