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 13:42:32 -0700
- Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Ingo Molnar <mingo@xxxxxxx>, Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>, mingo@xxxxxxxxxx, paulus@xxxxxxxxx, acme@xxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, a.p.zijlstra@xxxxxxxxx, penberg@xxxxxxxxxxxxxx, vegard.nossum@xxxxxxxxx, efault@xxxxxx, npiggin@xxxxxxx, tglx@xxxxxxxxxxxxx, linux-tip-commits@xxxxxxxxxxxxxxx
- In-reply-to: <alpine.LFD.2.01.0906151326170.6276@xxxxxxxxxxxxxxxxxxxxx>
- References: <tip-74193ef0ecab92535c8517f082f1f50504526c9b@xxxxxxxxxxxxxx> <alpine.LFD.2.01.0906151007560.3305@xxxxxxxxxxxxxxxxxxxxx> <20090615171845.GA7664@xxxxxxx> <alpine.LFD.2.01.0906151029160.3305@xxxxxxxxxxxxxxxxxxxxx> <20090615180527.GB4201@Krystal> <alpine.LFD.2.01.0906151125320.6276@xxxxxxxxxxxxxxxxxxxxx> <20090615183649.GA16999@xxxxxxx> <alpine.LFD.2.01.0906151152170.6276@xxxxxxxxxxxxxxxxxxxxx> <4A36ABB5.1040109@xxxxxxxx> <alpine.LFD.2.01.0906151326170.6276@xxxxxxxxxxxxxxxxxxxxx>
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Linus Torvalds wrote:
>
> On Mon, 15 Jun 2009, Jeremy Fitzhardinge wrote:
>> We have to restore the usermode %gs somewhere...
>
> None of this is useful for user-mode return _anyway_, since you have to
> restore %cs/%ss too. At that point, you have to use iret.
>
cs/ss you could potentially restore with sysret/sysexit, at least for
the common case. Of course, this means more cases...
-hpa
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