Re: [PATCH v10 9/9] KVM: x86: Expose LAM feature to userspace VMM

[Binbin Wu]

On 8/17/2023 5:53 AM, Sean Christopherson wrote:
> s/Expose/Advertise
>
> And I would add an "enable" in there somehwere, because to Kai's point earlier in
> the series about kvm_cpu_cap_has(), the guest can't actually use LAM until this
> patch.  Sometimes we do just say "Advertise", but typically only for features
> where there's not virtualization support, e.g. AVX instructions where the guest
> can use them irrespective of what KVM says it supports.
>
> This?
>
> KVM: x86: Advertise and enable LAM (user and supervisor)
It looks good to me. Thanks.

> On Wed, Jul 19, 2023, Binbin Wu wrote:
> > From: Robert Hoo <robert.hu@xxxxxxxxxxxxxxx>
> >
> > LAM feature is enumerated by CPUID.7.1:EAX.LAM[bit 26].
> > Expose the feature to userspace as the final step after the following
> > supports:
> > - CR4.LAM_SUP virtualization
> > - CR3.LAM_U48 and CR3.LAM_U57 virtualization
> > - Check and untag 64-bit linear address when LAM applies in instruction
> >    emulations and VMExit handlers.
> >
> > Exposing SGX LAM support is not supported yet. SGX LAM support is enumerated
> > in SGX's own CPUID and there's no hard requirement that it must be supported
> > when LAM is reported in CPUID leaf 0x7.
> >
> > Signed-off-by: Robert Hoo <robert.hu@xxxxxxxxxxxxxxx>
> > Signed-off-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>
> > Reviewed-by: Jingqi Liu <jingqi.liu@xxxxxxxxx>
> > Reviewed-by: Chao Gao <chao.gao@xxxxxxxxx>
> > Reviewed-by: Kai Huang <kai.huang@xxxxxxxxx>
> > Tested-by: Xuelian Guo <xuelian.guo@xxxxxxxxx>
> > ---
> >   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 7ebf3ce1bb5f..21d525b01d45 100644
> > --- a/arch/x86/kvm/cpuid.c
> > +++ b/arch/x86/kvm/cpuid.c
> > @@ -645,7 +645,7 @@ void kvm_set_cpu_caps(void)
> >   	kvm_cpu_cap_mask(CPUID_7_1_EAX,
> >   		F(AVX_VNNI) | F(AVX512_BF16) | F(CMPCCXADD) |
> >   		F(FZRM) | F(FSRS) | F(FSRC) |
> > -		F(AMX_FP16) | F(AVX_IFMA)
> > +		F(AMX_FP16) | F(AVX_IFMA) | F(LAM)
> >   	);
> >   
> >   	kvm_cpu_cap_init_kvm_defined(CPUID_7_1_EDX,
> > --
> > 2.25.1