> -----Original Message----- > From: Daniel Vetter [mailto:daniel.vetter@xxxxxxxx] On Behalf Of Daniel > Vetter > Sent: Saturday, March 14, 2015 1:14 AM > To: Chris Wilson; Daniel Vetter; Weinehall, David; Zou, Nanhai; Song, Ruiling; > Vetter, Daniel; intel-gfx@xxxxxxxxxxxxxxxxxxxxx; Yang, Rong R; > beignet@xxxxxxxxxxxxxxxxxxxxx > Subject: Re: [Beignet] Preventing zero GPU virtual address > allocation > > On Fri, Mar 13, 2015 at 04:58:47PM +0000, Chris Wilson wrote: > > On Fri, Mar 13, 2015 at 10:27:38AM +0100, Daniel Vetter wrote: > > > If supporting systems without full ppgtt is a requirement for you > > > (still wonky on gen8 a bit, so might be a good strategy) then imo > > > it's the PIN_BIAS idea I've laid out earlier in this thread. That > > > one will work everywhere. softpin can unexpectedly fail without full > > > ppgtt if the kernel decides to put something at a given spot, which > > > imo means we should only expose it on full ppgtt systems. > > > > > > And PIN_BIAS should be fairly easy to wire up since the internal > > > logic is all there already. So "just" needs an execbuf flag, igt > > > test and appropriate userspace to set that new bit. > > > > It doesn't though. To provide the guarantee userspace is asking for > > (which is that address 0 goes to a special, preferrably inaccessible, > > page), you have to evict the first N pages in the GGTT. That is just > > as likely to fail with an execbuffer flag as it would with an execobject flag. > > Afaiui userspace only needs the guarantee that NULL is never a valid address. > Which means it's never a valid address for its own buffer objects. I don't > think it cares one bit what's actually there, it's not mandatory to fault > apparently. And faulting is what's not possible. Yes, This is what exactly what we need, that is make NULL as an invalid address. It's just like C language. But I have some more comment. The buffer object used in opencl may be allocated in libva/opengl and shared for opencl usage through some opencl extension. Afaiui, this would implicitly require libva/mesa also avoid zero-address buffer object allocation. Will libdrm re-bind such kind of shared buffer object to a new graphics virtual address? So that PIN_BIAS is also effective on the shared buffer, right? Thanks! Ruiling > I guess the standard is like normal C: If you access a NULL pointer, anything > can happen (including garbage on the frontbuffer), the only guarantee you > need to make is that NULL is never a valid address. At least if no one plays > tricks ;-) -Daniel > -- > Daniel Vetter > Software Engineer, Intel Corporation > +41 (0) 79 365 57 48 - http://blog.ffwll.ch _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
