Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain support to use NMI-safe methods
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- Subject: Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain support to use NMI-safe methods
- From: "H. Peter Anvin" <hpa@xxxxxxxxx>
- Date: Mon, 15 Jun 2009 11:38:00 -0700
- Cc: Ingo Molnar <mingo@xxxxxxx>, mingo@xxxxxxxxxx, mathieu.desnoyers@xxxxxxxxxx, paulus@xxxxxxxxx, acme@xxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, a.p.zijlstra@xxxxxxxxx, penberg@xxxxxxxxxxxxxx, vegard.nossum@xxxxxxxxx, efault@xxxxxx, jeremy@xxxxxxxx, npiggin@xxxxxxx, tglx@xxxxxxxxxxxxx, linux-tip-commits@xxxxxxxxxxxxxxx
- In-reply-to: <alpine.LFD.2.01.0906151029160.3305@xxxxxxxxxxxxxxxxxxxxx>
- References: <tip-74193ef0ecab92535c8517f082f1f50504526c9b@xxxxxxxxxxxxxx> <alpine.LFD.2.01.0906151007560.3305@xxxxxxxxxxxxxxxxxxxxx> <20090615171845.GA7664@xxxxxxx> <alpine.LFD.2.01.0906151029160.3305@xxxxxxxxxxxxxxxxxxxxx>
- User-agent: Thunderbird 2.0.0.21 (X11/20090320)
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
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