drm/vmwgfx: Check pin count before attempting to move a buffer

In certain scenarios, e.g. when fbdev is enabled, we can get into
a situation where a vmw_framebuffer_pin() is called on a buffer
that is already pinned.

When this happens, ttm_bo_validate() will unintentially remove the
TTM_PL_FLAG_NO_EVICT flag, thus unpinning it, and leaving no way
to actually pin the buffer again.

To prevent this, if a buffer is already pinned, then instead of
calling ttm_bo_validate(), just make sure the proposed placement is
compatible with the existing placement.
Signed-off-by: Sinclair Yeh <syeh@vmware.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>
Cc: <stable@vger.kernel.org>
---
This is the 2nd patch in a 3-patch series to fix a console black
screen issue on Ubuntu 16.04 server.  This fixes a BUG_ON()
condition where a pinned buffer gets accidentally put onto the
LRU list.

drivers/gpu/drm/vmwgfx/vmwgfx_dmabuf.c

@@ -49,6 +49,7 @@ int vmw_dmabuf_pin_in_placement(struct vmw_private *dev_priv,
 {
 	struct ttm_buffer_object *bo = &buf->base;
 	int ret;
+	uint32_t new_flags;
 
 	ret = ttm_write_lock(&dev_priv->reservation_sem, interruptible);
 	if (unlikely(ret != 0))
@@ -60,7 +61,12 @@ int vmw_dmabuf_pin_in_placement(struct vmw_private *dev_priv,
 	if (unlikely(ret != 0))
 		goto err;
 
+	if (buf->pin_count > 0)
+		ret = ttm_bo_mem_compat(placement, &bo->mem,
+					&new_flags) == true ? 0 : -EINVAL;
+	else
 		ret = ttm_bo_validate(bo, placement, interruptible, false);
+
 	if (!ret)
 		vmw_bo_pin_reserved(buf, true);
 
@@ -91,6 +97,7 @@ int vmw_dmabuf_pin_in_vram_or_gmr(struct vmw_private *dev_priv,
 {
 	struct ttm_buffer_object *bo = &buf->base;
 	int ret;
+	uint32_t new_flags;
 
 	ret = ttm_write_lock(&dev_priv->reservation_sem, interruptible);
 	if (unlikely(ret != 0))
@@ -102,6 +109,12 @@ int vmw_dmabuf_pin_in_vram_or_gmr(struct vmw_private *dev_priv,
 	if (unlikely(ret != 0))
 		goto err;
 
+	if (buf->pin_count > 0) {
+		ret = ttm_bo_mem_compat(&vmw_vram_gmr_placement, &bo->mem,
+					&new_flags) == true ? 0 : -EINVAL;
+		goto out_unreserve;
+	}
+
 	ret = ttm_bo_validate(bo, &vmw_vram_gmr_placement, interruptible,
 			      false);
 	if (likely(ret == 0) || ret == -ERESTARTSYS)
@@ -161,6 +174,7 @@ int vmw_dmabuf_pin_in_start_of_vram(struct vmw_private *dev_priv,
 	struct ttm_placement placement;
 	struct ttm_place place;
 	int ret = 0;
+	uint32_t new_flags;
 
 	place = vmw_vram_placement.placement[0];
 	place.lpfn = bo->num_pages;
@@ -185,9 +199,14 @@ int vmw_dmabuf_pin_in_start_of_vram(struct vmw_private *dev_priv,
 	 */
 	if (bo->mem.mem_type == TTM_PL_VRAM &&
 	    bo->mem.start < bo->num_pages &&
-	    bo->mem.start > 0)
+	    bo->mem.start > 0 &&
+	    buf->pin_count == 0)
 		(void) ttm_bo_validate(bo, &vmw_sys_placement, false, false);
 
+	if (buf->pin_count > 0)
+		ret = ttm_bo_mem_compat(&placement, &bo->mem,
+					&new_flags) == true ? 0 : -EINVAL;
+	else
 		ret = ttm_bo_validate(bo, &placement, interruptible, false);
 
 	/* For some reason we didn't end up at the start of vram */