linux-kernel - [PATCH v3 4/5] KVM: SVM: Add MSR_IA32_XSS to the GHCB for hypervisor kernel

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Message-ID: <20250806204510.59083-5-john.allen@amd.com>
Date: Wed, 6 Aug 2025 20:45:09 +0000
From: John Allen <john.allen@....com>
To: <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>, <x86@...nel.org>,
	<seanjc@...gle.com>, <pbonzini@...hat.com>, <dave.hansen@...el.com>
CC: <rick.p.edgecombe@...el.com>, <mlevitsk@...hat.com>,
	<weijiang.yang@...el.com>, <chao.gao@...el.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>, <hpa@...or.com>, <mingo@...hat.com>,
	<tglx@...utronix.de>, <thomas.lendacky@....com>, John Allen
	<john.allen@....com>
Subject: [PATCH v3 4/5] KVM: SVM: Add MSR_IA32_XSS to the GHCB for hypervisor kernel

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@....com>
---
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")
v3:
  - Move guest kernel GHCB_ACCESSORS definition to new series.
---
 arch/x86/kvm/svm/sev.c | 9 +++++++--
 arch/x86/kvm/svm/svm.h | 1 +
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 3f20f6eb1ef6..2905a62e7bf2 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -3239,8 +3239,13 @@ 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);
+
 		vcpu->arch.cpuid_dynamic_bits_dirty = true;
 	}
 
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index dabd69d6fd15..b189647d8389 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -925,5 +925,6 @@ 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
-- 
2.34.1