Re: [RFC PATCH] x86 NMI-safe INT3 and Page Fault (v5)

[H. Peter Anvin]

Pavel Machek wrote:
> On Thu 2008-04-17 16:14:10, Mathieu Desnoyers wrote:
> > (hopefully finally CCing LKML) :)
> >
> > Implements an alternative iret with popf and return so trap and exception
> > handlers can return to the NMI handler without issuing iret. iret would cause
> > NMIs to be reenabled prematurely. x86_32 uses popf and far return. x86_64 has to
> > copy the return instruction pointer to the top of the previous stack, issue a
> > popf, loads the previous esp and issue a near return (ret).
>
> sounds expensive. Does it slow down normal loads?

It should *only* be used to return from NMI, #MC or INT3 (breakpoint), 
which should never happen in normal operation, and even then only when 
interrupting another NMI or #MC handler.

	-hpa

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