[RFC PATCH 6/7] 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>
---
 arch/x86/include/asm/svm.h |  1 +
 arch/x86/kvm/svm/sev.c     | 12 ++++++++++--
 arch/x86/kvm/svm/svm.c     |  1 +
 arch/x86/kvm/svm/svm.h     |  2 +-
 4 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
index 0361626841bc..b98c2a1087c0 100644
--- a/arch/x86/include/asm/svm.h
+++ b/arch/x86/include/asm/svm.h
@@ -625,5 +625,6 @@ 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 a5e72b2c94aa..55730055ee4c 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2418,8 +2418,13 @@ static void sev_es_sync_from_ghcb(struct vcpu_svm *svm)
 
 	svm->vmcb->save.cpl = ghcb_get_cpl_if_valid(ghcb);
 
-	if (ghcb_xcr0_is_valid(ghcb)) {
-		vcpu->arch.xcr0 = ghcb_get_xcr0(ghcb);
+	if (ghcb_xcr0_is_valid(ghcb) || ghcb_xss_is_valid(ghcb)) {
+		if (ghcb_xcr0_is_valid(ghcb))
+			vcpu->arch.xcr0 = ghcb_get_xcr0(ghcb);
+
+		if (ghcb_xss_is_valid(ghcb))
+			vcpu->arch.ia32_xss = ghcb_get_xss(ghcb);
+
 		kvm_update_cpuid_runtime(vcpu);
 	}
 
@@ -2988,6 +2993,9 @@ static void sev_es_init_vmcb(struct vcpu_svm *svm)
 		if (guest_cpuid_has(&svm->vcpu, X86_FEATURE_RDTSCP))
 			svm_clr_intercept(svm, INTERCEPT_RDTSCP);
 	}
+
+	if (kvm_caps.supported_xss)
+		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_XSS, 1, 1);
 }
 
 void sev_init_vmcb(struct vcpu_svm *svm)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index f40d3df2c1be..b474c7e57139 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -141,6 +141,7 @@ static const struct svm_direct_access_msrs {
 	{ .index = MSR_IA32_PL1_SSP,                    .always = false },
 	{ .index = MSR_IA32_PL2_SSP,                    .always = false },
 	{ .index = MSR_IA32_PL3_SSP,                    .always = false },
+	{ .index = MSR_IA32_XSS,                        .always = false },
 	{ .index = MSR_INVALID,				.always = false },
 };
 
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index c1c3e090ff9d..ad89b1dbe62d 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -29,7 +29,7 @@
 #define	IOPM_SIZE PAGE_SIZE * 3
 #define	MSRPM_SIZE PAGE_SIZE * 2
 
-#define MAX_DIRECT_ACCESS_MSRS	53
+#define MAX_DIRECT_ACCESS_MSRS	54
 #define MSRPM_OFFSETS	32
 extern u32 msrpm_offsets[MSRPM_OFFSETS] __read_mostly;
 extern bool npt_enabled;
-- 
2.34.3