KVM: x86: SVM: don't set VMLOAD/VMSAVE intercepts on vCPU reset

Commit adc2a23734ac ("KVM: nSVM: improve SYSENTER emulation on AMD"),
made init_vmcb set vmload/vmsave intercepts unconditionally,
and relied on svm_vcpu_after_set_cpuid to clear them when possible.

However init_vmcb is also called when the vCPU is reset, and it is
not followed by another call to svm_vcpu_after_set_cpuid because
the CPUID is already set.  This mistake makes the VMSAVE/VMLOAD intercept
to be set when it is not needed, and harms performance of the nested
guest.

Extract the relevant parts of svm_vcpu_after_set_cpuid so that they
can be called again on reset.

Fixes: adc2a23734ac ("KVM: nSVM: improve SYSENTER emulation on AMD")
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 34 insertions, 27 deletions

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 270a091d57b0..53d593016be5 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1161,6 +1161,38 @@ static void svm_recalc_instruction_intercepts(struct kvm_vcpu *vcpu,
 	}
 }
 
+static inline void init_vmcb_after_set_cpuid(struct kvm_vcpu *vcpu)
+{
+	struct vcpu_svm *svm = to_svm(vcpu);
+
+	if (guest_cpuid_is_intel(vcpu)) {
+		/*
+		 * We must intercept SYSENTER_EIP and SYSENTER_ESP
+		 * accesses because the processor only stores 32 bits.
+		 * For the same reason we cannot use virtual VMLOAD/VMSAVE.
+		 */
+		svm_set_intercept(svm, INTERCEPT_VMLOAD);
+		svm_set_intercept(svm, INTERCEPT_VMSAVE);
+		svm->vmcb->control.virt_ext &= ~VIRTUAL_VMLOAD_VMSAVE_ENABLE_MASK;
+
+		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_SYSENTER_EIP, 0, 0);
+		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_SYSENTER_ESP, 0, 0);
+	} else {
+		/*
+		 * If hardware supports Virtual VMLOAD VMSAVE then enable it
+		 * in VMCB and clear intercepts to avoid #VMEXIT.
+		 */
+		if (vls) {
+			svm_clr_intercept(svm, INTERCEPT_VMLOAD);
+			svm_clr_intercept(svm, INTERCEPT_VMSAVE);
+			svm->vmcb->control.virt_ext |= VIRTUAL_VMLOAD_VMSAVE_ENABLE_MASK;
+		}
+		/* No need to intercept these MSRs */
+		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_SYSENTER_EIP, 1, 1);
+		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_SYSENTER_ESP, 1, 1);
+	}
+}
+
 static void init_vmcb(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
@@ -1307,6 +1339,7 @@ static void init_vmcb(struct kvm_vcpu *vcpu)
 	}
 
 	svm_hv_init_vmcb(svm->vmcb);
+	init_vmcb_after_set_cpuid(vcpu);
 
 	vmcb_mark_all_dirty(svm->vmcb);
 
@@ -4043,33 +4076,7 @@ static void svm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 			kvm_request_apicv_update(vcpu->kvm, false,
 						 APICV_INHIBIT_REASON_NESTED);
 	}
-
-	if (guest_cpuid_is_intel(vcpu)) {
-		/*
-		 * We must intercept SYSENTER_EIP and SYSENTER_ESP
-		 * accesses because the processor only stores 32 bits.
-		 * For the same reason we cannot use virtual VMLOAD/VMSAVE.
-		 */
-		svm_set_intercept(svm, INTERCEPT_VMLOAD);
-		svm_set_intercept(svm, INTERCEPT_VMSAVE);
-		svm->vmcb->control.virt_ext &= ~VIRTUAL_VMLOAD_VMSAVE_ENABLE_MASK;
-
-		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_SYSENTER_EIP, 0, 0);
-		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_SYSENTER_ESP, 0, 0);
-	} else {
-		/*
-		 * If hardware supports Virtual VMLOAD VMSAVE then enable it
-		 * in VMCB and clear intercepts to avoid #VMEXIT.
-		 */
-		if (vls) {
-			svm_clr_intercept(svm, INTERCEPT_VMLOAD);
-			svm_clr_intercept(svm, INTERCEPT_VMSAVE);
-			svm->vmcb->control.virt_ext |= VIRTUAL_VMLOAD_VMSAVE_ENABLE_MASK;
-		}
-		/* No need to intercept these MSRs */
-		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_SYSENTER_EIP, 1, 1);
-		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_SYSENTER_ESP, 1, 1);
-	}
+	init_vmcb_after_set_cpuid(vcpu);
 }
 
 static bool svm_has_wbinvd_exit(void)