linux-kernel - Re: [PATCH 1/2] Documentation/x86: Add the AMX enabling example

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Date:   Wed, 24 Aug 2022 11:33:58 +0700
From:   Bagas Sanjaya <bagasdotme@...il.com>
To:     "Chang S. Bae" <chang.seok.bae@...el.com>
Cc:     dave.hansen@...el.com, len.brown@...el.com, tony.luck@...el.com,
        rafael.j.wysocki@...el.com, reinette.chatre@...el.com,
        dan.j.williams@...el.com, corbet@....net, pbonzini@...hat.com,
        kvm@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] Documentation/x86: Add the AMX enabling example

On Thu, Jun 16, 2022 at 02:22:09PM -0700, Chang S. Bae wrote: 
> +  1. **Check the feature availability**. AMX_TILE is enumerated in CPUID
> +     leaf 7, sub-leaf 0, bit 24 of EDX. If available, ``/proc/cpuinfo``
> +     shows ``amx_tile`` in the flag entry of the CPUs.  Given that, the
> +     kernel may have set XSTATE component 18 in the XCR0 register. But a
> +     user needs to ensure the kernel support via the ARCH_GET_XCOMP_SUPP
> +     option::
> +
> +        #include <asm/prctl.h>
> +        #include <sys/syscall.h>
> +	#include <stdio.h>
> +        #include <unistd.h>
> +
> +        #define ARCH_GET_XCOMP_SUPP  0x1021
> +
> +        #define XFEATURE_XTILECFG    17
> +        #define XFEATURE_XTILEDATA   18
> +        #define XFEATURE_MASK_XTILE ((1 << XFEATURE_XTILECFG) | (1 << XFEATURE_XFILEDATA))
> +
> +        unsigned long features;
> +        long rc;
> +
> +        ...
> +
> +        rc = syscall(SYS_arch_prctl, ARCH_GET_XCOMP_SUPP, &features);
> +
> +        if (!rc && features & XFEATURE_MASK_XTILE == XFEATURE_MASK_XTILE)
> +            printf("AMX is available.\n");
> +

nit: stdio include line isn't aligned with the rest of code.

Otherwise LGTM (no new warnings).

Reviewed-by: Bagas Sanjaya <bagasdotme@...il.com>

-- 
An old man doll... just what I always wanted! - Clara

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