Messages in this thread | | | Date | Mon, 21 Apr 2008 11:47:56 -0400 | From | Mathieu Desnoyers <> | Subject | Re: [RFC PATCH] x86 NMI-safe INT3 and Page Fault (v5) |
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* H. Peter Anvin (hpa@zytor.com) 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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