linux-kernel - Re: [PATCH 2/6] x86: KVM: Enable AMX-FP16 CPUID and expose it to guest

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aa7f6efc-de4c-c5f6-fb5f-ef514e4513a3@redhat.com>
Date:   Wed, 2 Nov 2022 19:16:37 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        Jiaxi Chen <jiaxi.chen@...ux.intel.com>, kvm@...r.kernel.org
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        seanjc@...gle.com, ndesaulniers@...gle.com,
        alexandre.belloni@...tlin.com, peterz@...radead.org,
        jpoimboe@...nel.org, chang.seok.bae@...el.com,
        pawan.kumar.gupta@...ux.intel.com, babu.moger@....com,
        jmattson@...gle.com, sandipan.das@....com, tony.luck@...el.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, fenghua.yu@...el.com,
        keescook@...omium.org, jane.malalane@...rix.com, nathan@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/6] x86: KVM: Enable AMX-FP16 CPUID and expose it to
 guest

On 11/2/22 19:14, Dave Hansen wrote:
>>   
>>   	kvm_cpu_cap_mask(CPUID_7_1_EAX,
>> -		F(AVX_VNNI) | F(AVX512_BF16) | F(CMPCCXADD)
>> +		F(AVX_VNNI) | F(AVX512_BF16) | F(CMPCCXADD) | F(AMX_FP16)
>>   	);
>>   
>>   	kvm_cpu_cap_mask(CPUID_D_1_EAX,
>
> KVM folks, is the idea that every feature that is enumerated to a guest
> needs to be in one of these masks?  Or is there something special about
> the features in these masks?

Yes, all features are vetted manually to see whether they require new 
MSRs and the like.  Therefore, anything that userspace can set in the 
guest's CPUID must be in the list.

Paolo