linux-kernel - Re: [PATCH v8 6/6] KVM: x86: Expose LAM feature to userspace VMM

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Date:   Tue, 16 May 2023 11:30:56 +0800
From:   Binbin Wu <binbin.wu@...ux.intel.com>
To:     "Huang, Kai" <kai.huang@...el.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     "robert.hu@...ux.intel.com" <robert.hu@...ux.intel.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "Gao, Chao" <chao.gao@...el.com>
Subject: Re: [PATCH v8 6/6] KVM: x86: Expose LAM feature to userspace VMM



On 5/12/2023 8:49 PM, Huang, Kai wrote:
> On Wed, 2023-05-10 at 14:06 +0800, 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.
>>
>> 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>
>> 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 123bf8b97a4b..fc8286f747ac 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(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,
> Per spec LAM supports SGX enclave mode too (chapter 6.8 INTEL SGX INTERACTIONS).
>
> Per my read, whether you can enable LAM57 or LAM48 can be determined by bit 8
> and 9 of CPUID.(EAX=12H, ECX=01H):EAX.  There are some special rule of whether
> LAM is applied to certain linear address too, i.e. per my read SECS.BASEADDR
> isn't subject to LAM in ECREATE.
This is considered when implement patch 5, but you remind me that I 
should add the materials to describe the handling of SGX system leaf 
functions in the chagelog.


>
> My first glance to expose LAM to guest's SGX enclave is just as simple as what
> you did here -- we just need to expose the two new bits to userspace in
> KVM_GET_SUPPORTED_CPUID.
>
> But I think this can be done in a separate series,
Yes, support LAM inside SGX enclave is not included in the inital 
enabling patch series.

>   especially as the spec
> doesn't say when LAM is available in CPUID(0x7, 0x1):EAX, it will be always
> available in CPUID(0x12, 0x1).EAX.
>
> But could you help to check the hardware hehaviour whether they will always
> appear together in CPUID?
For this part, I need furtuer investigation.
Will get back to you when I get the answer.