[PATCH] drm/vmwgfx: Don't use screen objects when SEV is active

[Zack Rusin]

From: Zack Rusin <zackr at vmware.com>

When SEV is enabled gmr's and mob's are explicitly disabled because
the encrypted system memory can not be used by the hypervisor.

The driver was disabling GMR's but the presentation code, which depends
on GMR's, wasn't honoring it which lead to black screen on hosts
with SEV enabled.

Make sure screen objects presentation is not used when guest memory
regions have been disabled to fix presentation on SEV enabled hosts.

Fixes: 3b0d6458c705 ("drm/vmwgfx: Refuse DMA operation when SEV encryption is active")
Cc: <stable at vger.kernel.org> # v5.7+
Signed-off-by: Zack Rusin <zackr at vmware.com>
Reported-by: Nicholas Hunt <nhunt at vmware.com>
---
 drivers/gpu/drm/vmwgfx/vmwgfx_scrn.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_scrn.c b/drivers/gpu/drm/vmwgfx/vmwgfx_scrn.c
index 8db61c541a80..e1f36a09c59c 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_scrn.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_scrn.c
@@ -926,6 +926,10 @@ int vmw_kms_sou_init_display(struct vmw_private *dev_priv)
 	struct drm_device *dev = &dev_priv->drm;
 	int i;
 
+	/* Screen objects won't work if GMR's aren't available */
+	if (!dev_priv->has_gmr)
+		return -ENOSYS;
+
 	if (!(dev_priv->capabilities & SVGA_CAP_SCREEN_OBJECT_2)) {
 		return -ENOSYS;
 	}
-- 
2.37.2