[RFC PATCH v3 3/8] KVM: x86: SVM: Pass through shadow stack MSRs

[John Allen <john.allen@xxxxxxx>]

If kvm supports shadow stack, pass through shadow stack MSRs to improve
guest performance.

Signed-off-by: John Allen <john.allen@xxxxxxx>
---
v3:
  - Conditionally pass through MSRs depending on both host and guest
    shadow stack support.
---
 arch/x86/kvm/svm/svm.c | 26 ++++++++++++++++++++++++++
 arch/x86/kvm/svm/svm.h |  2 +-
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 1ac5b51c3f2c..dd67f435cd33 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -140,6 +140,13 @@ static const struct svm_direct_access_msrs {
 	{ .index = X2APIC_MSR(APIC_TMICT),		.always = false },
 	{ .index = X2APIC_MSR(APIC_TMCCT),		.always = false },
 	{ .index = X2APIC_MSR(APIC_TDCR),		.always = false },
+	{ .index = MSR_IA32_U_CET,                      .always = false },
+	{ .index = MSR_IA32_S_CET,                      .always = false },
+	{ .index = MSR_IA32_INT_SSP_TAB,                .always = false },
+	{ .index = MSR_IA32_PL0_SSP,                    .always = false },
+	{ .index = MSR_IA32_PL1_SSP,                    .always = false },
+	{ .index = MSR_IA32_PL2_SSP,                    .always = false },
+	{ .index = MSR_IA32_PL3_SSP,                    .always = false },
 	{ .index = MSR_INVALID,				.always = false },
 };
 
@@ -1205,6 +1212,25 @@ static inline void init_vmcb_after_set_cpuid(struct kvm_vcpu *vcpu)
 		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_SYSENTER_EIP, 1, 1);
 		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_SYSENTER_ESP, 1, 1);
 	}
+
+	if (kvm_cpu_cap_has(X86_FEATURE_SHSTK)) {
+		bool shstk_enabled = guest_cpuid_has(vcpu, X86_FEATURE_SHSTK);
+
+		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_U_CET,
+				     shstk_enabled, shstk_enabled);
+		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_S_CET,
+				     shstk_enabled, shstk_enabled);
+		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_INT_SSP_TAB,
+				     shstk_enabled, shstk_enabled);
+		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_PL0_SSP,
+				     shstk_enabled, shstk_enabled);
+		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_PL1_SSP,
+				     shstk_enabled, shstk_enabled);
+		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_PL2_SSP,
+				     shstk_enabled, shstk_enabled);
+		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_PL3_SSP,
+				     shstk_enabled, shstk_enabled);
+	}
 }
 
 static void init_vmcb(struct kvm_vcpu *vcpu)
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 800ca1776b59..f824dde86e96 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	46
+#define MAX_DIRECT_ACCESS_MSRS	53
 #define MSRPM_OFFSETS	32
 extern u32 msrpm_offsets[MSRPM_OFFSETS] __read_mostly;
 extern bool npt_enabled;
-- 
2.39.1