On Tue, Aug 30, 2022 at 4:39 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
>
> On Tue, Aug 30, 2022, Jim Mattson wrote:
> > Intel enumerates support for PSFD in CPUID.(EAX=7,ECX=2):EDX.PSFD[bit
> > 0]. Report support for this feature in KVM if it is available on the
> > host.
> >
> > Presumably, this feature bit, like its AMD counterpart, is not welcome
> > in cpufeatures.h, so add a local definition of this feature in KVM.
> >
> > Signed-off-by: Jim Mattson <jmattson@xxxxxxxxxx>
> > ---
> > arch/x86/kvm/cpuid.c | 23 +++++++++++++++++------
> > 1 file changed, 17 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> > index 07be45c5bb93..b5af9e451bef 100644
> > --- a/arch/x86/kvm/cpuid.c
> > +++ b/arch/x86/kvm/cpuid.c
> > @@ -62,6 +62,7 @@ u32 xstate_required_size(u64 xstate_bv, bool compacted)
> > * This one is tied to SSB in the user API, and not
> > * visible in /proc/cpuinfo.
> > */
> > +#define KVM_X86_FEATURE_PSFD 0 /* Predictive Store Forwarding Disable */
>
> I believe we can use "enum kvm_only_cpuid_leafs" to handle this. E.g.
>
> enum kvm_only_cpuid_leafs {
> CPUID_12_EAX = NCAPINTS,
> CPUID_7_2_EDX,
> NR_KVM_CPU_CAPS,
>
> NKVMCAPINTS = NR_KVM_CPU_CAPS - NCAPINTS,
> };
>
> then the intended use of KVM_X86_FEATURE_*
>
> #define KVM_X86_FEATURE_PSFD KVM_X86_FEATURE(CPUID_7_2_EDX, 0)
>
> I _think_ we can then define an arbitrary word for X86_FEATURE_PSFD, e.g.
>
> #define X86_FEATURE_PSFD (NKVMCAPINTS*32+0)
We may run afoul of reverse_cpuid_check(), depending on usage.
> and then wire up the translation:
>
> static __always_inline u32 __feature_translate(int x86_feature)
> {
> if (x86_feature == X86_FEATURE_SGX1)
> return KVM_X86_FEATURE_SGX1;
> else if (x86_feature == X86_FEATURE_SGX2)
> return KVM_X86_FEATURE_SGX2;
> else if (x86_feature == X86_FEATURE_PSFD)
> return KVM_X86_FEATURE_PSFD;
>
> return x86_feature;
> }
>
> I believe/hope that allows us to use at least cpuid_entry_override(). Open coding
> masking of specific registers was a mess that I don't want to repeat.
Maybe we can plead for a bit in word 11?
