linux-kernel - Re: A question about prefetchw detection in "x86/asm: Cleanup prefetch primitives"

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Message-ID: <20230621134645.GIZJL/Rf1IdeLMQGl2@fat_crate.local>
Date:   Wed, 21 Jun 2023 15:46:45 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Xi Ruoyao <xry111@...111.site>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: A question about prefetchw detection in "x86/asm: Cleanup
 prefetch primitives"

On Wed, Jun 21, 2023 at 09:19:34PM +0800, Xi Ruoyao wrote:
> On Wed, 2023-06-21 at 15:09 +0200, Borislav Petkov wrote:
> > On Wed, Jun 21, 2023 at 09:06:51PM +0800, Xi Ruoyao wrote:
> > > I think it's not an issue in the kernel itself, but announcing
> > > 3dnowprefetch in /proc/cpuinfo for an old Intel CPU w/o real prefetchw
> > > implementation seems problematic (to me).
> > 
> > And this is a problem because?
> 
> If a code generator parses /proc/cpuinfo for CPU capabilities, it may
> generates a no-op prefetchw instead of prefetcht0 as a fallback.

Err, go back.

That code snippet you pasted, did you see where that comes from?

A function called init_amd().

Now, is Intel hardware and SDM PREFETCHW text at all relevant here?

-- 
Regards/Gruss,
    Boris.

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