On 11/11/2023 7:55 AM, Sean Christopherson wrote:
When updating guest CPUID entries to emulate runtime behavior, e.g. when
the guest enables a CR4-based feature that is tied to a CPUID flag, also
update the vCPU's cpu_caps accordingly. This will allow replacing all
usage of guest_cpuid_has() with guest_cpu_cap_has().
Take care not to update guest capabilities when KVM is updating CPUID
entries that *may* become the vCPU's CPUID, e.g. if userspace tries to set
bogus CPUID information. No extra call to update cpu_caps is needed as
the cpu_caps are initialized from the incoming guest CPUID, i.e. will
automatically get the updated values.
Note, none of the features in question use guest_cpu_cap_has() at this
time, i.e. aside from settings bits in cpu_caps, this is a glorified nop.
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/kvm/cpuid.c | 48 +++++++++++++++++++++++++++++++-------------
1 file changed, 34 insertions(+), 14 deletions(-)
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 36bd04030989..37a991439fe6 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -262,31 +262,48 @@ static u64 cpuid_get_supported_xcr0(struct kvm_cpuid_entry2 *entries, int nent)
return (best->eax | ((u64)best->edx << 32)) & kvm_caps.supported_xcr0;
}
+static __always_inline void kvm_update_feature_runtime(struct kvm_vcpu *vcpu,
+ struct kvm_cpuid_entry2 *entry,
+ unsigned int x86_feature,
+ bool has_feature)
+{
+ if (entry)
+ cpuid_entry_change(entry, x86_feature, has_feature);
+
+ if (vcpu)
+ guest_cpu_cap_change(vcpu, x86_feature, has_feature);
+}
+
static void __kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *entries,
int nent)
{
struct kvm_cpuid_entry2 *best;
+ struct kvm_vcpu *caps = vcpu;
+
+ /*
+ * Don't update vCPU capabilities if KVM is updating CPUID entries that
+ * are coming in from userspace!
+ */
+ if (entries != vcpu->arch.cpuid_entries)
+ caps = NULL;
Nit, why here we use caps instead of vcpu? Looks a bit weird.
best = cpuid_entry2_find(entries, nent, 1, KVM_CPUID_INDEX_NOT_SIGNIFICANT);
- if (best) {
- /* Update OSXSAVE bit */
- if (boot_cpu_has(X86_FEATURE_XSAVE))
- cpuid_entry_change(best, X86_FEATURE_OSXSAVE,
+
+ if (boot_cpu_has(X86_FEATURE_XSAVE))
+ kvm_update_feature_runtime(caps, best, X86_FEATURE_OSXSAVE,
kvm_is_cr4_bit_set(vcpu, X86_CR4_OSXSAVE));
- cpuid_entry_change(best, X86_FEATURE_APIC,
- vcpu->arch.apic_base & MSR_IA32_APICBASE_ENABLE);
+ kvm_update_feature_runtime(caps, best, X86_FEATURE_APIC,
+ vcpu->arch.apic_base & MSR_IA32_APICBASE_ENABLE);
- if (!kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_MISC_ENABLE_NO_MWAIT))
- cpuid_entry_change(best, X86_FEATURE_MWAIT,
- vcpu->arch.ia32_misc_enable_msr &
- MSR_IA32_MISC_ENABLE_MWAIT);
- }
+ if (!kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_MISC_ENABLE_NO_MWAIT))
+ kvm_update_feature_runtime(caps, best, X86_FEATURE_MWAIT,
+ vcpu->arch.ia32_misc_enable_msr & MSR_IA32_MISC_ENABLE_MWAIT);
> 80 characters?
best = cpuid_entry2_find(entries, nent, 7, 0);
- if (best && boot_cpu_has(X86_FEATURE_PKU))
- cpuid_entry_change(best, X86_FEATURE_OSPKE,
- kvm_is_cr4_bit_set(vcpu, X86_CR4_PKE));
+ if (boot_cpu_has(X86_FEATURE_PKU))
+ kvm_update_feature_runtime(caps, best, X86_FEATURE_OSPKE,
+ kvm_is_cr4_bit_set(vcpu, X86_CR4_PKE));
best = cpuid_entry2_find(entries, nent, 0xD, 0);
if (best)
@@ -353,6 +370,9 @@ static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
* Reset guest capabilities to userspace's guest CPUID definition, i.e.
* honor userspace's definition for features that don't require KVM or
* hardware management/support (or that KVM simply doesn't care about).
+ *
+ * Note, KVM has already done runtime updates on guest CPUID, i.e. this
+ * will also correctly set runtime features in guest CPU capabilities.
*/
for (i = 0; i < NR_KVM_CPU_CAPS; i++) {
const struct cpuid_reg cpuid = reverse_cpuid[i];
Reviewed-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
