From: Chris Wilson <chris@chris-wilson.co.uk>
To: Keith Packard <keithp@keithp.com>, intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH 2/2] drm/i915: Disable page-faults around the fast pwrite/pread paths
Date: Sat, 09 Jul 2011 21:50:26 +0100 [thread overview]
Message-ID: <aefc95$ohq3u@orsmga001.jf.intel.com> (raw)
In-Reply-To: <yunvcvbfbj1.fsf@aiko.keithp.com>
On Sat, 09 Jul 2011 13:24:02 -0700, Keith Packard <keithp@keithp.com> wrote:
> On Sat, 9 Jul 2011 09:38:51 +0100, Chris Wilson <chris@chris-wilson.co.uk> wrote:
>
> > + /* We have to disable faulting here in case the user address
> > + * is really a GTT mapping and so we can not enter
> > + * i915_gem_fault() whilst already holding struct_mutex.
> > + */
>
> I would (far, far) rather disallow pread through the GTT
> mapping. There's no credible reason to allow it. Is there some
> reasonably fast way to detect that these addresses are within the GTT
> and just bail?
Something like:
vma = find_vma(current->mm, uaddr);
if (vma->vm_ops == dev->driver->gem_vm_ops)
return -EINVAL;
I think would do, find_vma() is not necessary cheap though, and there are a
couple of optimisations that we haven't done for pwrite/pread yet to speed
up the transition to the slow path.
> Any performance penalty that serves solely to enable abuse of the
> interface is not reasonable.
The current code generates lockdep OOPSes and inconsistently applies
pagefault_disable along some paths, in particular for 32-bit kernels,
but not others. And the abuse is permitted through the OpenGL
specification, I believe. The offending app is just doing
glBufferData(glMapBuffer()), iiuc;
-Chris
--
Chris Wilson, Intel Open Source Technology Centre
next prev parent reply other threads:[~2011-07-09 20:50 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-07-09 8:38 [PATCH 1/2] drm/i915: Prefault all pages for pread and pwrite Chris Wilson
2011-07-09 8:38 ` [PATCH 2/2] drm/i915: Disable page-faults around the fast pwrite/pread paths Chris Wilson
2011-07-09 14:41 ` Eric Anholt
2011-07-09 17:40 ` Chris Wilson
2011-07-09 20:24 ` Keith Packard
2011-07-09 20:50 ` Chris Wilson [this message]
2011-07-09 21:06 ` Keith Packard
2011-07-09 21:23 ` Chris Wilson
2011-07-09 22:07 ` Keith Packard
2011-07-11 16:51 ` Chris Wilson
2011-07-11 19:55 ` Keith Packard
2011-07-10 18:45 ` Eric Anholt
2011-07-10 20:29 ` Keith Packard
2011-07-09 20:21 ` [PATCH 1/2] drm/i915: Prefault all pages for pread and pwrite Keith Packard
2011-07-09 20:31 ` Chris Wilson
2011-07-10 1:40 ` Ben Widawsky
2011-07-10 8:08 ` Chris Wilson
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