linux-kernel - Re: [PATCH 01/11] mm: Introduce a function to check for virtualization protection features

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Date:   Wed, 28 Jul 2021 18:28:01 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Tom Lendacky <thomas.lendacky@....com>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        iommu@...ts.linux-foundation.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-graphics-maintainer@...are.com,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        kexec@...ts.infradead.org, linux-fsdevel@...r.kernel.org,
        Andi Kleen <ak@...ux.intel.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH 01/11] mm: Introduce a function to check for
 virtualization protection features

On Wed, Jul 28, 2021 at 02:17:27PM +0100, Christoph Hellwig wrote:
> So common checks obviously make sense, but I really hate the stupid
> multiplexer.  Having one well-documented helper per feature is much
> easier to follow.

We had that in x86 - it was called cpu_has_<xxx> where xxx is the
feature bit. It didn't scale with the sheer amount of feature bits that
kept getting added so we do cpu_feature_enabled(X86_FEATURE_XXX) now.

The idea behind this is very similar - those protected guest flags
will only grow in the couple of tens range - at least - so having a
multiplexer is a lot simpler, I'd say, than having a couple of tens of
helpers. And those PATTR flags should have good, readable names, btw.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette