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From: Peter Zijlstra <peterz@infradead.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
	Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH] perf/ring_buffer: ensure atomicity and order of updates
Date: Mon, 14 May 2018 17:24:28 +0200	[thread overview]
Message-ID: <20180514152428.GS12217@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20180514152022.z3hnkkj3rbcabtyy@lakrids.cambridge.arm.com>

On Mon, May 14, 2018 at 04:20:23PM +0100, Mark Rutland wrote:

> > @@ -10499,6 +10523,9 @@ SYSCALL_DEFINE5(perf_event_open,
> >  		goto err_cred;
> >  	}
> >  
> > +	if (in_compat_syscall())
> > +		event->event_caps |= PERF_EV_CAP_COMPAT;
> > +
> 
> After a native perf_event_open, you could pass the fd (or exec) to
> another task that was compat (or vice-versa), so this wouldn't work in
> that case (crazy as it may be).
> 
> I don't have a better suggestion at present, though.

As discussed on IRC, we could trigger off of the buffer size; if the
buffer is <4G the &= UINT_MAX is harmless, if the buffer is larger, you
have to be using a 64bit thingy anyway.

Flipping the overflow functions around on attach/detach to buffers is a
little more dodgy, but could be done I suppose.

  reply	other threads:[~2018-05-14 15:24 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-10 13:06 [PATCH] perf/ring_buffer: ensure atomicity and order of updates Mark Rutland
2018-05-11  1:19 ` kbuild test robot
2018-05-11  1:19 ` kbuild test robot
2018-05-11 10:59 ` Mark Rutland
2018-05-11 16:22   ` Peter Zijlstra
2018-05-14 11:05     ` Mark Rutland
2018-05-14 11:28       ` Peter Zijlstra
2018-05-14 15:02         ` Peter Zijlstra
2018-05-14 15:20           ` Mark Rutland
2018-05-14 15:24             ` Peter Zijlstra [this message]
2018-05-23 16:42 ` Will Deacon

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