On Wed, Apr 07, 2021, Ramakrishna Saripalli wrote: > From: Ramakrishna Saripalli <rk.saripalli@xxxxxxx> > > Expose Predictive Store Forwarding capability to guests. Technically KVM is advertising the capability to userspace, e.g. userspace can expose the feature to the guest without this patch. > Guests enable or disable PSF via SPEC_CTRL MSR. At a (very) quick glance, this requires extra enabling in guest_has_spec_ctrl_msr(), otherwise a vCPU with PSF but not the existing features will not be able to set MSR_IA32_SPEC_CTRL.PSFD. That raises a question: should KVM do extra checks for PSFD on top of the "throw noodles at the wall and see what sticks" approach of kvm_spec_ctrl_test_value()? The noodle approach is there to handle the mess of cross-vendor features/bits, but that doesn't seem to apply to PSFD. > Signed-off-by: Ramakrishna Saripalli <rk.saripalli@xxxxxxx> > --- > arch/x86/kvm/cpuid.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c > index 6bd2f8b830e4..9c4af0fef6d7 100644 > --- a/arch/x86/kvm/cpuid.c > +++ b/arch/x86/kvm/cpuid.c > @@ -448,6 +448,8 @@ void kvm_set_cpu_caps(void) > kvm_cpu_cap_set(X86_FEATURE_INTEL_STIBP); > if (boot_cpu_has(X86_FEATURE_AMD_SSBD)) > kvm_cpu_cap_set(X86_FEATURE_SPEC_CTRL_SSBD); > + if (boot_cpu_has(X86_FEATURE_AMD_PSFD)) > + kvm_cpu_cap_set(X86_FEATURE_AMD_PSFD); This is unnecessary, it's handled by the F(AMD_PSFD). The above features have special handling to enumerate their Intel equivalent. > kvm_cpu_cap_mask(CPUID_7_1_EAX, > F(AVX_VNNI) | F(AVX512_BF16) > @@ -482,7 +484,7 @@ void kvm_set_cpu_caps(void) > kvm_cpu_cap_mask(CPUID_8000_0008_EBX, > F(CLZERO) | F(XSAVEERPTR) | > F(WBNOINVD) | F(AMD_IBPB) | F(AMD_IBRS) | F(AMD_SSBD) | F(VIRT_SSBD) | > - F(AMD_SSB_NO) | F(AMD_STIBP) | F(AMD_STIBP_ALWAYS_ON) > + F(AMD_SSB_NO) | F(AMD_STIBP) | F(AMD_STIBP_ALWAYS_ON) | F(AMD_PSFD) > ); > > /* > -- > 2.25.1 >
