lib/scatterlist: Fix to calculate the last_pg properly

The last_pg is wrong, it is actually the first page of the last scatterlist element. To get the last page of the last scatterlist element we have to add prv->length. So it is checking mergability against the wrong page, Further, a SG element is not guaranteed to end on a page boundary, so we have to check the sub page location also for merge eligibility. Fix the above by checking physical contiguity based on PFNs, compute the actual last page and then call pages_are_mergable(). Fixes: 1567b49 ("lib/scatterlist: add check when merging zone device pages") Link: https://lore.kernel.org/r/[email protected] Reported-by: Jason Gunthorpe <[email protected]> Signed-off-by: Yishai Hadas <[email protected]> Reviewed-by: Chaitanya Kulkarni <[email protected]> Signed-off-by: Jason Gunthorpe <[email protected]>
Kleist · Jan 16, 2023 · 0f097f0 · 0f097f0
1 parent b3deec2
commit 0f097f0
Showing 1 changed file with 15 additions and 10 deletions.
diff --git a/lib/scatterlist.c b/lib/scatterlist.c
@@ -470,22 +470,27 @@ int sg_alloc_append_table_from_pages(struct sg_append_table *sgt_append,
 		return -EOPNOTSUPP;
 
 	if (sgt_append->prv) {
+		unsigned long next_pfn = (page_to_phys(sg_page(sgt_append->prv)) +
+			sgt_append->prv->offset + sgt_append->prv->length) / PAGE_SIZE;
+
 		if (WARN_ON(offset))
 			return -EINVAL;
 
 		/* Merge contiguous pages into the last SG */
 		prv_len = sgt_append->prv->length;
-		last_pg = sg_page(sgt_append->prv);
-		while (n_pages && pages_are_mergeable(pages[0], last_pg)) {
-			if (sgt_append->prv->length + PAGE_SIZE > max_segment)
-				break;
-			sgt_append->prv->length += PAGE_SIZE;
-			last_pg = pages[0];
-			pages++;
-			n_pages--;
+		if (page_to_pfn(pages[0]) == next_pfn) {
+			last_pg = pfn_to_page(next_pfn - 1);
+			while (n_pages && pages_are_mergeable(pages[0], last_pg)) {
+				if (sgt_append->prv->length + PAGE_SIZE > max_segment)
+					break;
+				sgt_append->prv->length += PAGE_SIZE;
+				last_pg = pages[0];
+				pages++;
+				n_pages--;
+			}
+			if (!n_pages)
+				goto out;
 		}
-		if (!n_pages)
-			goto out;
 	}
 
 	/* compute number of contiguous chunks */