Re: [PATCH v4 9/9] KVM: x86: LAM: Expose LAM CPUID to user space VMM

Robert Hoo
2023-02-21T07:26:31Z

On Tue, 2023-02-21 at 13:47 +0800, Binbin Wu wrote:
> On 2/9/2023 10:40 AM, Robert Hoo wrote:
> > LAM feature is enumerated by (EAX=07H, ECX=01H):EAX.LAM[bit26].
> >
> > Signed-off-by: Robert Hoo <robert.hu@linux.intel.com>
> > Reviewed-by: Jingqi Liu <jingqi.liu@intel.com>
> > ---
> > arch/x86/kvm/cpuid.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> > index b14653b61470..79f45cbe587e 100644
> > --- a/arch/x86/kvm/cpuid.c
> > +++ b/arch/x86/kvm/cpuid.c
> > @@ -664,7 +664,7 @@ void kvm_set_cpu_caps(void)
> >
> > kvm_cpu_cap_mask(CPUID_7_1_EAX,
> > F(AVX_VNNI) | F(AVX512_BF16) | F(CMPCCXADD) |
> > F(AMX_FP16) |
> > - F(AVX_IFMA)
> > + F(AVX_IFMA) | F(LAM)
>
> Do we allow to expose the LAM capability to guest when host kernel
> disabled LAM feature (e.g. via clearcpuid)?

No
>
> May be it should be handled similarly as LA57.
>
You mean expose LAM to guest based on HW capability rather than host
status?
Why is LA57 exposure like this? unlike most features.

Without explicit rationality, I would tend to follow most conventions.