--- zzzz-none-000/linux-3.10.107/crypto/scatterwalk.c	2017-06-27 09:49:32.000000000 +0000
+++ scorpion-7490-727/linux-3.10.107/crypto/scatterwalk.c	2021-02-04 17:41:59.000000000 +0000
@@ -54,7 +54,11 @@
 		struct page *page;
 
 		page = sg_page(walk->sg) + ((walk->offset - 1) >> PAGE_SHIFT);
-		if (!PageSlab(page))
+		/* Test ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE first as
+		 * PageSlab cannot be optimised away per se due to
+		 * use of volatile pointer.
+		 */
+		if (ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE && !PageSlab(page))
 			flush_dcache_page(page);
 	}
 
@@ -62,7 +66,7 @@
 		walk->offset += PAGE_SIZE - 1;
 		walk->offset &= PAGE_MASK;
 		if (walk->offset >= walk->sg->offset + walk->sg->length)
-			scatterwalk_start(walk, scatterwalk_sg_next(walk->sg));
+			scatterwalk_start(walk, sg_next(walk->sg));
 	}
 }
 
@@ -105,23 +109,64 @@
 			      unsigned int start, unsigned int nbytes, int out)
 {
 	struct scatter_walk walk;
-	unsigned int offset = 0;
+	struct scatterlist tmp[2];
 
 	if (!nbytes)
 		return;
 
+	sg = scatterwalk_ffwd(tmp, sg, start);
+
+	if (sg_page(sg) == virt_to_page(buf) &&
+	    sg->offset == offset_in_page(buf))
+		return;
+
+	scatterwalk_start(&walk, sg);
+	scatterwalk_copychunks(buf, &walk, nbytes, out);
+	scatterwalk_done(&walk, out, 0);
+}
+EXPORT_SYMBOL_GPL(scatterwalk_map_and_copy);
+
+int scatterwalk_bytes_sglen(struct scatterlist *sg, int num_bytes)
+{
+	int offset = 0, n = 0;
+
+	/* num_bytes is too small */
+	if (num_bytes < sg->length)
+		return -1;
+
+	do {
+		offset += sg->length;
+		n++;
+		sg = sg_next(sg);
+
+		/* num_bytes is too large */
+		if (unlikely(!sg && (num_bytes < offset)))
+			return -1;
+	} while (sg && (num_bytes > offset));
+
+	return n;
+}
+EXPORT_SYMBOL_GPL(scatterwalk_bytes_sglen);
+
+struct scatterlist *scatterwalk_ffwd(struct scatterlist dst[2],
+				     struct scatterlist *src,
+				     unsigned int len)
+{
 	for (;;) {
-		scatterwalk_start(&walk, sg);
+		if (!len)
+			return src;
 
-		if (start < offset + sg->length)
+		if (src->length > len)
 			break;
 
-		offset += sg->length;
-		sg = scatterwalk_sg_next(sg);
+		len -= src->length;
+		src = sg_next(src);
 	}
 
-	scatterwalk_advance(&walk, start - offset);
-	scatterwalk_copychunks(buf, &walk, nbytes, out);
-	scatterwalk_done(&walk, out, 0);
+	sg_init_table(dst, 2);
+	sg_set_page(dst, sg_page(src), src->length - len, src->offset + len);
+	scatterwalk_crypto_chain(dst, sg_next(src), 0, 2);
+
+	return dst;
 }
-EXPORT_SYMBOL_GPL(scatterwalk_map_and_copy);
+EXPORT_SYMBOL_GPL(scatterwalk_ffwd);