Messages in this thread | | | Subject | Re: [PATCH 5/5] stack overflow safe kdump (2.6.15-i386) - private nmi stack | From | Fernando Luis Vazquez Cao <> | Date | Wed, 25 Jan 2006 16:22:30 +0900 |
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On Fri, 2006-01-20 at 08:19 -0500, Vivek Goyal wrote: > On Thu, Jan 19, 2006 at 01:43:14PM +0900, Fernando Luis Vazquez Cao wrote: > > On Tue, 2006-01-17 at 20:51 -0500, Vivek Goyal wrote: > > > > > > Does not work for 8K stacks. Also we are switching the stack all the > > > time for NMI. I am not sure if that is really required (performance?). > > Yes, it does not work for 8K stacks, but this is something premeditated. > > Since private stacks for interrupts are only used when 4KSTACKS > > is enabled I felt that to be consistent it should be the same in > > the NMI's case. Anyway if it is deemed correct (I agree it is desirable) > > I could implement it. > > > > Regarding the impact in performance, note that when we use 4K stacks we > > are switching stacks _every_ time an interrupt occurs. I do not see why > > we should not do the same for NMIs. Specially since the cost of > > switching stacks is relatively small when compared to the cost of > > executing the NMI watchdog's handler. > > > > > Can't it be made to work both for 4K and 8K stack. And switch to reserved > > > stack on NMI, only if crash has happened. > > Yes, it could be done, but I think it is safer to use a private stack > > all the time, so that the NMI handler does not contribute to an eventual > > stack overflow. I would like to avoid the case of the the stack > > overflowing inside the NMI handler. > > Ok. Then we are looking at an entirely different problem and that is avoid > stack overflows for NMI for 4K stacks in general and not necessarily a > crash dump specific code hardening. Exactly.
Fernando
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