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

From: Christian KÃnig
Date: Fri Jun 08 2018 - 02:44:29 EST


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.