[PATCH net-next v6 7/10] xen-netback: Handle guests with too many frags
From: Zoltan Kiss
Date: Tue Mar 04 2014 - 17:33:38 EST
Xen network protocol had implicit dependency on MAX_SKB_FRAGS. Netback has to
handle guests sending up to XEN_NETBK_LEGACY_SLOTS_MAX slots. To achieve that:
- create a new skb
- map the leftover slots to its frags (no linear buffer here!)
- chain it to the previous through skb_shinfo(skb)->frag_list
- map them
- copy and coalesce the frags into a brand new one and send it to the stack
- unmap the 2 old skb's pages
NOTE: if bisect brought you here, you should apply the series up until #9,
otherwise malicious guests can block other guests by not releasing their sent
packets.
Signed-off-by: Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>
---
v3:
- adding extra check for frag number
- consolidate alloc_skb's into xenvif_alloc_skb()
- BUG_ON(frag_overflow > MAX_SKB_FRAGS)
v4:
- handle error of skb_copy_expand()
v5:
- ratelimit error messages
- remove a tx_flags setting from xenvif_tx_submit
v6:
- move out handling from tx_submit into a new funciont, as it became quite long
- skb_copy[_expand] allocate a new skb with a huge linear buffer, which is bad
in times of memory pressure. Just make a new frags array and do the copy and
coalesce with skb_copy_bits
drivers/net/xen-netback/netback.c | 172 ++++++++++++++++++++++++++++++++++---
1 file changed, 162 insertions(+), 10 deletions(-)
diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index 447d58a..b284851 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -37,6 +37,7 @@
#include <linux/kthread.h>
#include <linux/if_vlan.h>
#include <linux/udp.h>
+#include <linux/highmem.h>
#include <net/tcp.h>
@@ -792,6 +793,23 @@ static inline void xenvif_tx_create_gop(struct xenvif *vif,
sizeof(*txp));
}
+static inline struct sk_buff *xenvif_alloc_skb(unsigned int size)
+{
+ struct sk_buff *skb =
+ alloc_skb(size + NET_SKB_PAD + NET_IP_ALIGN,
+ GFP_ATOMIC | __GFP_NOWARN);
+ if (unlikely(skb == NULL))
+ return NULL;
+
+ /* Packets passed to netif_rx() must have some headroom. */
+ skb_reserve(skb, NET_SKB_PAD + NET_IP_ALIGN);
+
+ /* Initialize it here to avoid later surprises */
+ skb_shinfo(skb)->destructor_arg = NULL;
+
+ return skb;
+}
+
static struct gnttab_map_grant_ref *xenvif_get_requests(struct xenvif *vif,
struct sk_buff *skb,
struct xen_netif_tx_request *txp,
@@ -802,11 +820,16 @@ static struct gnttab_map_grant_ref *xenvif_get_requests(struct xenvif *vif,
u16 pending_idx = *((u16 *)skb->cb);
int start;
pending_ring_idx_t index;
- unsigned int nr_slots;
+ unsigned int nr_slots, frag_overflow = 0;
/* At this point shinfo->nr_frags is in fact the number of
* slots, which can be as large as XEN_NETBK_LEGACY_SLOTS_MAX.
*/
+ if (shinfo->nr_frags > MAX_SKB_FRAGS) {
+ frag_overflow = shinfo->nr_frags - MAX_SKB_FRAGS;
+ BUG_ON(frag_overflow > MAX_SKB_FRAGS);
+ shinfo->nr_frags = MAX_SKB_FRAGS;
+ }
nr_slots = shinfo->nr_frags;
/* Skip first skb fragment if it is on same page as header fragment. */
@@ -822,6 +845,30 @@ static struct gnttab_map_grant_ref *xenvif_get_requests(struct xenvif *vif,
BUG_ON(shinfo->nr_frags > MAX_SKB_FRAGS);
+ if (frag_overflow) {
+ struct sk_buff *nskb = xenvif_alloc_skb(0);
+ if (unlikely(nskb == NULL)) {
+ if (net_ratelimit())
+ netdev_err(vif->dev,
+ "Can't allocate the frag_list skb.\n");
+ return NULL;
+ }
+
+ shinfo = skb_shinfo(nskb);
+ frags = shinfo->frags;
+
+ for (shinfo->nr_frags = 0; shinfo->nr_frags < frag_overflow;
+ shinfo->nr_frags++, txp++, gop++) {
+ index = pending_index(vif->pending_cons++);
+ pending_idx = vif->pending_ring[index];
+ xenvif_tx_create_gop(vif, pending_idx, txp, gop);
+ frag_set_pending_idx(&frags[shinfo->nr_frags],
+ pending_idx);
+ }
+
+ skb_shinfo(skb)->frag_list = nskb;
+ }
+
return gop;
}
@@ -862,6 +909,7 @@ static int xenvif_tx_check_gop(struct xenvif *vif,
struct pending_tx_info *tx_info;
int nr_frags = shinfo->nr_frags;
int i, err, start;
+ struct sk_buff *first_skb = NULL;
/* Check status of header. */
err = gop->status;
@@ -873,6 +921,7 @@ static int xenvif_tx_check_gop(struct xenvif *vif,
/* Skip first skb fragment if it is on same page as header fragment. */
start = (frag_get_pending_idx(&shinfo->frags[0]) == pending_idx);
+check_frags:
for (i = start; i < nr_frags; i++) {
int j, newerr;
@@ -896,9 +945,11 @@ static int xenvif_tx_check_gop(struct xenvif *vif,
/* Not the first error? Preceding frags already invalidated. */
if (err)
continue;
-
/* First error: invalidate header and preceding fragments. */
- pending_idx = *((u16 *)skb->cb);
+ if (!first_skb)
+ pending_idx = *((u16 *)skb->cb);
+ else
+ pending_idx = *((u16 *)first_skb->cb);
xenvif_idx_unmap(vif, pending_idx);
for (j = start; j < i; j++) {
pending_idx = frag_get_pending_idx(&shinfo->frags[j]);
@@ -909,6 +960,32 @@ static int xenvif_tx_check_gop(struct xenvif *vif,
err = newerr;
}
+ if (skb_has_frag_list(skb)) {
+ first_skb = skb;
+ skb = shinfo->frag_list;
+ shinfo = skb_shinfo(skb);
+ nr_frags = shinfo->nr_frags;
+ start = 0;
+
+ goto check_frags;
+ }
+
+ /* There was a mapping error in the frag_list skb. We have to unmap
+ * the first skb's frags
+ */
+ if (first_skb && err) {
+ int j;
+ shinfo = skb_shinfo(first_skb);
+ pending_idx = *((u16 *)first_skb->cb);
+ start = (frag_get_pending_idx(&shinfo->frags[0]) == pending_idx);
+ for (j = start; j < shinfo->nr_frags; j++) {
+ pending_idx = frag_get_pending_idx(&shinfo->frags[j]);
+ xenvif_idx_unmap(vif, pending_idx);
+ xenvif_idx_release(vif, pending_idx,
+ XEN_NETIF_RSP_OKAY);
+ }
+ }
+
*gopp = gop + 1;
return err;
}
@@ -921,7 +998,7 @@ static void xenvif_fill_frags(struct xenvif *vif, struct sk_buff *skb)
u16 prev_pending_idx = INVALID_PENDING_IDX;
if (skb_shinfo(skb)->destructor_arg)
- prev_pending_idx = skb->cb;
+ prev_pending_idx = *((u16 *)skb->cb);
for (i = 0; i < nr_frags; i++) {
skb_frag_t *frag = shinfo->frags + i;
@@ -1160,8 +1237,7 @@ static unsigned xenvif_tx_build_gops(struct xenvif *vif, int budget)
ret < XEN_NETBK_LEGACY_SLOTS_MAX) ?
PKT_PROT_LEN : txreq.size;
- skb = alloc_skb(data_len + NET_SKB_PAD + NET_IP_ALIGN,
- GFP_ATOMIC | __GFP_NOWARN);
+ skb = xenvif_alloc_skb(data_len);
if (unlikely(skb == NULL)) {
netdev_dbg(vif->dev,
"Can't allocate a skb in start_xmit.\n");
@@ -1169,9 +1245,6 @@ static unsigned xenvif_tx_build_gops(struct xenvif *vif, int budget)
break;
}
- /* Packets passed to netif_rx() must have some headroom. */
- skb_reserve(skb, NET_SKB_PAD + NET_IP_ALIGN);
-
if (extras[XEN_NETIF_EXTRA_TYPE_GSO - 1].type) {
struct xen_netif_extra_info *gso;
gso = &extras[XEN_NETIF_EXTRA_TYPE_GSO - 1];
@@ -1222,6 +1295,75 @@ static unsigned xenvif_tx_build_gops(struct xenvif *vif, int budget)
return gop - vif->tx_map_ops;
}
+/* Consolidate skb with a frag_list into a brand new one with local pages on
+ * frags. Returns 0 or -ENOMEM if can't allocate new pages.
+ */
+static int xenvif_handle_frag_list(struct xenvif *vif, struct sk_buff *skb)
+{
+ unsigned int offset = skb_headlen(skb);
+ skb_frag_t frags[MAX_SKB_FRAGS];
+ int i;
+ struct ubuf_info *uarg;
+ struct sk_buff *nskb = skb_shinfo(skb)->frag_list;
+
+ vif->tx_zerocopy_sent += 2;
+ vif->tx_frag_overflow++;
+
+ xenvif_fill_frags(vif, nskb);
+ /* Subtract frags size, we will correct it later */
+ skb->truesize -= skb->data_len;
+ skb->len += nskb->len;
+ skb->data_len += nskb->len;
+
+ /* create a brand new frags array and coalesce there */
+ for (i = 0; offset < skb->len; i++) {
+ struct page *page;
+ void *vaddr;
+ unsigned int len;
+
+ BUG_ON(i >= MAX_SKB_FRAGS);
+ page = alloc_page(GFP_ATOMIC|__GFP_COLD);
+ if (!page) {
+ int j;
+ skb->truesize += skb->data_len;
+ for (j = 0; j < i; j++)
+ put_page(frags[j].page.p);
+ return -ENOMEM;
+ }
+
+ vaddr = kmap_atomic(page);
+ if (offset + PAGE_SIZE < skb->len)
+ len = PAGE_SIZE;
+ else
+ len = skb->len - offset;
+ if (skb_copy_bits(skb, offset, vaddr, len))
+ BUG();
+
+ kunmap_atomic(vaddr);
+ offset += len;
+ frags[i].page.p = page;
+ frags[i].page_offset = 0;
+ skb_frag_size_set(&frags[i], len);
+
+ }
+ /* swap out with old one */
+ memcpy(skb_shinfo(skb)->frags,
+ frags,
+ i * sizeof(skb_frag_t));
+ skb_shinfo(skb)->nr_frags = i;
+ skb->truesize += i * PAGE_SIZE;
+
+ /* remove traces of mapped pages and frag_list */
+ skb_frag_list_init(skb);
+ uarg = skb_shinfo(skb)->destructor_arg;
+ uarg->callback(uarg, true);
+ skb_shinfo(skb)->destructor_arg = NULL;
+
+ skb_shinfo(nskb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
+ kfree_skb(nskb);
+
+ return 0;
+}
static int xenvif_tx_submit(struct xenvif *vif)
{
@@ -1258,7 +1400,6 @@ static int xenvif_tx_submit(struct xenvif *vif)
&vif->pending_tx_info[pending_idx].callback_struct;
} else {
/* Schedule a response immediately. */
- skb_shinfo(skb)->destructor_arg = NULL;
xenvif_idx_unmap(vif, pending_idx);
}
@@ -1269,6 +1410,17 @@ static int xenvif_tx_submit(struct xenvif *vif)
xenvif_fill_frags(vif, skb);
+ if (unlikely(skb_has_frag_list(skb))) {
+ if (xenvif_handle_frag_list(vif, skb)) {
+ if (net_ratelimit())
+ netdev_err(vif->dev,
+ "Not enough memory to consolidate frag_list!\n");
+ skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
+ kfree_skb(skb);
+ continue;
+ }
+ }
+
if (skb_is_nonlinear(skb) && skb_headlen(skb) < PKT_PROT_LEN) {
int target = min_t(int, skb->len, PKT_PROT_LEN);
__pskb_pull_tail(skb, target - skb_headlen(skb));
--
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