xen-netfront: purge page flipping support

Currently neither Linux nor FreeBSD netback supports page flipping. NetBSD
still supports that. It is not sure how many people actually use page
flipping, but page flipping is supposed to be slower than copying nowadays.
It will also shatter frontend / backend address space.

Overall this feature is more of a burden than a benefit.

Submitted by:		Wei Liu <wei.liu2@citrix.com>
Reviewed by:		royger
Differential Revision:	https://reviews.freebsd.org/D3888
Sponsored by:		Citrix Systems R&D

diff --git a/sys/dev/xen/netfront/netfront.c b/sys/dev/xen/netfront/netfront.c
index d53bfde2af01073063e26c0a084511b3e2dafc03..5ad8004dd0abcbbd8ad321ecb5ae22ece6e0ca2d 100644 (file)
--- a/sys/dev/xen/netfront/netfront.c
+++ b/sys/dev/xen/netfront/netfront.c
@@ -110,18 +110,6 @@ TUNABLE_INT("hw.xn.enable_lro", &xn_enable_lro);
 
 #endif
 
-#ifdef CONFIG_XEN
-static int MODPARM_rx_copy = 0;
-module_param_named(rx_copy, MODPARM_rx_copy, bool, 0);
-MODULE_PARM_DESC(rx_copy, "Copy packets from network card (rather than flip)");
-static int MODPARM_rx_flip = 0;
-module_param_named(rx_flip, MODPARM_rx_flip, bool, 0);
-MODULE_PARM_DESC(rx_flip, "Flip packets from network card (rather than copy)");
-#else
-static const int MODPARM_rx_copy = 1;
-static const int MODPARM_rx_flip = 0;
-#endif
-
 /**
  * \brief The maximum allowed data fragments in a single transmit
  *        request.
@@ -186,7 +174,7 @@ static void xn_free_tx_ring(struct netfront_info *);
 
 static int xennet_get_responses(struct netfront_info *np,
        struct netfront_rx_info *rinfo, RING_IDX rp, RING_IDX *cons,
-       struct mbuf **list, int *pages_flipped_p);
+       struct mbuf **list);
 
 #define virt_to_mfn(x) (vtophys(x) >> PAGE_SHIFT)
 
@@ -253,7 +241,6 @@ struct netfront_info {
        struct mtx   sc_lock;
 
        xen_intr_handle_t xen_intr_handle;
-       u_int copying_receiver;
        u_int carrier;
        u_int maxfrags;
 
@@ -551,8 +538,7 @@ talk_to_backend(device_t dev, struct netfront_info *info)
                message = "writing event-channel";
                goto abort_transaction;
        }
-       err = xs_printf(xst, node, "request-rx-copy", "%u",
-                       info->copying_receiver);
+       err = xs_printf(xst, node, "request-rx-copy", "%u", 1);
        if (err) {
                message = "writing request-rx-copy";
                goto abort_transaction;
@@ -792,9 +778,7 @@ network_alloc_rx_buffers(struct netfront_info *sc)
        struct mbuf *m_new;
        int i, batch_target, notify;
        RING_IDX req_prod;
-       struct xen_memory_reservation reservation;
        grant_ref_t ref;
-       int nr_flips;
        netif_rx_request_t *req;
        vm_offset_t vaddr;
        u_long pfn;
@@ -855,7 +839,7 @@ network_alloc_rx_buffers(struct netfront_info *sc)
        }
 
 refill:
-       for (nr_flips = i = 0; ; i++) {
+       for (i = 0; ; i++) {
                if ((m_new = mbufq_dequeue(&sc->xn_rx_batch)) == NULL)
                        break;
 
@@ -876,16 +860,7 @@ refill:
                pfn = vtophys(vaddr) >> PAGE_SHIFT;
                req = RING_GET_REQUEST(&sc->rx, req_prod + i);
 
-               if (sc->copying_receiver == 0) {
-                       gnttab_grant_foreign_transfer_ref(ref,
-                           otherend_id, pfn);
-                       sc->rx_pfn_array[nr_flips] = pfn;
-                       nr_flips++;
-               } else {
-                       gnttab_grant_foreign_access_ref(ref,
-                           otherend_id,
-                           pfn, 0);
-               }
+               gnttab_grant_foreign_access_ref(ref, otherend_id, pfn, 0);
                req->id = id;
                req->gref = ref;
 
@@ -899,19 +874,7 @@ refill:
         * We may have allocated buffers which have entries outstanding
         * in the page * update queue -- make sure we flush those first!
         */
-       if (nr_flips != 0) {
-#ifdef notyet
-               /* Tell the ballon driver what is going on. */
-               balloon_update_driver_allowance(i);
-#endif
-               set_xen_guest_handle(reservation.extent_start, sc->rx_pfn_array);
-               reservation.nr_extents   = i;
-               reservation.extent_order = 0;
-               reservation.address_bits = 0;
-               reservation.domid        = DOMID_SELF;
-       } else {
-               wmb();
-       }
+       wmb();
 
        /* Above is a suitable barrier to ensure backend will see requests. */
        sc->rx.req_prod_pvt = req_prod + i;
@@ -935,7 +898,7 @@ xn_rxeof(struct netfront_info *np)
        RING_IDX i, rp;
        struct mbuf *m;
        struct mbufq rxq, errq;
-       int err, pages_flipped = 0, work_to_do;
+       int err, work_to_do;
 
        do {
                XN_RX_LOCK_ASSERT(np);
@@ -957,8 +920,7 @@ xn_rxeof(struct netfront_info *np)
                        memset(extras, 0, sizeof(rinfo.extras));
 
                        m = NULL;
-                       err = xennet_get_responses(np, &rinfo, rp, &i, &m,
-                           &pages_flipped);
+                       err = xennet_get_responses(np, &rinfo, rp, &i, &m);
 
                        if (__predict_false(err)) {
                                if (m)
@@ -988,13 +950,6 @@ xn_rxeof(struct netfront_info *np)
                        np->rx.rsp_cons = i;
                }
 
-               if (pages_flipped) {
-                       /* Some pages are no longer absent... */
-#ifdef notyet
-                       balloon_update_driver_allowance(-pages_flipped);
-#endif
-               }
-
                mbufq_drain(&errq);
 
                /*
@@ -1227,10 +1182,8 @@ xennet_get_extras(struct netfront_info *np,
 static int
 xennet_get_responses(struct netfront_info *np,
        struct netfront_rx_info *rinfo, RING_IDX rp, RING_IDX *cons,
-       struct mbuf  **list,
-       int *pages_flipped_p)
+       struct mbuf  **list)
 {
-       int pages_flipped = *pages_flipped_p;
        struct netif_rx_response *rx = &rinfo->rx;
        struct netif_extra_info *extras = rinfo->extras;
        struct mbuf *m, *m0, *m_prev;
@@ -1252,8 +1205,6 @@ xennet_get_responses(struct netfront_info *np,
        }
 
        for (;;) {
-               u_long mfn;
-
 #if 0
                DPRINTK("rx->status=%hd rx->offset=%hu frags=%u\n",
                        rx->status, rx->offset, frags);
@@ -1290,23 +1241,8 @@ xennet_get_responses(struct netfront_info *np,
                        goto next;
                }
 
-               if (!np->copying_receiver) {
-                       /* Memory pressure, insufficient buffer
-                        * headroom, ...
-                        */
-                       if (!(mfn = gnttab_end_foreign_transfer_ref(ref))) {
-                               WPRINTK("Unfulfilled rx req (id=%d, st=%d).\n",
-                                       rx->id, rx->status);
-                               xennet_move_rx_slot(np, m, ref);
-                               err = ENOMEM;
-                               goto next;
-                       }
-
-                       pages_flipped++;
-               } else {
-                       ret = gnttab_end_foreign_access_ref(ref);
-                       KASSERT(ret, ("ret != 0"));
-               }
+               ret = gnttab_end_foreign_access_ref(ref);
+               KASSERT(ret, ("Unable to end access to grant references"));
 
                gnttab_release_grant_reference(&np->gref_rx_head, ref);
 
@@ -1359,7 +1295,6 @@ next_skip_queue:
        }
        *list = m0;
        *cons += frags;
-       *pages_flipped_p = pages_flipped;
 
        return (err);
 }
@@ -1815,24 +1750,16 @@ network_connect(struct netfront_info *np)
        int i, requeue_idx, error;
        grant_ref_t ref;
        netif_rx_request_t *req;
-       u_int feature_rx_copy, feature_rx_flip;
+       u_int feature_rx_copy;
 
        error = xs_scanf(XST_NIL, xenbus_get_otherend_path(np->xbdev),
            "feature-rx-copy", NULL, "%u", &feature_rx_copy);
        if (error)
                feature_rx_copy = 0;
-       error = xs_scanf(XST_NIL, xenbus_get_otherend_path(np->xbdev),
-           "feature-rx-flip", NULL, "%u", &feature_rx_flip);
-       if (error)
-               feature_rx_flip = 1;
 
-       /*
-        * Copy packets on receive path if:
-        *  (a) This was requested by user, and the backend supports it; or
-        *  (b) Flipping was requested, but this is unsupported by the backend.
-        */
-       np->copying_receiver = ((MODPARM_rx_copy && feature_rx_copy) ||
-                               (MODPARM_rx_flip && !feature_rx_flip));
+       /* We only support rx copy. */
+       if (!feature_rx_copy)
+               return (EPROTONOSUPPORT);
 
        /* Recovery procedure: */
        error = talk_to_backend(np->xbdev, np);
@@ -1858,15 +1785,10 @@ network_connect(struct netfront_info *np)
                req = RING_GET_REQUEST(&np->rx, requeue_idx);
                pfn = vtophys(mtod(m, vm_offset_t)) >> PAGE_SHIFT;
 
-               if (!np->copying_receiver) {
-                       gnttab_grant_foreign_transfer_ref(ref,
-                           xenbus_get_otherend_id(np->xbdev),
-                           pfn);
-               } else {
-                       gnttab_grant_foreign_access_ref(ref,
-                           xenbus_get_otherend_id(np->xbdev),
-                           pfn, 0);
-               }
+               gnttab_grant_foreign_access_ref(ref,
+                   xenbus_get_otherend_id(np->xbdev),
+                   pfn, 0);
+
                req->gref = ref;
                req->id   = requeue_idx;