Re: [PATCH UPDATE] x86: ignore spurious faults

Andi Kleen
2008-01-25T09:12:06Z

On Friday 25 January 2008 09:38:38 Nick Piggin wrote:
> On Friday 25 January 2008 19:15, Jan Beulich wrote:
> > Actually, another thought: permitting (and handling) spurious faults for
> > kernel mappings conflicts with NMI handling, i.e. great care would be
> > needed to ensure the NMI path cannot touch any such mapping. So
> > even the present Xen/Linux Dom0 implementation may have some
> > (perhaps unlikely) problems here, and it would get worse if we added
> > e.g. a virtual watchdog NMI (something I am considering, which would
> > then extend the problem to DomU-s).
>
> Can you explain how they conflict?

NMI is blocked by the hardware until IRET and when a page fault happens inside
the NMI handler the early IRET unblocks it and then NMIs can nest, which
will lead to stack corruption.

-Andi