linux-kernel - Re: i686 quirk for AMD Geode

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Date:	Thu, 12 Nov 2009 06:40:04 +0100
From:	Willy Tarreau <w@....eu>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Matt Thrailkill <matt.thrailkill@...il.com>,
	Ingo Molnar <mingo@...e.hu>, Pavel Machek <pavel@....cz>,
	Avi Kivity <avi@...hat.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Matteo Croce <technoboy85@...il.com>,
	Sven-Haegar Koch <haegar@...net.de>,
	linux-kernel@...r.kernel.org
Subject: Re: i686 quirk for AMD Geode

On Wed, Nov 11, 2009 at 09:31:26PM -0800, H. Peter Anvin wrote:
> On 11/11/2009 09:27 PM, Willy Tarreau wrote:
> > 
> > Right. However we just noticed that with the KVM emulator, you
> > can make it loop for a long time if you feed it with prefixes
> > only. For instance, write a function which does zillions of 0x66
> > (data size prefix) then return (0xC3) : 66 66 66 ... 66 C3.
> > 
> > This is typically the sort of things we must be very careful about
> > in emulators, because we don't want users to steal large amounts
> > of system CPU time doing nothing.
> > 
> 
> That is a (serious) bug in the KVM interpreter, and indeed the exact
> kind of issues interpreters tend to have... which is why I'd like one
> piece of code with one set of bugs, and more eyeballs on that one piece
> of code so they can be fixed.

Well, I could try to work on a fix (basically the same principle as in
mine, with prefix flags), but I simply don't know how to test the code.
I've never experimented with KVM yet and learned it embeds an emulator
for the first time a few days ago in this thread :-/ If it's easy to
make use of it, I'm not opposed to try.

Willy

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