drm/i915/gvt: support inconsecutive partial gtt entry write

Previously we assumed two 4-byte writes to the same PTE coming in sequence.
But recently we observed inconsecutive partial write happening as well. So
this patch enhances the previous solution. It now uses a list to save more
partial writes. If one partial write can be combined with another one in
the list to construct a full PTE, update its shadow entry. Otherwise, save
the partial write in the list.

v2: invalidate old entry and flush ggtt (Zhenyu)
v3: split old ggtt page unmap to another patch (Zhenyu)
v4: refine codes (Zhenyu)
Signed-off-by: Hang Yuan <hang.yuan@linux.intel.com>
Cc: Yan Zhao <yan.y.zhao@intel.com>
Cc: Xiaolin Zhang <xiaolin.zhang@intel.com>
Cc: Zhenyu Wang <zhenyu.z.wang@intel.com>
Reviewed-by: Xiaolin Zhang <xiaolin.zhang@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

drivers/gpu/drm/i915/gvt/gtt.c

@@ -1901,7 +1901,6 @@ static struct intel_vgpu_mm *intel_vgpu_create_ggtt_mm(struct intel_vgpu *vgpu)
 		vgpu_free_mm(mm);
 		return ERR_PTR(-ENOMEM);
 	}
-	mm->ggtt_mm.last_partial_off = -1UL;
 
 	return mm;
 }
@@ -1926,7 +1925,6 @@ void _intel_vgpu_mm_release(struct kref *mm_ref)
 		invalidate_ppgtt_mm(mm);
 	} else {
 		vfree(mm->ggtt_mm.virtual_ggtt);
-		mm->ggtt_mm.last_partial_off = -1UL;
 	}
 
 	vgpu_free_mm(mm);
@@ -2164,6 +2162,8 @@ static int emulate_ggtt_mmio_write(struct intel_vgpu *vgpu, unsigned int off,
 	struct intel_gvt_gtt_entry e, m;
 	dma_addr_t dma_addr;
 	int ret;
+	struct intel_gvt_partial_pte *partial_pte, *pos, *n;
+	bool partial_update = false;
 
 	if (bytes != 4 && bytes != 8)
 		return -EINVAL;
@@ -2174,68 +2174,57 @@ static int emulate_ggtt_mmio_write(struct intel_vgpu *vgpu, unsigned int off,
 	if (!vgpu_gmadr_is_valid(vgpu, gma))
 		return 0;
 
-	ggtt_get_guest_entry(ggtt_mm, &e, g_gtt_index);
-
+	e.type = GTT_TYPE_GGTT_PTE;
 	memcpy((void *)&e.val64 + (off & (info->gtt_entry_size - 1)), p_data,
 			bytes);
 
 	/* If ggtt entry size is 8 bytes, and it's split into two 4 bytes
-	 * write, we assume the two 4 bytes writes are consecutive.
-	 * Otherwise, we abort and report error
+	 * write, save the first 4 bytes in a list and update virtual
+	 * PTE. Only update shadow PTE when the second 4 bytes comes.
 	 */
 	if (bytes < info->gtt_entry_size) {
-		if (ggtt_mm->ggtt_mm.last_partial_off == -1UL) {
-			/* the first partial part*/
-			ggtt_mm->ggtt_mm.last_partial_off = off;
-			ggtt_mm->ggtt_mm.last_partial_data = e.val64;
-			return 0;
-		} else if ((g_gtt_index ==
-				(ggtt_mm->ggtt_mm.last_partial_off >>
-				info->gtt_entry_size_shift)) &&
-			(off !=	ggtt_mm->ggtt_mm.last_partial_off)) {
-			/* the second partial part */
-
-			int last_off = ggtt_mm->ggtt_mm.last_partial_off &
-				(info->gtt_entry_size - 1);
-
-			memcpy((void *)&e.val64 + last_off,
-				(void *)&ggtt_mm->ggtt_mm.last_partial_data +
-				last_off, bytes);
-
-			ggtt_mm->ggtt_mm.last_partial_off = -1UL;
-		} else {
-			int last_offset;
-
-			gvt_vgpu_err("failed to populate guest ggtt entry: abnormal ggtt entry write sequence, last_partial_off=%lx, offset=%x, bytes=%d, ggtt entry size=%d\n",
-					ggtt_mm->ggtt_mm.last_partial_off, off,
-					bytes, info->gtt_entry_size);
-
-			/* set host ggtt entry to scratch page and clear
-			 * virtual ggtt entry as not present for last
-			 * partially write offset
-			 */
-			last_offset = ggtt_mm->ggtt_mm.last_partial_off &
-					(~(info->gtt_entry_size - 1));
-
-			ggtt_get_host_entry(ggtt_mm, &m, last_offset);
-			ggtt_invalidate_pte(vgpu, &m);
-			ops->set_pfn(&m, gvt->gtt.scratch_mfn);
-			ops->clear_present(&m);
-			ggtt_set_host_entry(ggtt_mm, &m, last_offset);
-			ggtt_invalidate(gvt->dev_priv);
-
-			ggtt_get_guest_entry(ggtt_mm, &e, last_offset);
-			ops->clear_present(&e);
-			ggtt_set_guest_entry(ggtt_mm, &e, last_offset);
-
-			ggtt_mm->ggtt_mm.last_partial_off = off;
-			ggtt_mm->ggtt_mm.last_partial_data = e.val64;
+		bool found = false;
+
+		list_for_each_entry_safe(pos, n,
+				&ggtt_mm->ggtt_mm.partial_pte_list, list) {
+			if (g_gtt_index == pos->offset >>
+					info->gtt_entry_size_shift) {
+				if (off != pos->offset) {
+					/* the second partial part*/
+					int last_off = pos->offset &
+						(info->gtt_entry_size - 1);
+
+					memcpy((void *)&e.val64 + last_off,
+						(void *)&pos->data + last_off,
+						bytes);
+
+					list_del(&pos->list);
+					kfree(pos);
+					found = true;
+					break;
+				}
+
+				/* update of the first partial part */
+				pos->data = e.val64;
+				ggtt_set_guest_entry(ggtt_mm, &e, g_gtt_index);
+				return 0;
+			}
+		}
 
-			return 0;
+		if (!found) {
+			/* the first partial part */
+			partial_pte = kzalloc(sizeof(*partial_pte), GFP_KERNEL);
+			if (!partial_pte)
+				return -ENOMEM;
+			partial_pte->offset = off;
+			partial_pte->data = e.val64;
+			list_add_tail(&partial_pte->list,
+				&ggtt_mm->ggtt_mm.partial_pte_list);
+			partial_update = true;
 		}
 	}
 
-	if (ops->test_present(&e)) {
+	if (!partial_update && (ops->test_present(&e))) {
 		gfn = ops->get_pfn(&e);
 		m = e;
 
@@ -2428,6 +2417,8 @@ int intel_vgpu_init_gtt(struct intel_vgpu *vgpu)
 
 	intel_vgpu_reset_ggtt(vgpu, false);
 
+	INIT_LIST_HEAD(&gtt->ggtt_mm->ggtt_mm.partial_pte_list);
+
 	return create_scratch_page_tree(vgpu);
 }
 
@@ -2452,6 +2443,14 @@ static void intel_vgpu_destroy_all_ppgtt_mm(struct intel_vgpu *vgpu)
 
 static void intel_vgpu_destroy_ggtt_mm(struct intel_vgpu *vgpu)
 {
+	struct intel_gvt_partial_pte *pos;
+
+	list_for_each_entry(pos,
+			&vgpu->gtt.ggtt_mm->ggtt_mm.partial_pte_list, list) {
+		gvt_dbg_mm("partial PTE update on hold 0x%lx : 0x%llx\n",
+			pos->offset, pos->data);
+		kfree(pos);
+	}
 	intel_vgpu_destroy_mm(vgpu->gtt.ggtt_mm);
 	vgpu->gtt.ggtt_mm = NULL;
 }

drivers/gpu/drm/i915/gvt/gtt.h

@@ -133,6 +133,12 @@ enum intel_gvt_mm_type {
 
 #define GVT_RING_CTX_NR_PDPS	GEN8_3LVL_PDPES
 
+struct intel_gvt_partial_pte {
+	unsigned long offset;
+	u64 data;
+	struct list_head list;
+};
+
 struct intel_vgpu_mm {
 	enum intel_gvt_mm_type type;
 	struct intel_vgpu *vgpu;
@@ -157,8 +163,7 @@ struct intel_vgpu_mm {
 		} ppgtt_mm;
 		struct {
 			void *virtual_ggtt;
-			unsigned long last_partial_off;
-			u64 last_partial_data;
+			struct list_head partial_pte_list;
 		} ggtt_mm;
 	};
 };