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

Andi Kleen
2010-07-15T23:48:23Z

On Thu, Jul 15, 2010 at 04:23:20PM -0700, 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... ?

The CPU written initial stack frame would still go on the wrong stack.

-Andi

--
ak@linux.intel.com -- Speaking for myself only.