Re: [patch 1/2] x86_64 page fault NMI-safe

H. Peter Anvin
2010-07-15T23:43:05Z

On 07/15/2010 04:23 PM, Linus Torvalds wrote:
> On Thu, Jul 15, 2010 at 4:20 PM, H. Peter Anvin <hpa@zytor.com> wrote:
>> On 07/15/2010 03:58 PM, Andi Kleen wrote:
>>>> Why do we force IST use for NMI, btw? Maybe we shouldn't, and just use
>>>> the normal kernel stack mechanisms?
>>>
>>> If you don't use IST the SYSCALL entry is racy during the window
>>> when RSP is not set up yet (same for MCE etc.)
>>>
>>
>> Right, the kernel stack is not ready.
>
> Well, it may not be ready for the _current_ NMI handler, but if we're
> going to do a stack switch in sw on NMI anyway... ?
>

No, the problem is that without IST it'll try to drop the NMI stack
frame itself *on the user stack*.

-hpa

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