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

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Message-ID: <e7113e249fa0fc1f259408c9f97655ec199dba5e.camel@xry111.site>
Date:   Wed, 21 Jun 2023 21:47:36 +0800
From:   Xi Ruoyao <xry111@...111.site>
To:     Borislav Petkov <bp@...en8.de>
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, 2023-06-21 at 15:46 +0200, Borislav Petkov wrote:
> 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?

Oh s**t, I'm completely stupid :(.

-- 
Xi Ruoyao <xry111@...111.site>
School of Aerospace Science and Technology, Xidian University