linux-kernel - Re: [PATCH] i386: improve double fault handling

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Message-Id: <4888467F.76E4.0078.0@novell.com>
Date:	Thu, 24 Jul 2008 08:08:15 +0100
From:	"Jan Beulich" <jbeulich@...ell.com>
To:	"Joerg Roedel" <joro@...tes.org>
Cc:	<mingo@...e.hu>, "Andi Kleen" <andi@...stfloor.org>,
	<tglx@...utronix.de>, <linux-kernel@...r.kernel.org>,
	<hpa@...or.com>
Subject: Re: [PATCH] i386: improve double fault handling

>>> Joerg Roedel <joro@...tes.org> 23.07.08 23:43 >>>
>On Fri, Jul 18, 2008 at 01:30:42PM +0100, Jan Beulich wrote:
>> Make the double fault handler use CPU-specific stacks. Add some
>> abstraction to simplify future change of other exception handlers to go
>> through task gates.
>
>What is the benefit of exception handlers going through task gates?
>Hardware task switches are not very well supported in virtualization
>(e.g. its has issues in KVM and is also not in Xen for a long time).

The main goal is to get to a different stack. While at present this is done
only for the double fault, I think generally NMI and MCE should also do
so, as they may be caused by a stack access (see x86-64, which runs
them on IST stacks), and hence continuing to run on that same stack
may not allow the exception to be handled.

Jan

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