linux-kernel - Re: [tip: x86/fpu] x86/arch_prctl: Add AMX feature numbers as ABI constants

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Message-ID: <ffeee8d3-3b92-fe21-1b5e-1c17444a6a8b@intel.com>
Date:   Wed, 22 Mar 2023 15:02:04 -0700
From:   "Chang S. Bae" <chang.seok.bae@...el.com>
To:     <linux-kernel@...r.kernel.org>,
        <linux-tip-commits@...r.kernel.org>,
        "Dave Hansen" <dave.hansen@...ux.intel.com>
CC:     Tony Luck <tony.luck@...el.com>, <x86@...nel.org>
Subject: Re: [tip: x86/fpu] x86/arch_prctl: Add AMX feature numbers as ABI
 constants

On 3/22/2023 1:14 PM, tip-bot2 for Chang S. Bae wrote:
> The following commit has been merged into the x86/fpu branch of tip:
> 
> x86/arch_prctl: Add AMX feature numbers as ABI constants
> 
> Each distinct XSAVE feature has a number assigned to it.  Among other
> things, the number determines the ordering of features in the XSAVE
> buffer and is also used to generate XSAVE bitmasks like the value
> for XCR0.
> 
> AMX state is dynamically enabled by the architecture-specific prctl().
> This prctl() takes one XSAVE feature number as an argument.  However, the
> feature numbers are not defined in any readily available userspace headers.
> The means that each userspace app trying to use dynamic feature prctl()s
> will likely end up defining their own constants for each feature.
> 
> Since these feature numbers are a part of the uabi, expose them in the
> prctl() uabi header.  Save everyone the trouble of looking them up and
> defining their own.
> 
> [ dhansen: expand changelog a bit ]

Sorry, it looks like I was not diligent enough to explain what those 
numbers are and that they are now part of the ABI.

Thank you for the write-up.

Chang