lkml.org 
[lkml]   [2010]   [Sep]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] x86, nmi: workaround sti; hlt race vs nmi; intr
From
Date

On 27.09.2010, at 11:13, Alexander Graf wrote:

>
> On 27.09.2010, at 10:38, Avi Kivity wrote:
>
>> On 09/19/2010 06:28 PM, Avi Kivity wrote:
>>> On machines without monitor/mwait we use an sti; hlt sequence to atomically
>>> enable interrupts and put the cpu to sleep. The sequence uses the "interrupt
>>> shadow" property of the sti instruction: interrupts are enabled only after
>>> the instruction following sti has been executed. This means an interrupt
>>> cannot happen in the middle of the sequence, which would leave us with
>>> the interrupt processed but the cpu halted.
>>>
>>> The interrupt shadow, however, can be broken by an nmi; the following
>>> sequence
>>>
>>> sti
>>> nmi ... iret
>>> # interrupt shadow disabled
>>> intr ... iret
>>> hlt
>>>
>>> puts the cpu to sleep, even though the interrupt may need additional processing
>>> after the hlt (like scheduling a task).
>>>
>>> sti is explicitly documented not to force an interrupt shadow; though many
>>> processors do inhibit nmi immediately after sti.
>>>
>>> Avoid the race by checking, during an nmi, if we hit the safe halt sequence.
>>> If we did, increment the instruction pointer past the hlt instruction; this
>>> allows an immediately following interrupt to return to a safe place.
>>>
>>> Signed-off-by: Avi Kivity<avi@redhat.com>
>>
>> Ping.
>
> Wow, this is incredibly ugly :). Can't we just mask NMIs when the interrupt shadow is active?

Yeah, that's me writing without thinking. So this means that the race can also happen on real hardware?


Alex



\
 
 \ /
  Last update: 2010-09-27 20:11    [W:0.227 / U:22.468 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site