drm/vmwgfx: Refuse DMA operation when SEV encryption is active

TTM doesn't yet fully support mapping of DMA memory when SEV is active,
so in that case, refuse DMA operation. For guest-backed object operation
this means 3D acceleration will be disabled. For host-backed, VRAM will be
used for data transfer between the guest and the device.
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Brian Paul <brianp@vmware.com>

drivers/gpu/drm/vmwgfx/vmwgfx_drv.c

@@ -29,6 +29,7 @@
 #include <linux/dma-mapping.h>
 #include <linux/module.h>
 #include <linux/pci.h>
+#include <linux/mem_encrypt.h>
 
 #include <drm/drm_drv.h>
 #include <drm/drm_ioctl.h>
@@ -575,6 +576,10 @@ 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 (mem_encrypt_active())
+		return -EINVAL;
+
 	if (vmw_force_coherent)
 		dev_priv->map_mode = vmw_dma_alloc_coherent;
 	else if (vmw_restrict_iommu)