linux-kernel - Re: [PATCH 14/22] spufs: use SPU master control to prevent wild SPU execution

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Message-Id: <1172729890.5852.40.camel@concordia.ozlabs.ibm.com>
Date:	Thu, 01 Mar 2007 15:18:10 +0900
From:	Michael Ellerman <michael@...erman.id.au>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	cbe-oss-dev@...abs.org, linuxppc-dev@...abs.org,
	Paul Mackerras <paulus@...ba.org>,
	linux-kernel@...r.kernel.org,
	Arnd Bergmann <arnd.bergmann@...ibm.com>,
	Jeremy Kerr <jk@...abs.org>
Subject: Re: [PATCH 14/22] spufs: use SPU master control to prevent wild
	SPU execution

On Mon, 2006-11-20 at 18:45 +0100, Arnd Bergmann wrote:
> plain text document attachment (spufs-master-control.diff)
> When the user changes the runcontrol register, an SPU might be
> running without a process being attached to it and waiting for
> events. In order to prevent this, make sure we always disable
> the priv1 master control when we're not inside of spu_run.

Hi Arnd,

Sorry I didn't comment on this when you sent it, I wasn't paying enough
attention. This patch confuses me, you say we should make sure we always
disable the master control when we're not inside spu_run, but I see
several exit paths where we leave the master run bit enabled - or maybe
I'm reading it wrong.

I think I've also seen it happen:

[root@...alhost dma5]# ./put-test 
10963.13
[root@...alhost dma5]# find /spu
/spu
[root@...alhost dma5]# echo x > /proc/sysrq-trigger 
SysRq : Entering xmon

0:mon> ss
..
Stopped spu 06, was running (mfc_sr1: 0x32 runcntl: 0x1)
Stopped spu 07, was running (mfc_sr1: 0x32 runcntl: 0x1)
..

cheers

-- 
Michael Ellerman
OzLabs, IBM Australia Development Lab

wwweb: http://michael.ellerman.id.au
phone: +61 2 6212 1183 (tie line 70 21183)

We do not inherit the earth from our ancestors,
we borrow it from our children. - S.M.A.R.T Person

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