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

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Message-ID: <d595fad7-0d78-bdab-ee66-f1eb1d9488ed@linux.intel.com>
Date:   Thu, 17 Aug 2023 09:59:24 +0800
From:   Binbin Wu <binbin.wu@...ux.intel.com>
To:     Sean Christopherson <seanjc@...gle.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



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@...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
>>