linux-kernel - Re: [PATCH] x86/fpu: Use consistent test for X86_FEATURE

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Date:   Wed, 3 Feb 2021 07:40:07 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Borislav Petkov <bp@...e.de>,
        "Chang S. Bae" <chang.seok.bae@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     x86@...nel.org, luto@...nel.org, mingo@...nel.org,
        tglx@...utronix.de, len.brown@...el.com, ravi.v.shankar@...el.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/fpu: Use consistent test for X86_FEATURE_XSAVES

On 2/3/21 3:23 AM, Borislav Petkov wrote:
>> -/*
>> - * 'XSAVES' implies two different things:
>> - * 1. saving of supervisor/system state
>> - * 2. using the compacted format
>> - *
>> - * Use this function when dealing with the compacted format so
>> - * that it is obvious which aspect of 'XSAVES' is being handled
>> - * by the calling code.
> @dhansen, are you still hung up on that "obvious aspect" or can we kill
> this?

I still want the compacted-format handling code to be marked.  You can
do that with new comments:

	/* Note: XSAVES always uses compacted format: */
	if (boot_cpu_has(X86_FEATURE_XSAVES)) {

or, leave it as-is:

	if (using_compacted_format()) {
	...

Otherwise, we assume that every human being that looks at this code
*KNOWS* that XSAVES==compacted.  That's not a great assumption.