Advertise support for WRMSRNS (WRMSR non-serializing) to userspace if the instruction is supported by the underlying CPU. From a virtualization perspective, the only difference between WRMSRNS and WRMSR is that VM-Exits due to WRMSRNS set EXIT_QUALIFICATION to '1'. WRMSRNS doesn't require a new enabling control, shares the same basic exit reason, and behaves the same as WRMSR with respect to MSR interception. WRMSR and WRMSRNS use the same basic exit reason (see Appendix C). For WRMSR, the exit qualification is 0, while for WRMSRNS it is 1. Don't do anything different when emulating WRMSRNS vs. WRMSR, as KVM can't do anything less, i.e. can't make emulation non-serializing. The motivation for the guest to use WRMSRNS instead of WRMSR is to avoid immediately serializing the CPU when the necessary serialization is guaranteed by some other mechanism, i.e. WRMSRNS being fully serializing isn't guest-visible, just less performant. Suggested-by: Xin Li (Intel) <xin@xxxxxxxxx> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> --- arch/x86/kvm/cpuid.c | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index 97a90689a9dc..ebecfe4bea1e 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -992,6 +992,7 @@ void kvm_set_cpu_caps(void) F(FZRM), F(FSRS), F(FSRC), + F(WRMSRNS), F(AMX_FP16), F(AVX_IFMA), F(LAM), -- 2.48.1.711.g2feabab25a-goog
