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

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Message-ID: <ZN1FW7krxOVs9uA8@google.com>
Date:   Wed, 16 Aug 2023 14:53:31 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Binbin Wu <binbin.wu@...ux.intel.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        pbonzini@...hat.com, chao.gao@...el.com, kai.huang@...el.com,
        David.Laight@...lab.com, robert.hu@...ux.intel.com,
        guang.zeng@...el.com
Subject: Re: [PATCH v10 9/9] KVM: x86: Expose LAM feature to userspace VMM

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)

On Wed, Jul 19, 2023, Binbin Wu wrote:
> From: Robert Hoo <robert.hu@...ux.intel.com>
> 
> 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@...ux.intel.com>
> Signed-off-by: Binbin Wu <binbin.wu@...ux.intel.com>
> Reviewed-by: Jingqi Liu <jingqi.liu@...el.com>
> Reviewed-by: Chao Gao <chao.gao@...el.com>
> Reviewed-by: Kai Huang <kai.huang@...el.com>
> Tested-by: Xuelian Guo <xuelian.guo@...el.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 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
>