Messages in this thread | | | Date | Tue, 29 Nov 2005 18:57:30 +0530 | From | Vivek Goyal <> | Subject | Re: [Fastboot] Re: [PATCH & RFC] kdump and stack overflows |
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On Mon, Nov 28, 2005 at 11:29:29AM -0700, Eric W. Biederman wrote: > Fernando Luis Vazquez Cao <fernando@intellilink.co.jp> writes: > > > On Mon, 2005-11-28 at 06:39 -0700, Eric W. Biederman wrote: > >> Fernando Luis Vazquez Cao <fernando@intellilink.co.jp> writes: > > > Regarding the stack overflow audit of the nmi path, we have the problem > > that both nmi_enter and nmi_exit in do_nmi (see code below) make heavy > > use of "current" indirectly (specially through the kernel preemption > > code). > > Ok. I wonder if it would be saner to simply replace the nmi trap > handler on the crash dump path? >
Sounds interesting.
> >> I believe we have a separate interrupt stack that > >> should help but.. > > Yes, when using 4K stacks we have a separate interrupt stack that should > > help, but I am afraid that crash dumping is about being paranoid. > > Oh I agree. If we had a private 4K stack for the nmi handler we > would not need to worry about overflow in that case.
Having private 4K stack makes sense as crash_nmi_callback() itself requires quite some space on stack. If one has enabled CONFIG_4KSTACKS, then we use separate interrupt stack and we are probably safe from stack overflows but otherwise we need it.
> (baring > nmi happening during nmis) Hmm. Is there anything to keep > us doing something bad in that case? > > I guess as long as we don't clear the high bit of port 0x70 we > should be reasonably safe from the nmi firing multiple times.
Are you referring to port 0x23 for IMCR register.
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