linux-kernel - Re: [PATCH] x86: Execute WP test after interrupts are enabled

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Date:	Tue, 25 Aug 2009 22:03:28 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Pekka Enberg <penberg@...helsinki.fi>,
	"H. Peter Anvin" <hpa@...or.com>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	linux-kernel@...r.kernel.org,
	Arnd Hannemann <hannemann@...s.rwth-aachen.de>,
	Brian Gerst <brgerst@...il.com>
Subject: Re: [PATCH] x86: Execute WP test after interrupts are enabled


* Pekka Enberg <penberg@...helsinki.fi> wrote:

> On Tue, Aug 25, 2009 at 10:53 PM, Jeremy Fitzhardinge<jeremy@...p.org> wrote:
> > On 08/25/09 12:38, Pekka Enberg wrote:
> >> On Tue, 2009-08-25 at 12:34 -0700, Jeremy Fitzhardinge wrote:
> >>
> >>> I don't think this is the real fix, and it seems a bit ugly. ?I'm OK
> >>> with it as a workaround, but I think it will end up getting reverted if
> >>> applied.
> >>>
> >> Yeah, I'm fine with that. It's just that we're really late in the
> >> release cycle now so I'd like to keep the fix as simple as possible.
> >
> > Yeah, that's fine, but I think something like this would be simpler.
> > Arnd, could you test it please?
> >
> > From: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
> > Date: Tue, 25 Aug 2009 12:47:17 -0700
> > Subject: [PATCH] xen: suppress WP test
> >
> > Xen always runs on CPUs which properly support WP enforcement in
> > privileged mode, so there's no need to test for it.
> >
> > This also works around a crash reported by Arnd Hannemann, though
> > I think its just a band-aid for that case.
> >
> > Reported-by: Arnd Hannemann <hannemann@...s.rwth-aachen.de>
> > Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
> > Cc: Pekka Enberg <penberg@...helsinki.fi>
> >
> > diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> > index 16d0d70..e5b903b 100644
> > --- a/arch/x86/xen/enlighten.c
> > +++ b/arch/x86/xen/enlighten.c
> > @@ -1069,6 +1069,7 @@ asmlinkage void __init xen_start_kernel(void)
> > ? ? ? ?/* set up basic CPUID stuff */
> > ? ? ? ?cpu_detect(&new_cpu_data);
> > ? ? ? ?new_cpu_data.hard_math = 1;
> > + ? ? ? new_cpu_data.wp_works_ok = 1;
> > ? ? ? ?new_cpu_data.x86_capability[0] = cpuid_edx(1);
> > ?#endif
> 
> Yeah, this is even better assuming it works. :-)
> 
> Acked-by: Pekka Enberg <penberg@...helsinki.fi>

yeah, we should do this one for .31.

	Ingo
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