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Date: Tue, 22 Apr 2014 11:51:27 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Brian Gerst <brgerst@gmail.com>
CC: Andrew Lutomirski <amluto@gmail.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
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        Arjan van de Ven <arjan.van.de.ven@intel.com>,
        Alexandre Julliard <julliard@winehq.com>,
        Andi Kleen <andi@firstfloor.org>, Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH] x86-64: espfix for 64-bit mode *PROTOTYPE*
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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