[PATCH v3 07/21] KVM:x86: Refresh CPUID on write to guest MSR_IA32_XSS

Yang Weijiang
2023-05-11T07:13:46Z

Update CPUID(EAX=0DH,ECX=1) when the guest's XSS is modified.
CPUID(EAX=0DH,ECX=1).EBX reports current required storage size for all
features enabled via XCR0 | XSS so that guest can allocate correct xsave
buffer.

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 | 7 +++++--
arch/x86/kvm/x86.c | 6 ++++--
2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 123bf8b97a4b..cbb1b8a65502 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -277,8 +277,11 @@ static void __kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu, struct kvm_cpuid_e

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);
+ cpuid_entry_has(best, X86_FEATURE_XSAVEC))) {
+ u64 xstate = vcpu->arch.xcr0 | vcpu->arch.ia32_xss;
+
+ best->ebx = xstate_required_size(xstate, true);
+ }

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 33a780fe820b..ab3360a10933 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3776,8 +3776,10 @@ 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