[PATCH] netback: handle non-netback foreign pages

[PATCH] netback: handle non-netback foreign pages

[Ian Campbell]

# HG changeset patch
# User Ian Campbell <ian.campbell@citrix.com>
# Date 1229596950 0
# Node ID 376283b531465c4adb2cd88e452e6ced52628dbb
# Parent  ff9683032b76f533509191bb9532df10cbb9830b
netback: handle non-netback foreign pages

An SKB can contain pages which are foreign but not tracked by netback,
such as those created by gnttab_copy_grant_page when in
NETBK_DELAYED_COPY_SKB mode. These pages do not have a mapping field
which points to a valid offset in the pending_tx_info array.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>

diff -r ff9683032b76 -r 376283b53146 drivers/xen/netback/netback.c
--- a/drivers/xen/netback/netback.c	Sat Dec 13 16:00:43 2008 +0000
+++ b/drivers/xen/netback/netback.c	Thu Dec 18 10:42:30 2008 +0000
@@ -40,9 +40,6 @@
 
 /*define NETBE_DEBUG_INTERRUPT*/
 
-/* extra field used in struct page */
-#define netif_page_index(pg) (*(long *)&(pg)->mapping)
-
 struct netbk_rx_meta {
 	skb_frag_t frag;
 	int id;
@@ -87,6 +84,26 @@ static inline unsigned long idx_to_kaddr
 static inline unsigned long idx_to_kaddr(unsigned int idx)
 {
 	return (unsigned long)pfn_to_kaddr(idx_to_pfn(idx));
+}
+
+/* extra field used in struct page */
+static inline void netif_set_page_index(struct page *pg, long index)
+{
+	BUG_ON(index < 0);
+	*((long *)&(pg->mapping)) = index;
+}
+
+static inline long netif_page_index(struct page *pg)
+{
+	long idx = (*(long *)&(pg)->mapping);
+
+	if (!PageForeign(pg))
+		return -1;
+
+	if (mmap_pages[idx] != pg)
+		return -1;
+
+	return idx;
 }
 
 #define PKT_PROT_LEN 64
@@ -370,6 +387,7 @@ static u16 netbk_gop_frag(netif_t *netif
 	multicall_entry_t *mcl;
 	netif_rx_request_t *req;
 	unsigned long old_mfn, new_mfn;
+	long idx = netif_page_index(page);
 
 	old_mfn = virt_to_mfn(page_address(page));
 
@@ -380,9 +398,8 @@ static u16 netbk_gop_frag(netif_t *netif
 		meta->copy = 1;
 		copy_gop = npo->copy + npo->copy_prod++;
 		copy_gop->flags = GNTCOPY_dest_gref;
-		if (PageForeign(page)) {
-			struct pending_tx_info *src_pend =
-				&pending_tx_info[netif_page_index(page)];
+		if (idx > -1) {
+			struct pending_tx_info *src_pend = &pending_tx_info[idx];
 			copy_gop->source.domid = src_pend->netif->domid;
 			copy_gop->source.u.ref = src_pend->req.gref;
 			copy_gop->flags |= GNTCOPY_source_gref;
@@ -1437,8 +1454,10 @@ static void netif_idx_release(u16 pendin
 
 static void netif_page_release(struct page *page, unsigned int order)
 {
+	long idx = netif_page_index(page);
 	BUG_ON(order);
-	netif_idx_release(netif_page_index(page));
+	BUG_ON(idx < 0);
+	netif_idx_release(idx);
 }
 
 irqreturn_t netif_be_int(int irq, void *dev_id, struct pt_regs *regs)
@@ -1572,7 +1591,7 @@ static int __init netback_init(void)
 	for (i = 0; i < MAX_PENDING_REQS; i++) {
 		page = mmap_pages[i];
 		SetPageForeign(page, netif_page_release);
-		netif_page_index(page) = i;
+		netif_set_page_index(page, i);
 		INIT_LIST_HEAD(&pending_inuse[i].list);
 	}