linux-kernel - Re: [PATCH] x86-64: espfix for 64-bit mode *PROTOTYPE*

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Message-ID: <5356BA2F.2030007@zytor.com>
Date:	Tue, 22 Apr 2014 11:51:27 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Brian Gerst <brgerst@...il.com>
CC:	Andrew Lutomirski <amluto@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Alexander van Heukelum <heukelum@...tmail.fm>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Arjan van de Ven <arjan.van.de.ven@...el.com>,
	Alexandre Julliard <julliard@...ehq.com>,
	Andi Kleen <andi@...stfloor.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] x86-64: espfix for 64-bit mode *PROTOTYPE*

On 04/22/2014 11:17 AM, Brian Gerst wrote:
>>
>> That is the entry condition that we have to deal with.  The fact that
>> the switch to the IST is unconditional is what makes ISTs hard to deal with.
> 
> Right, that is why you switch away from the IST as soon as possible,
> copying the data that is already pushed there to another stack so it
> won't be overwritten by a recursive fault.
> 

That simply will not work if you can take a #GP due to the "safe" MSR
functions from NMI and #MC context, which would be my main concern.

	-hpa

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