Re: [PATCH v3 4/6] drm/xe: Use ttm_bo_access in xe_vm_snapshot_capture_delayed

[Matthew Brost <matthew.brost@intel.com>]

On Mon, Oct 21, 2024 at 10:07:31AM +0100, Matthew Auld wrote:
> On 19/10/2024 20:20, Matthew Brost wrote:
> > Non-contiguous mapping of BO in VRAM doesn't work, use ttm_bo_access
> > instead.
> > 
> > v2:
> >   - Fix error handling
> > 
> > Fixes: 0eb2a18a8fad ("drm/xe: Implement VM snapshot support for BO's and userptr")
> > Suggested-by: Matthew Auld <matthew.auld@intel.com>
> > Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> 
> The other user looks to be the clear color stuff for display. See
> intel_bo_read_from_page(). I think that is also potentially busted?
> 

I looked at display but missed this. Will fix in next rev.

> > ---
> >   drivers/gpu/drm/xe/xe_vm.c | 17 ++++++-----------
> >   1 file changed, 6 insertions(+), 11 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
> > index c99380271de6..c8782da3a5c3 100644
> > --- a/drivers/gpu/drm/xe/xe_vm.c
> > +++ b/drivers/gpu/drm/xe/xe_vm.c
> > @@ -3303,7 +3303,6 @@ void xe_vm_snapshot_capture_delayed(struct xe_vm_snapshot *snap)
> >   	for (int i = 0; i < snap->num_snaps; i++) {
> >   		struct xe_bo *bo = snap->snap[i].bo;
> > -		struct iosys_map src;
> >   		int err;
> >   		if (IS_ERR(snap->snap[i].data))
> > @@ -3316,16 +3315,12 @@ void xe_vm_snapshot_capture_delayed(struct xe_vm_snapshot *snap)
> >   		}
> >   		if (bo) {
> > -			xe_bo_lock(bo, false);
> 
> I think we still need the lock, or is that grabbed somewhere else? Also I
> guess CI doesn't currently hit this path?
> 

Yep. ttm_bo_access does a ttm_bo_reserve / ttm_bo_unreserve which is a
lock / unlock.

Matt

> > -			err = ttm_bo_vmap(&bo->ttm, &src);
> > -			if (!err) {
> > -				xe_map_memcpy_from(xe_bo_device(bo),
> > -						   snap->snap[i].data,
> > -						   &src, snap->snap[i].bo_ofs,
> > -						   snap->snap[i].len);
> > -				ttm_bo_vunmap(&bo->ttm, &src);
> > -			}
> > -			xe_bo_unlock(bo);
> > +			err = ttm_bo_access(&bo->ttm, snap->snap[i].bo_ofs,
> > +					    snap->snap[i].data, snap->snap[i].len, 0);
> > +			if (!(err < 0) && err != snap->snap[i].len)
> > +				err = -EIO;
> > +			else if (!(err < 0))
> > +				err = 0;
> >   		} else {
> >   			void __user *userptr = (void __user *)(size_t)snap->snap[i].bo_ofs;