linux-kernel - Re: [PATCH v4 4/6] x86: KVM: Advertise AVX-VNNI-INT8 CPUID to user space

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: <Y3e+PNvvuuT3aCmb@google.com>
Date:   Fri, 18 Nov 2022 17:17:48 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Jiaxi Chen <jiaxi.chen@...ux.intel.com>
Cc:     kvm@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org,
        hpa@...or.com, pbonzini@...hat.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, nathan@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 4/6] x86: KVM: Advertise AVX-VNNI-INT8 CPUID to user
 space

On Fri, Nov 18, 2022, Jiaxi Chen wrote:
> AVX-VNNI-INT8 is a new set of instructions in the latest Intel platform
> Sierra Forest, aims for the platform to have superior AI capabilities.
> This instruction multiplies the individual bytes of two unsigned or
> unsigned source operands, then adds and accumulates the results into the
> destination dword element size operand.
> 
> The bit definition:
> CPUID.(EAX=7,ECX=1):EDX[bit 4]
> 
> This CPUID is exposed to user space. Besides, there is no other VMX
> control for this instruction.
> 
> Signed-off-by: Jiaxi Chen <jiaxi.chen@...ux.intel.com>
> ---
>  arch/x86/kvm/cpuid.c         | 5 ++++-
>  arch/x86/kvm/reverse_cpuid.h | 5 +++++
>  2 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 5726afb2d14c..e2b8e5485474 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -660,6 +660,9 @@ void kvm_set_cpu_caps(void)
>  		F(AVX_VNNI) | F(AVX512_BF16) | F(CMPCCXADD) | F(AMX_FP16) |
>  		F(AVX_IFMA));
>  
> +	kvm_cpu_cap_init_scattered(CPUID_7_1_EDX,

Ah, this is going to be confusing and potentially error prone.  AVX_VNNI_INT8
isn't actually scattered, i.e. kvm_cpu_cap_init_scattered() is poorly named.  And
using SF() would be _really_ broken as boot_cpu_has() would consume garbage and
potentially leak kernel state to userspace.

To address these issue and also document how to add KVM-only features, can you
slot in the two attached patches at the begining of this series?

Thanks!

> +		F(AVX_VNNI_INT8));

Terminators on a separate line please.

>  	kvm_cpu_cap_mask(CPUID_D_1_EAX,
>  		F(XSAVEOPT) | F(XSAVEC) | F(XGETBV1) | F(XSAVES) | f_xfd
>  	);

View attachment "0001-KVM-x86-Add-BUILD_BUG_ON-to-detect-bad-usage-of-scat.patch" of type "text/x-diff" (1711 bytes)

View attachment "0002-KVM-x86-Update-KVM-only-leaf-handling-to-allow-for-1.patch" of type "text/x-diff" (3597 bytes)