drm/vmwgfx: Enable DMA mappings with SEV

Enable DMA mappings in vmwgfx after TTM has been fixed in commit
3bf3710 ("drm/ttm: Add a generic TTM memcpy move for page-based iomem")

This enables full guest-backed memory support and in particular allows
usage of screen targets as the presentation mechanism.

Signed-off-by: Zack Rusin <[email protected]>
Reported-by: Ye Li <[email protected]>
Tested-by: Ye Li <[email protected]>
Fixes: 3b0d645 ("drm/vmwgfx: Refuse DMA operation when SEV encryption is active")
Cc: Broadcom internal kernel review list <[email protected]>
Cc: [email protected]
Cc: <[email protected]> # v6.6+
Reviewed-by: Martin Krastev <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

Author: zackr

drivers/gpu/drm/vmwgfx/vmwgfx_drv.c

@@ -666,11 +666,12 @@ static int vmw_dma_select_mode(struct vmw_private *dev_priv)
 		[vmw_dma_map_populate] = "Caching DMA mappings.",
 		[vmw_dma_map_bind] = "Giving up DMA mappings early."};
 
-	/* TTM currently doesn't fully support SEV encryption. */
-	if (cc_platform_has(CC_ATTR_MEM_ENCRYPT))
-		return -EINVAL;
-
-	if (vmw_force_coherent)
+	/*
+	 * When running with SEV we always want dma mappings, because
+	 * otherwise ttm tt pool pages will bounce through swiotlb running
+	 * out of available space.
+	 */
+	if (vmw_force_coherent || cc_platform_has(CC_ATTR_MEM_ENCRYPT))
 		dev_priv->map_mode = vmw_dma_alloc_coherent;
 	else if (vmw_restrict_iommu)
 		dev_priv->map_mode = vmw_dma_map_bind;