linux-kernel - Re: [PATCH 0/5] i387: stable kernel backport

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Date:	Thu, 23 Feb 2012 23:49:27 +0100
From:	Willy Tarreau <w@....eu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"H. Peter Anvin" <hpa@...or.com>, stable@...r.kernel.org,
	Raphael Prevost <raphael@...o.asia>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/5] i387: stable kernel backport

On Thu, Feb 23, 2012 at 02:38:42PM -0800, Linus Torvalds wrote:
> On Thu, Feb 23, 2012 at 2:27 PM, Willy Tarreau <w@....eu> wrote:
> >
> > OK so indeed I will only be able to check that it boots :-/
> 
> Well, we could do some trivial test-harness that just forces the issue
> with regular timer interrupts (and even without AES-NI). I think Peter
> talked about that when we were trying to hunt it down - but I think he
> was then able to reproduce the problem without anything special and we
> dropped it.
> 
> Essentially, just doing something like
> 
>     if (irq_fpu_usable()) {
>         kernel_fpu_begin();
>         kernel_fpu_end();
>     }
> 
> in do_irq() and do_softirq() would stress-test things even without
> wireless, and even without AES-NI.

Interesting...

> You'd still need an x86-32 machine to test on, because x86-64 was
> immune to this issue.
> 
> But yeah, the impact of this seems to be small enough that for older
> kernels (which are likely used on older systems for maintenance
> anyway) disabling AES-NI on x86-32 really might be the way to go.

I agree. I don't know anybody using AES-NI on purpose on older x86-32
systems!

Willy

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