linux-kernel - Re: [S390] minor fault path optimization.

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:	Mon, 19 Mar 2007 13:31:49 +0000
From:	Christoph Hellwig <hch@...radead.org>
To:	Martin Schwidefsky <schwidefsky@...ibm.com>
Cc:	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
	linux-arch@...r.kernel.org
Subject: Re: [S390] minor fault path optimization.

On Mon, Mar 19, 2007 at 02:02:06PM +0100, Martin Schwidefsky wrote:
> From: Martin Schwidefsky <schwidefsky@...ibm.com>
> 
> [S390] minor fault path optimization.
> 
> The minor fault path has grown a lot in terms of cycles. In particular
> the kprobes hook is very costly. Optimize the path to save a couple of
> cycles. If kprobes is enabled more than 300 cycles can be avoided if 
> kprobes_running() is false.

Actually there is a lot more fishy here.  This code is duplicated over
every single architecture.  It uses a notifier chain that only ever has
one actual uaesr.  It exports interfaces that are potential harmful.

Please do the right thing to optimize this instead and rip out the brandead
notifier chain mechanisms and directly call into the krobes handler if
kprobes are active, in particular the DIE_PAGE_FAULT: case of 
kprobe_exceptions_notify.  That allows you to optimize the path both
if kprobes are active, and even further if they're not.

The same should be done for all other architectures, and the other
(ab-)uses of  the kprobes notifiers.
-
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/