Re: [Intel-gfx] [PATCH v3 06/12] drm/ttm: add TTM_PAGE_FLAG_EXTERNAL_MAPPABLE

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

On Thu, 2021-09-16 at 08:55 +0200, Christian König wrote:
> 
> 
> Am 15.09.21 um 20:59 schrieb Matthew Auld:
> > In commit:
> > 
> > commit 667a50db0477d47fdff01c666f5ee1ce26b5264c
> > Author: Thomas Hellstrom <thellstrom@vmware.com>
> > Date:   Fri Jan 3 11:17:18 2014 +0100
> > 
> >      drm/ttm: Refuse to fault (prime-) imported pages
> > 
> > we introduced the restriction that imported pages should not be
> > directly
> > mappable through TTM(this also extends to userptr). In the next
> > patch we
> > want to introduce a shmem_tt backend, which should follow all the
> > existing rules with TTM_PAGE_FLAG_EXTERNAL, since it will need to
> > handle
> > swapping itself, but with the above mapping restriction lifted.
> > 
> > Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> > Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> > Cc: Christian König <christian.koenig@amd.com>
> > ---
> >   drivers/gpu/drm/ttm/ttm_bo_vm.c | 6 ++++--
> >   include/drm/ttm/ttm_tt.h        | 7 +++++++
> >   2 files changed, 11 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c
> > b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> > index 708390588c7c..fd6e18f12f50 100644
> > --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
> > +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> > @@ -163,8 +163,10 @@ vm_fault_t ttm_bo_vm_reserve(struct
> > ttm_buffer_object *bo,
> >          * (if at all) by redirecting mmap to the exporter.
> >          */
> >         if (bo->ttm && (bo->ttm->page_flags &
> > TTM_PAGE_FLAG_EXTERNAL)) {
> > -               dma_resv_unlock(bo->base.resv);
> > -               return VM_FAULT_SIGBUS;
> > +               if (!(bo->ttm->page_flags &
> > TTM_PAGE_FLAG_EXTERNAL_MAPPABLE)) {

I saw there was previously a thought about testing for ttm_bo_type_sg
here. Was that a dead end?

Thanks,
Thomas