linux-kernel - Re: [PATCH] x86, cpu: Fix X86_FEATURE

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Date:	Mon, 4 Oct 2010 13:47:27 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86, cpu: Fix X86_FEATURE_NOPL

On Mon, Oct 4, 2010 at 12:31 AM, Borislav Petkov <bp@...en8.de> wrote:
>
> ba0593bf553c450a03dbc5f8c1f0ff58b778a0c8 cleared the aforementioned
> cpuid bit only on 32-bit due to various problems with Virtual PC. This
> somehow got lost during the 32- + 64-bit merge so restore the feature
> bit on 64-bit. For that, set it explicitly for non-constant arguments of
> cpu_has(). Update comment for future reference.

I don't think this is right.

The cpu_has() logic depends not on x86-64, but on X86_P6_NOP.

Which has

        depends on X86_64
        depends on (MCORE2 || MPENTIUM4 || MPSC)

as its config rules, not just X86_64.

So I think your patch is bogus. It makes the current situation even
_more_ confusing than it is.

So what is it? Should we get rid of that odd X86_P6_NOP thing
entirely? Or should we use it consistently for the "this machine has
NOPL"? Should we always use P6_NOP for x86-64 and just remove the
"MCORE2 || MPENTIUM4 || MPSC" thing?

Whatever we do, I don't think this patch is the right one.

                   Linus
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