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

["Christian König" <christian.koenig@amd.com>]

Am 08.06.2018 um 06:36 schrieb Souptick Joarder:
> On Sat, Jun 2, 2018 at 12:57 AM, Souptick Joarder <jrdr.linux@gmail.com> 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@gmail.com>
>> ---
>> 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.