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    SubjectRe: [PATCH 5/5] stack overflow safe kdump (2.6.15-i386) - private nmi stack
    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.


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