[PATCH v2 6/9] KVM: SVM: Add MSR_IA32_XSS to the GHCB for hypervisor kernel

[John Allen <john.allen@xxxxxxx>]

When a guest issues a cpuid instruction for Fn0000000D_x0B
(CetUserOffset), KVM will intercept and need to access the guest
MSR_IA32_XSS value. For SEV-ES, this is encrypted and needs to be
included in the GHCB to be visible to the hypervisor.

Signed-off-by: John Allen <john.allen@xxxxxxx>
---
v2:
  - Omit passing through XSS as this has already been properly
    implemented in a26b7cd22546 ("KVM: SEV: Do not intercept
    accesses to MSR_IA32_XSS for SEV-ES guests") 
---
 arch/x86/include/asm/svm.h | 1 +
 arch/x86/kvm/svm/sev.c     | 9 +++++++--
 arch/x86/kvm/svm/svm.h     | 1 +
 3 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
index 728c98175b9c..44cd41e2fb68 100644
--- a/arch/x86/include/asm/svm.h
+++ b/arch/x86/include/asm/svm.h
@@ -673,5 +673,6 @@ DEFINE_GHCB_ACCESSORS(sw_exit_info_1)
 DEFINE_GHCB_ACCESSORS(sw_exit_info_2)
 DEFINE_GHCB_ACCESSORS(sw_scratch)
 DEFINE_GHCB_ACCESSORS(xcr0)
+DEFINE_GHCB_ACCESSORS(xss)
 
 #endif
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index f06f9e51ad9d..c3060d2068eb 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2458,8 +2458,13 @@ static void sev_es_sync_from_ghcb(struct vcpu_svm *svm)
 
 	svm->vmcb->save.cpl = kvm_ghcb_get_cpl_if_valid(svm, ghcb);
 
-	if (kvm_ghcb_xcr0_is_valid(svm)) {
-		vcpu->arch.xcr0 = ghcb_get_xcr0(ghcb);
+	if (kvm_ghcb_xcr0_is_valid(svm) || kvm_ghcb_xss_is_valid(svm)) {
+		if (kvm_ghcb_xcr0_is_valid(svm))
+			vcpu->arch.xcr0 = ghcb_get_xcr0(ghcb);
+
+		if (kvm_ghcb_xss_is_valid(svm))
+			vcpu->arch.ia32_xss = ghcb_get_xss(ghcb);
+
 		kvm_update_cpuid_runtime(vcpu);
 	}
 
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 0741fa049fd7..eb9c9e337c43 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -723,5 +723,6 @@ DEFINE_KVM_GHCB_ACCESSORS(sw_exit_info_1)
 DEFINE_KVM_GHCB_ACCESSORS(sw_exit_info_2)
 DEFINE_KVM_GHCB_ACCESSORS(sw_scratch)
 DEFINE_KVM_GHCB_ACCESSORS(xcr0)
+DEFINE_KVM_GHCB_ACCESSORS(xss)
 
 #endif
-- 
2.40.1