[PATCH v14 02/13] KVM: x86: Refresh CPUID on writes to MSR_IA32_XSS

[Yang Weijiang]

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.zh...@linux.intel.com>
Signed-off-by: Zhang Yi Z <yi.z.zh...@linux.intel.com>
Signed-off-by: Yang Weijiang <weijiang.y...@intel.com>
---
 arch/x86/include/asm/kvm_host.h |  1 +
 arch/x86/kvm/cpuid.c            | 21 ++++++++++++++++++---
 arch/x86/kvm/x86.c              |  7 +++++--
 3 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index d44858b69353..1620a2cca781 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -611,6 +611,7 @@ struct kvm_vcpu_arch {
 
        u64 xcr0;
        u64 guest_supported_xcr0;
+       u64 guest_supported_xss;
 
        struct kvm_pio_request pio;
        void *pio_data;
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 06a278b3701d..2c737337f466 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -115,9 +115,24 @@ void kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu)
                best->ebx = xstate_required_size(vcpu->arch.xcr0, false);
 
        best = kvm_find_cpuid_entry(vcpu, 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;
+               }
+               vcpu->arch.guest_supported_xss =
+                       (((u64)best->edx << 32) | best->ecx) & supported_xss;
+
+       } else {
+               vcpu->arch.guest_supported_xss = 0;
+       }
 
        best = kvm_find_cpuid_entry(vcpu, KVM_CPUID_FEATURES, 0);
        if (kvm_hlt_in_guest(vcpu->kvm) && best &&
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index fce18a2537ea..0823bf1e2977 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3124,9 +3124,12 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct 
msr_data *msr_info)
                 * IA32_XSS[bit 8]. Guests have to use RDMSR/WRMSR rather than
                 * XSAVES/XRSTORS to save/restore PT MSRs.
                 */
-               if (data & ~supported_xss)
+               if (data & ~vcpu->arch.guest_supported_xss)
                        return 1;
-               vcpu->arch.ia32_xss = data;
+               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)
-- 
2.17.2