Re: [patch 1/2] x86_64 page fault NMI-safe

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

* Andi Kleen (andi@firstfloor.org) wrote:
> > or similar. Wouldn't that be nice to have as a capability?
> 
> It means the NMI watchdog would get useless if these areas
> become common.
> 
> Again I suspect all of this is not really needed anyways if 
> vmalloc_sync_all() works properly. That would solve the original
> problem Mathieu was trying to solve for per_cpu data. The rule
> would be just to call vmalloc_sync_all() properly when changing
> per CPU data too.

Yep, that would solve the page fault in nmi problem altogether without adding
complexity.

> 
> In fact I'm pretty sure it worked originally. Perhaps it regressed?

I'd first ask the obvious to Perf authors: does perf issue vmalloc_sync_all()
between percpu data allocation and tracing activation ? The generic ring buffer
library I posted last week does it already as a precaution for this very
specific reason (making sure NMIs never trigger page faults).

Thanks,

Mathieu

> 
> -Andi
> -- 
> ak@linux.intel.com -- Speaking for myself only.

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com