drm/ttm: Allow vm fault retries

Make use of the FAULT_FLAG_ALLOW_RETRY flag to allow dropping the
mmap_sem while waiting for bo idle.

FAULT_FLAG_ALLOW_RETRY appears to be primarily designed for disk waits
but should work just as fine for GPU waits..

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Jakob Bornecrantz <jakob@vmware.com>

1 files changed, 50 insertions, 12 deletions

diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
index 1006c15445e9..c03514b93f9c 100644
--- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
@@ -41,6 +41,51 @@
 
 #define TTM_BO_VM_NUM_PREFAULT 16
 
+static int ttm_bo_vm_fault_idle(struct ttm_buffer_object *bo,
+                                struct vm_area_struct *vma,
+                                struct vm_fault *vmf)
+{
+        struct ttm_bo_device *bdev = bo->bdev;
+        int ret = 0;
+
+        spin_lock(&bdev->fence_lock);
+        if (likely(!test_bit(TTM_BO_PRIV_FLAG_MOVING, &bo->priv_flags)))
+                goto out_unlock;
+
+        /*
+         * Quick non-stalling check for idle.
+         */
+        ret = ttm_bo_wait(bo, false, false, true);
+        if (likely(ret == 0))
+                goto out_unlock;
+
+        /*
+         * If possible, avoid waiting for GPU with mmap_sem
+         * held.
+         */
+        if (vmf->flags & FAULT_FLAG_ALLOW_RETRY) {
+                ret = VM_FAULT_RETRY;
+                if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
+                        goto out_unlock;
+
+                up_read(&vma->vm_mm->mmap_sem);
+                (void) ttm_bo_wait(bo, false, true, false);
+                goto out_unlock;
+        }
+
+        /*
+         * Ordinary wait.
+         */
+        ret = ttm_bo_wait(bo, false, true, false);
+        if (unlikely(ret != 0))
+                ret = (ret != -ERESTARTSYS) ? VM_FAULT_SIGBUS :
+                        VM_FAULT_NOPAGE;
+
+out_unlock:
+        spin_unlock(&bdev->fence_lock);
+        return ret;
+}
+
 static int ttm_bo_vm_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
         struct ttm_buffer_object *bo = (struct ttm_buffer_object *)
@@ -91,18 +136,11 @@ static int ttm_bo_vm_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
          * Wait for buffer data in transit, due to a pipelined
          * move.
          */
-
-        spin_lock(&bdev->fence_lock);
-        if (test_bit(TTM_BO_PRIV_FLAG_MOVING, &bo->priv_flags)) {
-                ret = ttm_bo_wait(bo, false, true, false);
-                spin_unlock(&bdev->fence_lock);
-                if (unlikely(ret != 0)) {
-                        retval = (ret != -ERESTARTSYS) ?
-                            VM_FAULT_SIGBUS : VM_FAULT_NOPAGE;
-                        goto out_unlock;
-                }
-        } else
-                spin_unlock(&bdev->fence_lock);
+        ret = ttm_bo_vm_fault_idle(bo, vma, vmf);
+        if (unlikely(ret != 0)) {
+                retval = ret;
+                goto out_unlock;
+        }
 
         ret = ttm_mem_io_lock(man, true);
         if (unlikely(ret != 0)) {