Re: [PATCH v2] gpu: drm: ttm: Adding new return type vm_fault_t

[Christian KÃnig]

Am 08.06.2018 um 06:36 schrieb Souptick Joarder:
> On Sat, Jun 2, 2018 at 12:57 AM, Souptick Joarder <jrdr.linux@xxxxxxxxx> wrote:
> > Use new return type vm_fault_t for fault handler. For
> > now, this is just documenting that the function returns
> > a VM_FAULT value rather than an errno. Once all instances
> > are converted, vm_fault_t will become a distinct type.
> >
> > Ref-> commit 1c8f422059ae ("mm: change return type to vm_fault_t")
> >
> > Previously vm_insert_{mixed,pfn} returns err which driver
> > mapped into VM_FAULT_* type. The new function
> > vmf_insert_{mixed,pfn} will replace this inefficiency by
> > returning VM_FAULT_* type.
> >
> > Signed-off-by: Souptick Joarder <jrdr.linux@xxxxxxxxx>
> > ---
> > v2: Address christian's comment. Put reverse
> >      xmas tree order for variable declarations.
> >
> >   drivers/gpu/drm/ttm/ttm_bo_vm.c | 45 ++++++++++++++++++++---------------------
> >   1 file changed, 22 insertions(+), 23 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> > index 8eba95b..9de8b4f 100644
> > --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
> > +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> > @@ -43,10 +43,11 @@
> >
> >   #define TTM_BO_VM_NUM_PREFAULT 16
> >
> > -static int ttm_bo_vm_fault_idle(struct ttm_buffer_object *bo,
> > +static vm_fault_t ttm_bo_vm_fault_idle(struct ttm_buffer_object *bo,
> >                                  struct vm_fault *vmf)
> >   {
> > -       int ret = 0;
> > +       vm_fault_t ret = 0;
> > +       int err = 0;
> >
> >          if (likely(!bo->moving))
> >                  goto out_unlock;
> > @@ -77,9 +78,9 @@ static int ttm_bo_vm_fault_idle(struct ttm_buffer_object *bo,
> >          /*
> >           * Ordinary wait.
> >           */
> > -       ret = dma_fence_wait(bo->moving, true);
> > -       if (unlikely(ret != 0)) {
> > -               ret = (ret != -ERESTARTSYS) ? VM_FAULT_SIGBUS :
> > +       err = dma_fence_wait(bo->moving, true);
> > +       if (unlikely(err != 0)) {
> > +               ret = (err != -ERESTARTSYS) ? VM_FAULT_SIGBUS :
> >                          VM_FAULT_NOPAGE;
> >                  goto out_unlock;
> >          }
> > @@ -104,7 +105,7 @@ static unsigned long ttm_bo_io_mem_pfn(struct ttm_buffer_object *bo,
> >                  + page_offset;
> >   }
> >
> > -static int ttm_bo_vm_fault(struct vm_fault *vmf)
> > +static vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
> >   {
> >          struct vm_area_struct *vma = vmf->vma;
> >          struct ttm_buffer_object *bo = (struct ttm_buffer_object *)
> > @@ -115,8 +116,9 @@ static int ttm_bo_vm_fault(struct vm_fault *vmf)
> >          unsigned long pfn;
> >          struct ttm_tt *ttm = NULL;
> >          struct page *page;
> > -       int ret;
> > +       int err;
> >          int i;
> > +       vm_fault_t ret = VM_FAULT_NOPAGE;
> >          unsigned long address = vmf->address;
> >          struct ttm_mem_type_manager *man =
> >                  &bdev->man[bo->mem.mem_type];
> > @@ -128,9 +130,9 @@ static int ttm_bo_vm_fault(struct vm_fault *vmf)
> >           * for reserve, and if it fails, retry the fault after waiting
> >           * for the buffer to become unreserved.
> >           */
> > -       ret = ttm_bo_reserve(bo, true, true, NULL);
> > -       if (unlikely(ret != 0)) {
> > -               if (ret != -EBUSY)
> > +       err = ttm_bo_reserve(bo, true, true, NULL);
> > +       if (unlikely(err != 0)) {
> > +               if (err != -EBUSY)
> >                          return VM_FAULT_NOPAGE;
> >
> >                  if (vmf->flags & FAULT_FLAG_ALLOW_RETRY) {
> > @@ -162,8 +164,8 @@ static int ttm_bo_vm_fault(struct vm_fault *vmf)
> >          }
> >
> >          if (bdev->driver->fault_reserve_notify) {
> > -               ret = bdev->driver->fault_reserve_notify(bo);
> > -               switch (ret) {
> > +               err = bdev->driver->fault_reserve_notify(bo);
> > +               switch (err) {
> >                  case 0:
> >                          break;
> >                  case -EBUSY:
> > @@ -191,13 +193,13 @@ static int ttm_bo_vm_fault(struct vm_fault *vmf)
> >                  goto out_unlock;
> >          }
> >
> > -       ret = ttm_mem_io_lock(man, true);
> > -       if (unlikely(ret != 0)) {
> > +       err = ttm_mem_io_lock(man, true);
> > +       if (unlikely(err != 0)) {
> >                  ret = VM_FAULT_NOPAGE;
> >                  goto out_unlock;
> >          }
> > -       ret = ttm_mem_io_reserve_vm(bo);
> > -       if (unlikely(ret != 0)) {
> > +       err = ttm_mem_io_reserve_vm(bo);
> > +       if (unlikely(err != 0)) {
> >                  ret = VM_FAULT_SIGBUS;
> >                  goto out_io_unlock;
> >          }
> > @@ -265,23 +267,20 @@ static int ttm_bo_vm_fault(struct vm_fault *vmf)
> >                  }
> >
> >                  if (vma->vm_flags & VM_MIXEDMAP)
> > -                       ret = vm_insert_mixed(&cvma, address,
> > +                       ret = vmf_insert_mixed(&cvma, address,
> >                                          __pfn_to_pfn_t(pfn, PFN_DEV));
> >                  else
> > -                       ret = vm_insert_pfn(&cvma, address, pfn);
> > +                       ret = vmf_insert_pfn(&cvma, address, pfn);
> >
> >                  /*
> >                   * Somebody beat us to this PTE or prefaulting to
> >                   * an already populated PTE, or prefaulting error.
> >                   */
> >
> > -               if (unlikely((ret == -EBUSY) || (ret != 0 && i > 0)))
> > +               if (unlikely((ret == VM_FAULT_NOPAGE && i > 0)))
> >                          break;
> > -               else if (unlikely(ret != 0)) {
> > -                       ret =
> > -                           (ret == -ENOMEM) ? VM_FAULT_OOM : VM_FAULT_SIGBUS;
> > +               else if (unlikely(ret & VM_FAULT_ERROR))
> >                          goto out_io_unlock;
> > -               }
> >
> >                  address += PAGE_SIZE;
> >                  if (unlikely(++page_offset >= page_last))
> > --
> > 1.9.1
> If no further comment, we would like get this patch in 4.18 / 4.18-rc-x.
The patch looks good to me and I will pick it up for the next TTM pull 
request. I don't think it will make it into 4.18-rc-1, but 4.18-rc-x 
sounds realistic.

Christian.