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

From: John Allen
Date: Thu Aug 17 2023 - 14:21:55 EST


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