xen-netback: handle page straddling in xenvif_set_hash_mapping()

There's no guarantee that the mapping array doesn't cross a page
boundary. Use a second grant copy operation if necessary.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/xen-netback/hash.c

@@ -334,28 +334,39 @@ u32 xenvif_set_hash_mapping(struct xenvif *vif, u32 gref, u32 len,
 			    u32 off)
 {
 	u32 *mapping = vif->hash.mapping[!vif->hash.mapping_sel];
-	struct gnttab_copy copy_op = {
+	unsigned int nr = 1;
+	struct gnttab_copy copy_op[2] = {{
 		.source.u.ref = gref,
 		.source.domid = vif->domid,
 		.dest.domid = DOMID_SELF,
 		.len = len * sizeof(*mapping),
 		.flags = GNTCOPY_source_gref
-	};
+	}};
 
 	if ((off + len < off) || (off + len > vif->hash.size) ||
 	    len > XEN_PAGE_SIZE / sizeof(*mapping))
 		return XEN_NETIF_CTRL_STATUS_INVALID_PARAMETER;
 
-	copy_op.dest.u.gmfn = virt_to_gfn(mapping + off);
-	copy_op.dest.offset = xen_offset_in_page(mapping + off);
+	copy_op[0].dest.u.gmfn = virt_to_gfn(mapping + off);
+	copy_op[0].dest.offset = xen_offset_in_page(mapping + off);
+	if (copy_op[0].dest.offset + copy_op[0].len > XEN_PAGE_SIZE) {
+		copy_op[1] = copy_op[0];
+		copy_op[1].source.offset = XEN_PAGE_SIZE - copy_op[0].dest.offset;
+		copy_op[1].dest.u.gmfn = virt_to_gfn(mapping + off + len);
+		copy_op[1].dest.offset = 0;
+		copy_op[1].len = copy_op[0].len - copy_op[1].source.offset;
+		copy_op[0].len = copy_op[1].source.offset;
+		nr = 2;
+	}
 
 	memcpy(mapping, vif->hash.mapping[vif->hash.mapping_sel],
 	       vif->hash.size * sizeof(*mapping));
 
-	if (copy_op.len != 0) {
-		gnttab_batch_copy(&copy_op, 1);
+	if (copy_op[0].len != 0) {
+		gnttab_batch_copy(copy_op, nr);
 
-		if (copy_op.status != GNTST_okay)
+		if (copy_op[0].status != GNTST_okay ||
+		    copy_op[nr - 1].status != GNTST_okay)
 			return XEN_NETIF_CTRL_STATUS_INVALID_PARAMETER;
 	}