[v2,2/2] KVM: SVM: Disable RDTSCP and TSC_AUX MSR intercepts when V_TSC_AUX is present

Commit Message

Babu Moger April 19, 2022, 8:54 p.m. UTC

The TSC_AUX virtualization feature allows AMD SEV-ES guests to securely use
TSC_AUX (auxiliary time stamp counter data) in the RDTSCP and RDPID
instructions. The TSC_AUX value is set using the WRMSR instruction to the
TSC_AUX MSR (0xC0000103). It is read by the RDMSR, RDTSCP and RDPID
instructions. If the read/write of the TSC_AUX MSR is intercepted, then
RDTSCP and RDPID must also be intercepted when TSC_AUX virtualization
is present. However, the RDPID instruction can't be intercepted. This means
that when TSC_AUX virtualization is present, RDTSCP and TSC_AUX MSR
read/write must not be intercepted for SEV-ES (or SEV-SNP) guests.

Signed-off-by: Babu Moger <[e-mail]>
---
v2:
No changes from v1.

v1:
https://lore.kernel.org/kvm/164937947781.1047063.9230786680311460912.stgit@bmoger-ubuntu/

 arch/x86/kvm/svm/sev.c |    8 ++++++++
 arch/x86/kvm/svm/svm.c |    1 +
 arch/x86/kvm/svm/svm.h |    2 +-
 3 files changed, 10 insertions(+), 1 deletion(-)

Patch

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 537aaddc852f..b0ead47c85e5 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2922,6 +2922,14 @@  void sev_es_init_vmcb(struct vcpu_svm *svm)
 	set_msr_interception(vcpu, svm->msrpm, MSR_IA32_LASTBRANCHTOIP, 1, 1);
 	set_msr_interception(vcpu, svm->msrpm, MSR_IA32_LASTINTFROMIP, 1, 1);
 	set_msr_interception(vcpu, svm->msrpm, MSR_IA32_LASTINTTOIP, 1, 1);
+
+	if (boot_cpu_has(X86_FEATURE_V_TSC_AUX) &&
+	    (guest_cpuid_has(&svm->vcpu, X86_FEATURE_RDTSCP) ||
+	     guest_cpuid_has(&svm->vcpu, X86_FEATURE_RDPID))) {
+		set_msr_interception(vcpu, svm->msrpm, MSR_TSC_AUX, 1, 1);
+		if (guest_cpuid_has(&svm->vcpu, X86_FEATURE_RDTSCP))
+			svm_clr_intercept(svm, INTERCEPT_RDTSCP);
+	}
 }
 
 void sev_es_vcpu_reset(struct vcpu_svm *svm)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index bd4c64b362d2..526dc1be1c3c 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -101,6 +101,7 @@  static const struct svm_direct_access_msrs {
 	{ .index = MSR_EFER,				.always = false },
 	{ .index = MSR_IA32_CR_PAT,			.always = false },
 	{ .index = MSR_AMD64_SEV_ES_GHCB,		.always = true  },
+	{ .index = MSR_TSC_AUX,				.always = false },
 	{ .index = MSR_INVALID,				.always = false },
 };
 
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index f77a7d2d39dd..da701edec93b 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	20
+#define MAX_DIRECT_ACCESS_MSRS	21
 #define MSRPM_OFFSETS	16
 extern u32 msrpm_offsets[MSRPM_OFFSETS] __read_mostly;
 extern bool npt_enabled;