Re: kmemcheck: OS boot failed because NMI handlers access the memory tracked by kmemcheck

[Vegard Nossum]

On 03/17/2014 10:51 AM, Michal Hocko wrote:
> On Mon 17-03-14 17:19:33, Xishi Qiu wrote:
> > OS boot failed when set cmdline kmemcheck=1. The reason is that
> > NMI handlers will access the memory from kmalloc(), this will cause
> > page fault, because memory from kmalloc() is tracked by kmemcheck.
> >
> > watchdog_nmi_enable()
> > 	perf_event_create_kernel_counter()
> > 		perf_event_alloc()
> > 			event = kzalloc(sizeof(*event), GFP_KERNEL);
>
> Where is this path called from an NMI context?
>
> Your trace bellow points at something else and it doesn't seem to
> allocate any memory either. It looks more like x86_perf_event_update
> sees an invalid perf_event or something like that...

It's not important that the kzalloc() is called from NMI context, it's 
important that the memory that was allocated is touched (read/written) 
from NMI context.

I'm currently looking into the possibility of handling recursive faults 
in kmemcheck (using the approach outlined by peterz; see 
https://lkml.org/lkml/2014/2/26/141).


Vegard
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