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

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Date:	Thu, 23 Feb 2012 23:27:33 +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 02:11:48PM -0800, Linus Torvalds wrote:
> On Thu, Feb 23, 2012 at 1:52 PM, Willy Tarreau <w@....eu> wrote:
> >
> > I would test this too, but apart from ensuring my kernel still boots,
> > how do I ensure the patches do really fix what the ought to fix ? I
> > must admit I didn't catch the initial issue they were supposed to fix
> > unfortunately :-/
> 
> Almost nobody did.
> 
> This only happens on modern CPU's that support the new AES-NI
> instructions, and only with a 32-bit kernel (although the very
> unlikely preemption issues can happen on x86-64 too). And you need to
> have the AES instructions called from interrupts, which probably only
> happens with the mac80211 wireless networking stack.
> 
> And even then you need WPA2 to trigger it (I guess AES is sometimes
> used with "extended WPA1" too, but I dunno).
> 
> So it's not impossible to trigger, but you do need to have a fairly
> recent CPU that happily runs in 64-bit mode, and install a 32-bit
> system on it. And it needs to use the right wireless setup.

OK so indeed I will only be able to check that it boots :-/

> It's possible that the right solution for really older kernels is just
> to say that AES_NI depends on X86_64.

Might be a good idea !

Thanks for the explanation,
Willy

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