linux-kernel - Re: [PATCH v4 1/6] x86: move ZMM exclusion list into CPU feature flag

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Message-ID: <20250210213705.GD348261@sol.localdomain>
Date: Mon, 10 Feb 2025 13:37:05 -0800
From: Eric Biggers <ebiggers@...nel.org>
To: Borislav Petkov <bp@...en8.de>
Cc: linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
	x86@...nel.org, linux-block@...r.kernel.org,
	Ard Biesheuvel <ardb@...nel.org>, Keith Busch <kbusch@...nel.org>,
	Kent Overstreet <kent.overstreet@...ux.dev>,
	"Martin K . Petersen" <martin.petersen@...cle.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH v4 1/6] x86: move ZMM exclusion list into CPU feature flag

On Mon, Feb 10, 2025 at 10:17:10PM +0100, Borislav Petkov wrote:
> On Mon, Feb 10, 2025 at 01:01:03PM -0800, Eric Biggers wrote:
> > I see that cpu_feature_enabled() uses code patching while boot_cpu_has() does
> > not.  All these checks occur once at module load time, though, so code patching
> > wouldn't be beneficial.
> 
> We want to convert all code to use a single interface for testing CPU features
> - cpu_feature_enabled() - and the implementation shouldn't be important to
> users - it should just work.
> 
> Since you're adding new code, you might as well use the proper interface. As
> to converting crypto/ and the rest of the tree, that should happen at some
> point... eventually...

Well, it's new code in a function that already has a bunch of boot_cpu_has()
checks.  I don't really like leaving around random inconsistencies.  If there is
a new way to do it, we should just update it everywhere.

I'll also note that boot_cpu_has() is missing a comment that says it is
deprecated (if it really is).

- Eric