On 2015-11-06 02:28, Christian König wrote: > On 05.11.2015 20:06, Jay Cornwall wrote: >> The VM default page (used when a VM translation fails) is allocated in >> system memory. The VM is misconfigured to interpret the physical >> address >> as referencing a VRAM physical page. >> >> Route default page accesses to system memory. >> >> Signed-off-by: Jay Cornwall <jay at jcornwall.me> >> Cc: <stable at vger.kernel.org> # v4.2+ > > Nice catch, patch is Reviewed-by: Christian König > <christian.koenig at amd.com> > > Do we also need this for Radeon?
It looks like this field was introduced in CIK. This change could be replicated in radeon on those parts, but I haven't got one to test with. I'm not sure if this misconfiguration is fatal. The default page should be used for loads only. I haven't been able to get anything besides 0 from a faulting load on my Fiji with a system or VRAM default page. A physical address > VRAM doesn't seem to cause problems, either. My primary motivation for this change is to allow HSA to handle faulting atomic operations. The KFD exposes a MTYPE=UC aperture to the user which allows atomics to be forwarded to system memory, via MC/BIF/PCI. When one of these atomic operations faults the MC is unable to handle the VRAM atomic (atomics are implemented by TC) and the TC hangs waiting for a response. If the default page is directed towards BIF then the atomic is correctly discarded. -- Jay Cornwall
