linux-kernel - Re: [PATCH 1/1] x86/fpu: math_state_restore() should not blindly disable irqs

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Message-ID: <CALCETrUBJyOc4bUJJUH7b=xAuDKRmo9YKs4QBDVSjd07UM4Sfw@mail.gmail.com>
Date:	Sun, 8 Mar 2015 07:38:19 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Fenghua Yu <fenghua.yu@...el.com>,
	Quentin Casasnovas <quentin.casasnovas@...cle.com>,
	Suresh Siddha <sbsiddha@...il.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Borislav Petkov <bp@...e.de>, Oleg Nesterov <oleg@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Pekka Riikonen <priikone@....fi>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] x86/fpu: math_state_restore() should not blindly
 disable irqs

On Sun, Mar 8, 2015 at 6:59 AM, Andy Lutomirski <luto@...capital.net> wrote:
> There's another problem, though:  We don't have a real stack pointer
> just after syscall and just before sysexit, and therefore we *must*
> use IST for anything that can happen while we still have
> user-controlled rsp.  That includes #DB, #NM, and #MC.

I think I faked myself out here.  Why do #DB and #BP use IST?  We
could remove a decent (large?) amount of crud if we changed that.

--Andy
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