Re: [PATCH] drm/radeon: fix VM page table setup on SI

["Michel Dänzer" <michel@daenzer.net>]

On Fre, 2012-06-29 at 11:28 -0400, Jerome Glisse wrote: 
> On Fri, Jun 29, 2012 at 11:23 AM, Alex Deucher <alexdeucher@gmail.com> wrote:
> > On Fri, Jun 29, 2012 at 10:49 AM, Michel Dänzer <michel@daenzer.net> wrote:
> >> On Don, 2012-06-28 at 17:53 -0400, alexdeucher@gmail.com wrote:
> >>> From: Alex Deucher <alexander.deucher@amd.com>
> >>>
> >>> Cayman and trinity allow for variable sized VM page
> >>> tables, but SI requires that all page tables be the
> >>> same size.  The current code assumes variablely sized
> >>> VM page tables so SI may end up with part of each page
> >>> table overlapping with other memory which could end
> >>> up being interpreted by the VM hw as garbage.
> >>>
> >>> Change the code to better accomodate SI.  Allocate enough
> >>> space for at least 2 full page tables and always set
> >>> last_pfn to max_pfn on SI so each VM is backed by a full
> >>> page table.  This limits us to only 2 VMs active at any
> >>> given time on SI.  This will be rectified and the code can
> >>> be reunified once we move to two level page tables.
> >>>
> >>> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
> >>
> >> This change breaks the radeonsi driver for me. egltri_screen (the
> >> 'golden' test for radeonsi at least basically working) locks up the
> >> GPU.
> >>
> >> I don't have any details about the lockup yet, as the GPU reset attempt
> >> hangs the machine. Any ideas offhand what radeonsi might be doing wrong?
> >
> > Maybe trying to access an unmapped page that happened to work by
> > accident before and now causes a fault in the VM which halts the MC?

Indeed, looks like it:

radeon 0000:01:00.0:   VM_CONTEXT1_PROTECTION_FAULT_ADDR   0x000FF01B
radeon 0000:01:00.0:   VM_CONTEXT1_PROTECTION_FAULT_STATUS 0x0202400C

Oddly, while I have seen similar errors before (so at 
least some access to unmapped pages was caught even before your patch),
I hadn't noticed them for a while with egltri_screen...


Anyway, some more experimentation shows that it doesn't happen if I skip
the clear, and it still happens when doing only a clear. I'll look into
what might be wrong with the clears next week.


> Yeah only thing i can think of, can you get dump of various mc fault
> reg after lockup ?

Did you have any particular registers in mind?


-- 
Earthling Michel Dänzer           |                   http://www.amd.com
Libre software enthusiast         |          Debian, X and DRI developer