linux-kernel - Re: powerpc/perf: hw breakpoints return ENOSPC

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 16 Aug 2012 16:15:02 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Michael Ellerman <michael@...erman.id.au>
Cc:	Michael Neuling <mikey@...ling.org>,
	Ingo Molnar <mingo@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	K Prasad <prasad@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org
Subject: Re: powerpc/perf: hw breakpoints return ENOSPC

On Fri, 2012-08-17 at 00:02 +1000, Michael Ellerman wrote:
> You do want to guarantee that the task will always be subject to the
> breakpoint, even if it moves cpus. So is there any way to guarantee that
> other than reserving a breakpoint slot on every cpu ahead of time? 

That's not how regular perf works.. regular perf can overload hw
resources at will and stuff is strictly per-cpu.

So the regular perf record has perf_event_attr::inherit enabled by
default, this will result in it creating a per-task-per-cpu event for
each cpu and this will succeed because there's no strict reservation to
avoid/detect starvation against perf_event_attr::pinned events.

For regular (!pinned) events, we'll RR the created events on the
available hardware resources.

HWBP does things completely different and reserves a slot over all CPUs
for everything, thus stuff completely falls apart.

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