xen-netfront: use gref mappings for Tx buffers

This is done in order to allow user to avoid grant paths,
by resorting to copying instead. Since we aren't guaranteed
to reuse pages on stack transmit, hence we can only reliably
copy to the Tx granted pages. Hence we keep a shadow pool and
use that instead. We don't require coalescing Tx requests, as
we already linearize the skb when required slots > available
slots.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: Shannon Nelson <shannon.nelson@oracle.com>
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Orabug: 26107942

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index baa87cb489904ac8c1e8be71c964013fd8973c9f..f36fc8f92968dde8462d721c9d7b9ecc5aa0a294 100644 (file)
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -510,6 +510,32 @@ static int xennet_open(struct net_device *dev)
        return 0;
 }
 
+static void xennet_tx_revoke_ref(struct netfront_queue *queue,
+                                unsigned short id)
+{
+       struct netfront_buffer_info *binfo = &queue->indir_tx;
+
+       if (binfo->bufs_num) {
+               unsigned short i = id;
+
+               if (binfo->bufs_num < NET_TX_RING_SIZE)
+                       i = i / binfo->bufs_num;
+               if (queue->grant_tx_ref[id] == binfo->bufs[i].ref)
+                       return;
+       }
+
+       if (unlikely(gnttab_query_foreign_access(
+               queue->grant_tx_ref[id]) != 0)) {
+               pr_alert("%s: warning -- grant still in use by backend domain\n",
+                        __func__);
+               BUG();
+       }
+       gnttab_end_foreign_access_ref(
+               queue->grant_tx_ref[id], GNTMAP_readonly);
+       gnttab_release_grant_reference(
+               &queue->gref_tx_head, queue->grant_tx_ref[id]);
+}
+
 static void xennet_tx_buf_gc(struct netfront_queue *queue)
 {
        RING_IDX cons, prod;
@@ -532,16 +558,7 @@ static void xennet_tx_buf_gc(struct netfront_queue *queue)
 
                        id  = txrsp->id;
                        skb = queue->tx_skbs[id].skb;
-                       if (unlikely(gnttab_query_foreign_access(
-                               queue->grant_tx_ref[id]) != 0)) {
-                               pr_alert("%s: warning -- grant still in use by backend domain\n",
-                                        __func__);
-                               BUG();
-                       }
-                       gnttab_end_foreign_access_ref(
-                               queue->grant_tx_ref[id], GNTMAP_readonly);
-                       gnttab_release_grant_reference(
-                               &queue->gref_tx_head, queue->grant_tx_ref[id]);
+                       xennet_tx_revoke_ref(queue, 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);
@@ -564,12 +581,34 @@ struct xennet_gnttab_make_txreq {
        unsigned int size;
 };
 
+static void *xennet_get_tx_buf(struct netfront_buffer_info *binfo,
+                              unsigned short i, unsigned int *size)
+{
+       u16 id, offset;
+
+       if (!binfo->bufs_num)
+               return NULL;
+
+       if (binfo->bufs_num < NET_TX_RING_SIZE) {
+               id = i / binfo->bufs_num;
+               *size = XEN_PAGE_SIZE / binfo->bufs_num;
+               offset = (i % binfo->bufs_num) * (*size);
+       } else {
+               id = i;
+               offset = 0;
+               *size = XEN_PAGE_SIZE;
+       }
+
+       return pfn_to_kaddr(page_to_pfn(binfo->bufs[id].page)) + offset;
+}
+
 static void xennet_tx_setup_grant(unsigned long gfn, unsigned int offset,
                                  unsigned int len, void *data)
 {
        struct xennet_gnttab_make_txreq *info = data;
-       unsigned int id;
        struct xen_netif_tx_request *tx;
+       unsigned int id, size = 0;
+       void *addr = NULL;
        grant_ref_t ref;
        /* convenient aliases */
        struct page *page = info->page;
@@ -578,11 +617,21 @@ static void xennet_tx_setup_grant(unsigned long gfn, unsigned int offset,
 
        id = get_id_from_freelist(&queue->tx_skb_freelist, queue->tx_skbs);
        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));
+       addr = xennet_get_tx_buf(&queue->indir_tx, id, &size);
+       if (!addr || len > size) {
+               ref = gnttab_claim_grant_reference(&queue->gref_tx_head);
+               WARN_ON_ONCE(IS_ERR_VALUE((unsigned long)(int)ref));
+
+               gnttab_grant_foreign_access_ref(ref,
+                                               queue->info->xbdev->otherend_id,
+                                               gfn, GNTMAP_readonly);
+       } else {
+               memcpy(addr + offset,
+                      pfn_to_kaddr(page_to_pfn(page)) + offset, len);
 
-       gnttab_grant_foreign_access_ref(ref, queue->info->xbdev->otherend_id,
-                                       gfn, GNTMAP_readonly);
+               page = queue->indir_tx.bufs[id].page;
+               ref = queue->indir_tx.bufs[id].ref;
+       }
 
        queue->tx_skbs[id].skb = skb;
        queue->grant_tx_page[id] = page;
@@ -1302,6 +1351,15 @@ static struct rtnl_link_stats64 *xennet_get_stats64(struct net_device *dev,
        return tot;
 }
 
+static void xennet_release_tx_single(struct netfront_queue *queue,
+                                    struct sk_buff *skb, unsigned short 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);
+       dev_kfree_skb_irq(skb);
+}
+
 static void xennet_release_tx_bufs(struct netfront_queue *queue)
 {
        struct sk_buff *skb;
@@ -1313,14 +1371,21 @@ static void xennet_release_tx_bufs(struct netfront_queue *queue)
                        continue;
 
                skb = queue->tx_skbs[i].skb;
+
+               /* The grant reference is instead revoked on
+                * xennet_deinit_grant_pool()
+                */
+               if (queue->indir_tx.bufs_num &&
+                   queue->grant_tx_ref[i] == queue->indir_tx.bufs[i].ref) {
+                       xennet_release_tx_single(queue, skb, i);
+                       continue;
+               }
+
                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);
-               dev_kfree_skb_irq(skb);
+               xennet_release_tx_single(queue, skb, i);
        }
 }