[Intel-gfx] [PATCH v1 1/4] drm/i915/gvt: reorder the shadow ppgtt update process by adding entry first

[Tina Zhang]

Guest i915 driver may update the ppgtt table just before this workload
is going to be submitted to the hardware by device model. This case
wasn't handled well by device model before, due to the small time
window between removing old ppgtt entry and adding the new one. Errors
occur when the workload is executed by hardware during that small time
window. This patch is to remove this time window by adding the new ppgtt
entry first and then remove the old one.

Signed-off-by: Tina Zhang <tina.zhang at intel.com>
---
 drivers/gpu/drm/i915/gvt/gtt.c | 45 ++++++++++++++++++++++++++----------------
 1 file changed, 28 insertions(+), 17 deletions(-)

diff --git a/drivers/gpu/drm/i915/gvt/gtt.c b/drivers/gpu/drm/i915/gvt/gtt.c
index c6f0077..8caad86 100644
--- a/drivers/gpu/drm/i915/gvt/gtt.c
+++ b/drivers/gpu/drm/i915/gvt/gtt.c
@@ -975,29 +975,26 @@ static int ppgtt_populate_shadow_page(struct intel_vgpu_ppgtt_spt *spt)
 }
 
 static int ppgtt_handle_guest_entry_removal(struct intel_vgpu_guest_page *gpt,
-		unsigned long index)
+		struct intel_gvt_gtt_entry *se, unsigned long index)
 {
 	struct intel_vgpu_ppgtt_spt *spt = guest_page_to_ppgtt_spt(gpt);
 	struct intel_vgpu_shadow_page *sp = &spt->shadow_page;
 	struct intel_vgpu *vgpu = spt->vgpu;
 	struct intel_gvt_gtt_pte_ops *ops = vgpu->gvt->gtt.pte_ops;
-	struct intel_gvt_gtt_entry e;
 	int ret;
 
-	ppgtt_get_shadow_entry(spt, &e, index);
-
-	trace_gpt_change(spt->vgpu->id, "remove", spt, sp->type, e.val64,
+	trace_gpt_change(spt->vgpu->id, "remove", spt, sp->type, se->val64,
 			 index);
 
-	if (!ops->test_present(&e))
+	if (!ops->test_present(se))
 		return 0;
 
-	if (ops->get_pfn(&e) == vgpu->gtt.scratch_pt[sp->type].page_mfn)
+	if (ops->get_pfn(se) == vgpu->gtt.scratch_pt[sp->type].page_mfn)
 		return 0;
 
-	if (gtt_type_is_pt(get_next_pt_type(e.type))) {
+	if (gtt_type_is_pt(get_next_pt_type(se->type))) {
 		struct intel_vgpu_ppgtt_spt *s =
-			ppgtt_find_shadow_page(vgpu, ops->get_pfn(&e));
+			ppgtt_find_shadow_page(vgpu, ops->get_pfn(se));
 		if (!s) {
 			gvt_vgpu_err("fail to find guest page\n");
 			ret = -ENXIO;
@@ -1007,12 +1004,10 @@ static int ppgtt_handle_guest_entry_removal(struct intel_vgpu_guest_page *gpt,
 		if (ret)
 			goto fail;
 	}
-	ops->set_pfn(&e, vgpu->gtt.scratch_pt[sp->type].page_mfn);
-	ppgtt_set_shadow_entry(spt, &e, index);
 	return 0;
 fail:
 	gvt_vgpu_err("fail: shadow page %p guest entry 0x%llx type %d\n",
-			spt, e.val64, e.type);
+			spt, se->val64, se->type);
 	return ret;
 }
 
@@ -1232,22 +1227,37 @@ static int ppgtt_handle_guest_write_page_table(
 {
 	struct intel_vgpu_ppgtt_spt *spt = guest_page_to_ppgtt_spt(gpt);
 	struct intel_vgpu *vgpu = spt->vgpu;
+	int type = spt->shadow_page.type;
 	struct intel_gvt_gtt_pte_ops *ops = vgpu->gvt->gtt.pte_ops;
+	struct intel_gvt_gtt_entry se;
 
 	int ret;
 	int new_present;
 
 	new_present = ops->test_present(we);
 
-	ret = ppgtt_handle_guest_entry_removal(gpt, index);
-	if (ret)
-		goto fail;
+	/*
+	 * Adding the new entry first and then removing the old one, that can
+	 * guarantee the ppgtt table is validated during the window between
+	 * adding and removal.
+	 */
+	ppgtt_get_shadow_entry(spt, &se, index);
 
 	if (new_present) {
 		ret = ppgtt_handle_guest_entry_add(gpt, we, index);
 		if (ret)
 			goto fail;
 	}
+
+	ret = ppgtt_handle_guest_entry_removal(gpt, &se, index);
+	if (ret)
+		goto fail;
+
+	if (!new_present) {
+		ops->set_pfn(&se, vgpu->gtt.scratch_pt[type].page_mfn);
+		ppgtt_set_shadow_entry(spt, &se, index);
+	}
+
 	return 0;
 fail:
 	gvt_vgpu_err("fail: shadow page %p guest entry 0x%llx type %d.\n",
@@ -1319,7 +1329,7 @@ static int ppgtt_handle_guest_write_page_table_bytes(void *gp,
 	struct intel_vgpu *vgpu = spt->vgpu;
 	struct intel_gvt_gtt_pte_ops *ops = vgpu->gvt->gtt.pte_ops;
 	const struct intel_gvt_device_info *info = &vgpu->gvt->device_info;
-	struct intel_gvt_gtt_entry we;
+	struct intel_gvt_gtt_entry we, se;
 	unsigned long index;
 	int ret;
 
@@ -1335,7 +1345,8 @@ static int ppgtt_handle_guest_write_page_table_bytes(void *gp,
 			return ret;
 	} else {
 		if (!test_bit(index, spt->post_shadow_bitmap)) {
-			ret = ppgtt_handle_guest_entry_removal(gpt, index);
+			ppgtt_get_shadow_entry(spt, &se, index);
+			ret = ppgtt_handle_guest_entry_removal(gpt, &se, index);
 			if (ret)
 				return ret;
 		}
-- 
2.7.4