Message-ID: <4C3F9DF2.807@zytor.com>
Date: Thu, 15 Jul 2010 16:46:58 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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Subject: Re: [patch 1/2] x86_64 page fault NMI-safe
References: <20100714222115.GA30122@Krystal>	<AANLkTikLG4xVYfvuMtbuzsqcnzo1ut4dFAm6piqy2Lh7@mail.gmail.com>	<AANLkTin21xBD-BFY4ZX2BPRFnT5-LkgGugvWsvTEP4Mr@mail.gmail.com>	<AANLkTil4LYSjS88P2CopOVi3Ty9pxwFPsaw0328KlPSu@mail.gmail.com>	<20100715183153.GA9276@Krystal>	<AANLkTilfXUtQznSzOmO9ecoaviIt62Hv6jdUOMSRLdrF@mail.gmail.com>	<AANLkTimAn0uMpeYKctO0qxM6nwbfev3RHARLZIbf991k@mail.gmail.com>	<20100715220117.GA1499@Krystal>	<AANLkTinL3S3iMSoP0fb6bxn9IY62OmytBtbqCKy9CZk2@mail.gmail.com>	<AANLkTinOTwnSNgwX7PnalhzwWMjwie0Xk_Lnrn_0bLzz@mail.gmail.com>	<20100715225844.GA25420@one.firstfloor.org>	<4C3F97A5.4020107@zytor.com>	<AANLkTinLg2Xx0x6jrKkK_em6dA0cEfujnV3XIZ6I10jI@mail.gmail.com>	<4C3F9CBB.3080300@zytor.com> <AANLkTik7LzRAo7dq9MurwVY1Pn2tTkmItYxBA5nrpV2S@mail.gmail.com>
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On 07/15/2010 04:44 PM, Linus Torvalds wrote:
> On Thu, Jul 15, 2010 at 4:41 PM, H. Peter Anvin <hpa@zytor.com> wrote:
>>
>> No, the problem is that without IST it'll try to drop the NMI stack
>> frame itself *on the user stack*.
> 
> Oh, because SS has already been cleared, but rsp still points to the
> user stack? Ok, that does seem insurmountable.
> 

Well, SS doesn't matter for 64 bits, but yes, RSP still points to the
user stack.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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