linux-kernel - Re: [RFC][PATCH 02/22] x86,mmx

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Date:   Thu, 4 Nov 2021 19:00:43 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, jpoimboe@...hat.com,
        mark.rutland@....com, dvyukov@...gle.com, seanjc@...gle.com,
        pbonzini@...hat.com, mbenes@...e.cz
Subject: Re: [RFC][PATCH 02/22] x86,mmx_32: Remove .fixup usage

On Thu, Nov 04, 2021 at 05:47:31PM +0100, Peter Zijlstra wrote:
> This code puts an exception table entry on the "PREFIX" instruction to
> overwrite it with a jmp.d8 when it triggers an exception. Except of
> course, our code is no longer writable, also SMP.
> 
> Replace it with ALTERNATIVE, the novel
> 
> XXX: arguably we should just delete this code

Yah, might as well.

Wikipedia says the last AMD CPU which supports 3DNow is A8-3870K which
is family 0x11, i.e.,

1. a real rarity
2. it is pretty much obsolete
3. even if not, it can do AMD64
4. and even if people who have it, wanna run 32-bit, they can use the
normal memcpy, i.e., CONFIG_X86_USE_3DNOW=n should work there

In our case, it is a bit different, though:

config X86_USE_3DNOW
        def_bool y
        depends on (MCYRIXIII || MK7 || MGEODE_LX) && !UML

MK7 is K7 - that is practically dead.

The only thing I have no clue about are those cyrix and geode things and
whether they're still actively used in some embedded gunk.

-- 
Regards/Gruss,
    Boris.

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