[PATCH 2/6] KVM: VMX: Passthrough MSR_IA32_PRED_CMD based purely on host+guest CPUID

Sean Christopherson
2023-03-22T01:16:07Z

Passthrough MSR_IA32_PRED_CMD based purely on whether or not the MSR is
supported and enabled, i.e. don't wait until the first write. There's no
benefit to deferred passthrough, and the extra logic only adds complexity.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/vmx/vmx.c | 16 +++-------------
1 file changed, 3 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index f777509ecf17..5c01c76c0d45 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2298,19 +2298,6 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
break;

wrmsrl(MSR_IA32_PRED_CMD, PRED_CMD_IBPB);
-
- /*
- * For non-nested:
- * When it's written (to non-zero) for the first time, pass
- * it through.
- *
- * For nested:
- * The handling of the MSR bitmap for L2 guests is done in
- * nested_vmx_prepare_msr_bitmap. We should not touch the
- * vmcs02.msr_bitmap here since it gets completely overwritten
- * in the merging.
- */
- vmx_disable_intercept_for_msr(vcpu, MSR_IA32_PRED_CMD, MSR_TYPE_W);
break;
case MSR_IA32_CR_PAT:
if (!kvm_pat_valid(data))
@@ -7743,6 +7730,9 @@ static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
vmx_set_intercept_for_msr(vcpu, MSR_IA32_XFD_ERR, MSR_TYPE_R,
!guest_cpuid_has(vcpu, X86_FEATURE_XFD));

+ if (boot_cpu_has(X86_FEATURE_IBPB))
+ vmx_set_intercept_for_msr(vcpu, MSR_IA32_PRED_CMD, MSR_TYPE_W,
+ !guest_has_pred_cmd_msr(vcpu));

set_cr4_guest_host_mask(vmx);

--
2.40.0.rc2.332.ga46443480c-goog