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

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Message-ID: <CALCETrUvbnkVTKDVtgnXYPGiXDY621sY9MbOrCvjmpqG8xz-wA@mail.gmail.com>
Date:	Fri, 6 Mar 2015 14:28:31 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...nel.org>, Oleg Nesterov <oleg@...hat.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Borislav Petkov <bp@...e.de>, Pekka Riikonen <priikone@....fi>,
	Rik van Riel <riel@...hat.com>,
	Suresh Siddha <sbsiddha@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"Yu, Fenghua" <fenghua.yu@...el.com>,
	Quentin Casasnovas <quentin.casasnovas@...cle.com>
Subject: Re: [PATCH 1/1] x86/fpu: math_state_restore() should not blindly
 disable irqs

On Fri, Mar 6, 2015 at 2:00 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Fri, Mar 6, 2015 at 11:23 AM, Andy Lutomirski <luto@...capital.net> wrote:
>>
>> Please don't.  IMO it's really nice that we don't use trap gates at
>> all on x86_64, and I find the conditional_sti thing much nicer than
>> having to audit all of the entry code to see whether it's safe to run
>> it with IRQs on.
>
> So I'm not sure I see much difference, but I'd certainly be ok with
> just moving the "conditional_sti()" up unconditionally to be the first
> thing in do_device_not_available().

I'd be fine with that.  The important difference is that it's after swapgs.

--Andy

>
> The point being that we still *not* just randomly enable interrupts
> because we decide that the callers are wrong.
>
>                        Linus



-- 
Andy Lutomirski
AMA Capital Management, LLC
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