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

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Date:	Wed, 07 Mar 2007 09:58:25 +0100
From:	Michael Ellerman <michael@...erman.id.au>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	cbe-oss-dev@...abs.org, linuxppc-dev@...abs.org,
	linux-kernel@...r.kernel.org
Subject: Re: [Cbe-oss-dev] [PATCH 14/22] spufs: use SPU master control
	to	prevent wild	SPU execution

On Mon, 2007-03-05 at 02:02 +0100, Arnd Bergmann wrote:
> On Friday 02 March 2007, Michael Ellerman wrote:
> > There's also the error case for spu_run_init() which skips the master
> > stop. I guess that's ok because we've only set the master control in the
> > backing store, and the only way that will ever get propagated to an
> > actual spu is by coming back thorough spufs_run_spu().
> 
> Hmm, the correct way would be to switch off the master control in there,
> afaics. Fixing it only in spu_run_init would mean that we also handle
> the case of spu_reacquire_runnable along with it.
> 
> > What originally caught my eye on this was the output from xmon. When we
> > drop into xmon with no spu programs running and stop the spus, it
> > reports that they _all_ have the master run enabled,
> 
> That looks right, there is no problem to have master control enabled,
> as long as user space can't access the spu through a context that is
> bound to it.
> 
> > and some of them 
> > have the runcntl enabled (those that have had spu programs run on them
> > since boot it seems).
> 
> While this sounds wrong. Maybe the runcntl is active on those that have
> _not_ run since boot, which would make more sense. We should investigate
> this.

No I'm pretty sure it's enabled on the ones that _have_ run since boot.
I'm booting up fresh, running two spu programs, and then I see two spus
with master and runcntl set.

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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