On Sat, 09 Jul 2011 13:24:02 -0700, Keith Packard <kei...@keithp.com> wrote:
> On Sat, 9 Jul 2011 09:38:51 +0100, Chris Wilson <ch...@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
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