Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain supportto use NMI-safe methods

[H. Peter Anvin]

Linus Torvalds wrote:
> 
> On Mon, 15 Jun 2009, Ingo Molnar wrote:
>> A simple cr2 corruption would explain all those cc1 SIGSEGVs and 
>> other user-space crashes i saw, with sufficiently intense sampling - 
>> easily.
> 
> Note that we could work around the %cr2 issue, since any corruption is 
> always nicely "nested" (ie there are never any SMP issues with async 
> writes to the register).
> 
> So what we _could_ do is to have a magic value for %cr2, along with a "NMI 
> sequence count", and if we see that value, we just return (without doing 
> anything) from the page fault handler.
> 

Wouldn't it be simpler to just require the NMI handler to save and
restore %cr2 around any potentially faulting references?

	-hpa
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/