This is a note to let you know that I've just added the patch titled xen/netfront: disentangle tx_skb_freelist to the 5.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: xen-netfront-disentangle-tx_skb_freelist.patch and it can be found in the queue-5.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From foo@baz Mon Nov 29 05:38:48 PM CET 2021 From: Juergen Gross <jgross@xxxxxxxx> Date: Mon, 29 Nov 2021 09:03:28 +0100 Subject: xen/netfront: disentangle tx_skb_freelist From: Juergen Gross <jgross@xxxxxxxx> commit 21631d2d741a64a073e167c27769e73bc7844a2f upstream. The tx_skb_freelist elements are in a single linked list with the request id used as link reference. The per element link field is in a union with the skb pointer of an in use request. Move the link reference out of the union in order to enable a later reuse of it for requests which need a populated skb pointer. Rename add_id_to_freelist() and get_id_from_freelist() to add_id_to_list() and get_id_from_list() in order to prepare using those for other lists as well. Define ~0 as value to indicate the end of a list and place that value into the link for a request not being on the list. When freeing a skb zero the skb pointer in the request. Use a NULL value of the skb pointer instead of skb_entry_is_link() for deciding whether a request has a skb linked to it. Remove skb_entry_set_link() and open code it instead as it is really trivial now. Signed-off-by: Juergen Gross <jgross@xxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/net/xen-netfront.c | 61 ++++++++++++++++++--------------------------- 1 file changed, 25 insertions(+), 36 deletions(-) --- a/drivers/net/xen-netfront.c +++ b/drivers/net/xen-netfront.c @@ -121,17 +121,11 @@ struct netfront_queue { /* * {tx,rx}_skbs store outstanding skbuffs. Free tx_skb entries - * are linked from tx_skb_freelist through skb_entry.link. - * - * NB. Freelist index entries are always going to be less than - * PAGE_OFFSET, whereas pointers to skbs will always be equal or - * greater than PAGE_OFFSET: we use this property to distinguish - * them. + * are linked from tx_skb_freelist through tx_link. */ - union skb_entry { - struct sk_buff *skb; - unsigned long link; - } tx_skbs[NET_TX_RING_SIZE]; + struct sk_buff *tx_skbs[NET_TX_RING_SIZE]; + unsigned short tx_link[NET_TX_RING_SIZE]; +#define TX_LINK_NONE 0xffff grant_ref_t gref_tx_head; grant_ref_t grant_tx_ref[NET_TX_RING_SIZE]; struct page *grant_tx_page[NET_TX_RING_SIZE]; @@ -169,33 +163,25 @@ struct netfront_rx_info { struct xen_netif_extra_info extras[XEN_NETIF_EXTRA_TYPE_MAX - 1]; }; -static void skb_entry_set_link(union skb_entry *list, unsigned short id) -{ - list->link = id; -} - -static int skb_entry_is_link(const union skb_entry *list) -{ - BUILD_BUG_ON(sizeof(list->skb) != sizeof(list->link)); - return (unsigned long)list->skb < PAGE_OFFSET; -} - /* * Access macros for acquiring freeing slots in tx_skbs[]. */ -static void add_id_to_freelist(unsigned *head, union skb_entry *list, - unsigned short id) +static void add_id_to_list(unsigned *head, unsigned short *list, + unsigned short id) { - skb_entry_set_link(&list[id], *head); + list[id] = *head; *head = id; } -static unsigned short get_id_from_freelist(unsigned *head, - union skb_entry *list) +static unsigned short get_id_from_list(unsigned *head, unsigned short *list) { unsigned int id = *head; - *head = list[id].link; + + if (id != TX_LINK_NONE) { + *head = list[id]; + list[id] = TX_LINK_NONE; + } return id; } @@ -394,7 +380,8 @@ static void xennet_tx_buf_gc(struct netf continue; id = txrsp.id; - skb = queue->tx_skbs[id].skb; + skb = queue->tx_skbs[id]; + queue->tx_skbs[id] = NULL; if (unlikely(gnttab_query_foreign_access( queue->grant_tx_ref[id]) != 0)) { pr_alert("%s: warning -- grant still in use by backend domain\n", @@ -407,7 +394,7 @@ static void xennet_tx_buf_gc(struct netf &queue->gref_tx_head, queue->grant_tx_ref[id]); queue->grant_tx_ref[id] = GRANT_INVALID_REF; queue->grant_tx_page[id] = NULL; - add_id_to_freelist(&queue->tx_skb_freelist, queue->tx_skbs, id); + add_id_to_list(&queue->tx_skb_freelist, queue->tx_link, id); dev_kfree_skb_irq(skb); } @@ -440,7 +427,7 @@ static void xennet_tx_setup_grant(unsign struct netfront_queue *queue = info->queue; struct sk_buff *skb = info->skb; - id = get_id_from_freelist(&queue->tx_skb_freelist, queue->tx_skbs); + id = get_id_from_list(&queue->tx_skb_freelist, queue->tx_link); tx = RING_GET_REQUEST(&queue->tx, queue->tx.req_prod_pvt++); ref = gnttab_claim_grant_reference(&queue->gref_tx_head); WARN_ON_ONCE(IS_ERR_VALUE((unsigned long)(int)ref)); @@ -448,7 +435,7 @@ static void xennet_tx_setup_grant(unsign gnttab_grant_foreign_access_ref(ref, queue->info->xbdev->otherend_id, gfn, GNTMAP_readonly); - queue->tx_skbs[id].skb = skb; + queue->tx_skbs[id] = skb; queue->grant_tx_page[id] = page; queue->grant_tx_ref[id] = ref; @@ -1129,17 +1116,18 @@ static void xennet_release_tx_bufs(struc for (i = 0; i < NET_TX_RING_SIZE; i++) { /* Skip over entries which are actually freelist references */ - if (skb_entry_is_link(&queue->tx_skbs[i])) + if (!queue->tx_skbs[i]) continue; - skb = queue->tx_skbs[i].skb; + skb = queue->tx_skbs[i]; + queue->tx_skbs[i] = NULL; get_page(queue->grant_tx_page[i]); gnttab_end_foreign_access(queue->grant_tx_ref[i], GNTMAP_readonly, (unsigned long)page_address(queue->grant_tx_page[i])); queue->grant_tx_page[i] = NULL; queue->grant_tx_ref[i] = GRANT_INVALID_REF; - add_id_to_freelist(&queue->tx_skb_freelist, queue->tx_skbs, i); + add_id_to_list(&queue->tx_skb_freelist, queue->tx_link, i); dev_kfree_skb_irq(skb); } } @@ -1621,13 +1609,14 @@ static int xennet_init_queue(struct netf snprintf(queue->name, sizeof(queue->name), "vif%s-q%u", devid, queue->id); - /* Initialise tx_skbs as a free chain containing every entry. */ + /* Initialise tx_skb_freelist as a free chain containing every entry. */ queue->tx_skb_freelist = 0; for (i = 0; i < NET_TX_RING_SIZE; i++) { - skb_entry_set_link(&queue->tx_skbs[i], i+1); + queue->tx_link[i] = i + 1; queue->grant_tx_ref[i] = GRANT_INVALID_REF; queue->grant_tx_page[i] = NULL; } + queue->tx_link[NET_TX_RING_SIZE - 1] = TX_LINK_NONE; /* Clear out rx_skbs */ for (i = 0; i < NET_RX_RING_SIZE; i++) { Patches currently in stable-queue which might be from jgross@xxxxxxxx are queue-5.4/xen-blkfront-read-response-from-backend-only-once.patch queue-5.4/tty-hvc-replace-bug_on-with-negative-return-value.patch queue-5.4/xen-blkfront-don-t-trust-the-backend-response-data-blindly.patch queue-5.4/xen-sync-include-xen-interface-io-ring.h-with-xen-s-newest-version.patch queue-5.4/xen-blkfront-don-t-take-local-copy-of-a-request-from-the-ring-page.patch queue-5.4/xen-detect-uninitialized-xenbus-in-xenbus_init.patch queue-5.4/xen-netfront-don-t-read-data-from-request-on-the-ring-page.patch queue-5.4/xen-netfront-disentangle-tx_skb_freelist.patch queue-5.4/xen-netfront-read-response-from-backend-only-once.patch queue-5.4/xen-netfront-don-t-trust-the-backend-response-data-blindly.patch