Re: [PATCH 00/03] Preventing zero GPU virtual address allocation

Zou, Nanhai
2015-05-27T07:54:48Z

> -----Original Message-----
> From: Intel-gfx [mailto:intel-gfx-bounces@lists.freedesktop.org] On Behalf Of
> Daniel Vetter
> Sent: Thursday, May 21, 2015 12:01 AM
> To: Chris Wilson; intel-gfx
> Subject: Re: [Intel-gfx] [PATCH 00/03] Preventing zero GPU virtual address
> allocation
>
> On Wed, May 20, 2015 at 03:14:06PM +0100, Chris Wilson wrote:
> > On Wed, May 20, 2015 at 03:09:43PM +0100, Chris Wilson wrote:
> > > On Wed, May 20, 2015 at 04:54:19PM +0300, David Weinehall wrote:
> > > > This patch series (one patch each for libdrm, the kernel, and
> > > > beignet) aims to provide a means to add a context-specific means
> > > > to prevent a mapping to GPU virtual address zero. This is needed
> > > > at least by Beignet (possibly in other use-cases too, though I
> > > > don't know of any
> > > > other) to allow use of address zero to represent NULL.
> > >
> > > Urm, you cannot allow absolute addressing period. What happens to
> > > the object at 0 when the user reads from it or writes to it? You
> > > have to have an object at 0 for the user's NULL pointer access.
> >
> > I'll mollify that: outside of full-ppgtt where you need to share the VM.
>
> The description is misleading, the new flag doesn't prevent anything from
> getting mapped at 0 but only prevents any bo submitted through execbuf on
> the given context from being bound at address 0. If that would happen
> compute kernels using NULL checks for some things would fall over.
>
> Essentially it applies the PIN_BIAS for all execbuf objects, which works even on
> ggtt execbufs.
>
> Patches themselves look good, but we miss the igt to update the invalid ctx
> flags testcase. And a bare minimal function testcase (which checks the reloc
> offset with and without a ctx with this flag set) would be nice too.
> With that and an r-b from the beignet developers I'll pull this in.
> -Daniel

Hi,
We can verify the patches work for Beignet.

Thanks
Zou Nanhai

> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
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