linux-kernel - Re: [PATCH] x86: set Pentium M as PAE capable

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Message-ID: <20140225113524.GA23256@pd.tnic>
Date:	Tue, 25 Feb 2014 12:35:24 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Chris Bainbridge <chris.bainbridge@...il.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: set Pentium M as PAE capable

On Tue, Feb 25, 2014 at 02:45:57AM -0800, H. Peter Anvin wrote:
> On 02/24/2014 10:01 PM, Chris Bainbridge wrote:
> >Pentium M is PAE capable but does not indicate so in the CPUID response.
> >This is an issue now that some distributions are no longer shipping
> >non-PAE kernels (those distributions no longer boot on Pentium M). This
> >small patch fixes the issue by forcing the PAE capability on Pentium M.
> >
> >For more discussion see https://bugs.launchpad.net/baltix/+bug/930447
> >
> 
> 1. This patch doesn't match the discussion in the link.
> 2. You would have to also enable this in the cpu testing code in
>    arch/x86/boot.
> 3. At the very least we need to print a serious warning that the CPU
>    is being run outside its specifications.  I have no personal
>    information about why this CPUID bit was disabled, but it could be
>    that it was discovered in testing that it didn't work correctly in
>    all circumstances (e.g. high temperature.)  This is very much "use
>    at your own risk..."; you could get data corruption or even
>    hardware damage.
> 
>    We should probably also taint the kernel.

Right, I was about to say that. And since there's no special bit for
running "out-of-spec", we could probably repurpose

TAINT_UNSAFE_SMP - 'S' - SMP with CPUs not designed for SMP.

to

TAINT_UNSAFE_OUT_OF_SPEC (the letter S fits still) and add that taint
everytime we're enforcing functionality against doctor's orders, so to
speak. :-)

Hmm.

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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