[PATCH v2 03/15] KVM: x86: Refresh CPUID on writes to MSR_IA32_XSS

Yang Weijiang
2022-11-25T06:10:15Z

Updated CPUID.0xD.0x1, which reports the current required storage size
of all features enabled via XCR0 | XSS, when the guest's XSS is modified.

Note, KVM does not yet support any XSS based features, i.e. supported_xss
is guaranteed to be zero at this time.

Co-developed-by: Zhang Yi Z <yi.z.zhang@linux.intel.com>
Signed-off-by: Zhang Yi Z <yi.z.zhang@linux.intel.com>
Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
---
arch/x86/kvm/cpuid.c | 16 +++++++++++++---
arch/x86/kvm/x86.c | 6 ++++--
2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 6b5912578edd..85e3df6217af 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -272,9 +272,19 @@ static void __kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu, struct kvm_cpuid_e
best->ebx = xstate_required_size(vcpu->arch.xcr0, false);

best = cpuid_entry2_find(entries, nent, 0xD, 1);
- if (best && (cpuid_entry_has(best, X86_FEATURE_XSAVES) ||
- cpuid_entry_has(best, X86_FEATURE_XSAVEC)))
- best->ebx = xstate_required_size(vcpu->arch.xcr0, true);
+ if (best) {
+ if (cpuid_entry_has(best, X86_FEATURE_XSAVES) ||
+ cpuid_entry_has(best, X86_FEATURE_XSAVEC)) {
+ u64 xstate = vcpu->arch.xcr0 | vcpu->arch.ia32_xss;
+
+ best->ebx = xstate_required_size(xstate, true);
+ }
+
+ if (!cpuid_entry_has(best, X86_FEATURE_XSAVES)) {
+ best->ecx = 0;
+ best->edx = 0;
+ }
+ }

best = __kvm_find_kvm_cpuid_features(vcpu, entries, nent);
if (kvm_hlt_in_guest(vcpu->kvm) && best &&
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 16726b44061b..888a153e32bc 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3685,8 +3685,10 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
*/
if (data & ~kvm_caps.supported_xss)
return 1;
- vcpu->arch.ia32_xss = data;
- kvm_update_cpuid_runtime(vcpu);
+ if (vcpu->arch.ia32_xss != data) {
+ vcpu->arch.ia32_xss = data;
+ kvm_update_cpuid_runtime(vcpu);
+ }
break;
case MSR_SMI_COUNT:
if (!msr_info->host_initiated)
--
2.27.0