[PATCH] drm/i915/gvt: set shadow entry to scratch page when guest driver only update partial of the GGTT entry

[Xiaoguang Chen]

Sometimes guest driver only update partial of GGTT entry then
access it. In this situation the gfn we got from the GGTT table
is invalid and can not be translate to a valid mfn.
p2m translation should happen only when the whole parts of a
GGTT entry got updated.

Setting the shadow entry pointing to a scratch page instead if only
partial of GGTT entry updated.

Signed-off-by: Zhi Wang <zhi.a.wang at intel.com>
SIgned-off-by: Xiaoguang Chen <xiaoguang.chen at intel.com>
---
 drivers/gpu/drm/i915/gvt/gtt.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/gvt/gtt.c b/drivers/gpu/drm/i915/gvt/gtt.c
index da73127..119cd30 100644
--- a/drivers/gpu/drm/i915/gvt/gtt.c
+++ b/drivers/gpu/drm/i915/gvt/gtt.c
@@ -1837,11 +1837,21 @@ static int emulate_gtt_mmio_write(struct intel_vgpu *vgpu, unsigned int off,
 		ret = gtt_entry_p2m(vgpu, &e, &m);
 		if (ret) {
 			gvt_vgpu_err("fail to translate guest gtt entry\n");
-			return ret;
+			/* guest driver may read/write the entry when only
+			 * partial of the guest entry got updated.
+			 * In this situation the gfn we got from GGTT table is
+			 * invalid and can not be translated to a valid mfn.
+			 * p2m translation should happen only after the whole
+			 * parts of a GGTT entry got updated.
+			 *
+			 * Setting the shadow entry pointing to a scratch page
+			 * instead while GGTT entry only got partial update.
+			 */
+			ops->set_pfn(&m, gvt->gtt.scratch_ggtt_mfn);
 		}
 	} else {
 		m = e;
-		m.val64 = 0;
+		ops->set_pfn(&m, gvt->gtt.scratch_ggtt_mfn);
 	}
 
 	ggtt_set_shadow_entry(ggtt_mm, &m, g_gtt_index);
-- 
2.7.4