linux-kernel - Re: [PATCH] x86, nmi: workaround sti; hlt race vs nmi; intr

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Message-Id: <1640BBFF-4E7C-4F56-BF53-AD290C353F64@suse.de>
Date:	Mon, 27 Sep 2010 11:36:46 +0200
From:	Alexander Graf <agraf@...e.de>
To:	Avi Kivity <avi@...hat.com>
Cc:	x86@...nel.org, LKML List <linux-kernel@...r.kernel.org>,
	KVM list <kvm@...r.kernel.org>,
	Joerg Roedel <joerg.roedel@....com>,
	Wilfred Yu <wilfred.yu@...el.com>
Subject: Re: [PATCH] x86, nmi: workaround sti; hlt race vs nmi; intr


On 27.09.2010, at 11:27, Avi Kivity wrote:

> On 09/27/2010 11:22 AM, Alexander Graf wrote:
>> On 27.09.2010, at 11:17, Avi Kivity wrote:
>> 
>> >  On 09/27/2010 11:15 AM, Alexander Graf wrote:
>> >>  >
>> >>  >   Wow, this is incredibly ugly :). Can't we just mask NMIs when the interrupt shadow is active?
>> >
>> >  I plan to do that, for all the code that's out there relying on on STI interrupt shadow masking NMIs.
>> >
>> >>  Yeah, that's me writing without thinking. So this means that the race can also happen on real hardware?
>> >>
>> >
>> >  Yes.  At least on documented hardware.  Some (most? all?) hardware does mask NMIs after STI.
>> 
>> If all hardware masks NMIs after STI, wouldn't it be better to update the spec and declare KVM buggy for injecting NMIs there?
>> 
> 
> I don't have write permissions for the spec.  If you can verify that all existing and future hardware will mask NMI after STI and convince the spec owners to update the specifications, I'm all for it; it's certainly a cleaner solution.

*shrug* I don't have permissions for that either, but we can CC people who might get into touch with some who can.


Alex

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