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Date: Fri, 16 Jul 2010 21:15:25 +0300
From: Avi Kivity <avi@redhat.com>
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To: "H. Peter Anvin" <hpa@zytor.com>
CC: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        LKML <linux-kernel@vger.kernel.org>,
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Subject: Re: [patch 2/2] x86 NMI-safe INT3 and Page Fault
References: <20100714154923.947138065@efficios.com> <20100714155804.252253097@efficios.com> <4C405078.20707@redhat.com> <20100716144927.GA22516@Krystal> <4C408D0C.5050709@redhat.com> <20100716165855.GA3836@Krystal> <4C409CBA.1050709@redhat.com> <4C409F62.6030303@zytor.com>
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On 07/16/2010 09:05 PM, H. Peter Anvin wrote:
>
>> Module loading can certainly take a vmalloc_sync_all() (though I agree
>> it's unpleasant).  Anything else?
>>
>> Note perf is not modular at this time, but could be made so with
>> preempt/sched notifiers to hook the context switch.
>>
>>      
> Actually, module loading is already a performance problem; a lot of
> distros load sometimes hundreds of modules on startup, and it's heavily
> serialized, so I can see this being desirable to skip.
>    

There aren't that many processes at this time (or there shouldn't be, 
don't know how fork-happy udev is at this stage), so the sync should be 
pretty fast.  In any case, we can sync only modules that contain NMI 
handlers.

> I really hope noone ever gets the idea of touching user space from an
> NMI handler, though, and expecting it to work...
>    

I think the concern here is about an NMI handler's code running in 
vmalloc space, or is it something else?

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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