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

[Mathieu Desnoyers]

* H. Peter Anvin (hpa@xxxxxxxxx) wrote:
> Mathieu Desnoyers wrote:
>> Just to be clear : the added cost on normal interrupt return is to add a
>> supplementary test of the thread flags already loaded in registers and
>> a conditional branch. This is used to detect if we are nested over an
>> NMI handler. I doubt anyone ever notice an impact caused by this added
>> test/branch.
>
> Why the **** would you do this except in the handful of places where you 
> actually *could* be nested over an NMI handler (basically #MC, #DB and 
> INT3)?
>
> 	-hpa
>

There is also the page fault case. I think putting this test in
ret_from_exception would be both safe (it is executed for any
exception return) and fast (exceptions are rare).

Mathieu

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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