Date: Thu, 3 Nov 2022 12:37:34 GMT From: =?utf-8?Q?Roger=20Pau=20Monn=C3=A9?= <royger@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: dabb3db7a817 - main - xen/netfront: deal with mbuf data crossing a page boundary Message-ID: <202211031237.2A3CbYKV019751@gitrepo.freebsd.org>
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The branch main has been updated by royger: URL: https://cgit.FreeBSD.org/src/commit/?id=dabb3db7a817f003af3f89c965ba369c67fc4910 commit dabb3db7a817f003af3f89c965ba369c67fc4910 Author: Roger Pau Monné <royger@FreeBSD.org> AuthorDate: 2022-11-03 12:29:22 +0000 Commit: Roger Pau Monné <royger@FreeBSD.org> CommitDate: 2022-11-03 12:32:21 +0000 xen/netfront: deal with mbuf data crossing a page boundary There's been a report recently of mbufs with data that crosses a page boundary. It seems those mbufs are generated by the iSCSI target system: https://lists.xenproject.org/archives/html/xen-devel/2021-12/msg01581.html In order to handle those mbufs correctly on netfront use the bus_dma interface and explicitly request that segments must not cross a page boundary. No other requirements are necessary, so it's expected that bus_dma won't need to bounce the data and hence it shouldn't introduce a too big performance penalty. Using bus_dma requires some changes to netfront, mainly in order to accommodate for the fact that now ring slots no longer have a 1:1 match with mbufs, as a single mbuf can use two ring slots if the data buffer crosses a page boundary. Store the first packet of the mbuf chain in every ring slot that's used, and use a mbuf tag in order to store the bus_dma related structures and a refcount to keep track of the pending slots before the mbuf chain can be freed. Reported by: G.R. Tested by: G.R. MFC: 1 week Differential revision: https://reviews.freebsd.org/D33876 --- sys/dev/xen/netfront/netfront.c | 194 ++++++++++++++++++++++++++++------------ 1 file changed, 138 insertions(+), 56 deletions(-) diff --git a/sys/dev/xen/netfront/netfront.c b/sys/dev/xen/netfront/netfront.c index fc151453a49a..cfb6172dbe19 100644 --- a/sys/dev/xen/netfront/netfront.c +++ b/sys/dev/xen/netfront/netfront.c @@ -71,6 +71,8 @@ __FBSDID("$FreeBSD$"); #include <contrib/xen/io/netif.h> #include <xen/xenbus/xenbusvar.h> +#include <machine/bus.h> + #include "xenbus_if.h" /* Features supported by all backends. TSO and LRO can be negotiated */ @@ -126,7 +128,6 @@ static void xn_release_tx_bufs(struct netfront_txq *); static void xn_rxq_intr(struct netfront_rxq *); static void xn_txq_intr(struct netfront_txq *); static void xn_intr(void *); -static inline int xn_count_frags(struct mbuf *m); static int xn_assemble_tx_request(struct netfront_txq *, struct mbuf *); static int xn_ioctl(struct ifnet *, u_long, caddr_t); static void xn_ifinit_locked(struct netfront_info *); @@ -199,6 +200,17 @@ struct netfront_txq { struct taskqueue *tq; struct task defrtask; + bus_dma_segment_t segs[MAX_TX_REQ_FRAGS]; + struct mbuf_xennet { + struct m_tag tag; + bus_dma_tag_t dma_tag; + bus_dmamap_t dma_map; + struct netfront_txq *txq; + SLIST_ENTRY(mbuf_xennet) next; + u_int count; + } xennet_tag[NET_TX_RING_SIZE + 1]; + SLIST_HEAD(, mbuf_xennet) tags; + bool full; }; @@ -221,6 +233,8 @@ struct netfront_info { struct ifmedia sc_media; + bus_dma_tag_t dma_tag; + bool xn_reset; }; @@ -301,6 +315,42 @@ xn_get_rx_ref(struct netfront_rxq *rxq, RING_IDX ri) return (ref); } +#define MTAG_COOKIE 1218492000 +#define MTAG_XENNET 0 + +static void mbuf_grab(struct mbuf *m) +{ + struct mbuf_xennet *ref; + + ref = (struct mbuf_xennet *)m_tag_locate(m, MTAG_COOKIE, + MTAG_XENNET, NULL); + KASSERT(ref != NULL, ("Cannot find refcount")); + ref->count++; +} + +static void mbuf_release(struct mbuf *m) +{ + struct mbuf_xennet *ref; + + ref = (struct mbuf_xennet *)m_tag_locate(m, MTAG_COOKIE, + MTAG_XENNET, NULL); + KASSERT(ref != NULL, ("Cannot find refcount")); + KASSERT(ref->count > 0, ("Invalid reference count")); + + if (--ref->count == 0) + m_freem(m); +} + +static void tag_free(struct m_tag *t) +{ + struct mbuf_xennet *ref = (struct mbuf_xennet *)t; + + KASSERT(ref->count == 0, ("Free mbuf tag with pending refcnt")); + bus_dmamap_sync(ref->dma_tag, ref->dma_map, BUS_DMASYNC_POSTWRITE); + bus_dmamap_destroy(ref->dma_tag, ref->dma_map); + SLIST_INSERT_HEAD(&ref->txq->tags, ref, next); +} + #define IPRINTK(fmt, args...) \ printf("[XEN] " fmt, ##args) #ifdef INVARIANTS @@ -778,11 +828,18 @@ disconnect_txq(struct netfront_txq *txq) static void destroy_txq(struct netfront_txq *txq) { + unsigned int i; free(txq->ring.sring, M_DEVBUF); buf_ring_free(txq->br, M_DEVBUF); taskqueue_drain_all(txq->tq); taskqueue_free(txq->tq); + + for (i = 0; i <= NET_TX_RING_SIZE; i++) { + bus_dmamap_destroy(txq->info->dma_tag, + txq->xennet_tag[i].dma_map); + txq->xennet_tag[i].dma_map = NULL; + } } static void @@ -822,10 +879,27 @@ setup_txqs(device_t dev, struct netfront_info *info, mtx_init(&txq->lock, txq->name, "netfront transmit lock", MTX_DEF); + SLIST_INIT(&txq->tags); for (i = 0; i <= NET_TX_RING_SIZE; i++) { txq->mbufs[i] = (void *) ((u_long) i+1); txq->grant_ref[i] = GRANT_REF_INVALID; + txq->xennet_tag[i].txq = txq; + txq->xennet_tag[i].dma_tag = info->dma_tag; + error = bus_dmamap_create(info->dma_tag, 0, + &txq->xennet_tag[i].dma_map); + if (error != 0) { + device_printf(dev, + "failed to allocate dma map\n"); + goto fail; + } + m_tag_setup(&txq->xennet_tag[i].tag, + MTAG_COOKIE, MTAG_XENNET, + sizeof(txq->xennet_tag[i]) - + sizeof(txq->xennet_tag[i].tag)); + txq->xennet_tag[i].tag.m_tag_free = &tag_free; + SLIST_INSERT_HEAD(&txq->tags, &txq->xennet_tag[i], + next); } txq->mbufs[NET_TX_RING_SIZE] = (void *)0; @@ -1041,7 +1115,7 @@ xn_release_tx_bufs(struct netfront_txq *txq) if (txq->mbufs_cnt < 0) { panic("%s: tx_chain_cnt must be >= 0", __func__); } - m_free(m); + mbuf_release(m); } } @@ -1311,7 +1385,7 @@ xn_txeof(struct netfront_txq *txq) txq->mbufs[id] = NULL; add_id_to_freelist(txq->mbufs, id); txq->mbufs_cnt--; - m_free(m); + mbuf_release(m); /* Only mark the txq active if we've freed up at least one slot to try */ ifp->if_drv_flags &= ~IFF_DRV_OACTIVE; } @@ -1507,22 +1581,6 @@ next_skip_queue: return (err); } -/** - * \brief Count the number of fragments in an mbuf chain. - * - * Surprisingly, there isn't an M* macro for this. - */ -static inline int -xn_count_frags(struct mbuf *m) -{ - int nfrags; - - for (nfrags = 0; m != NULL; m = m->m_next) - nfrags++; - - return (nfrags); -} - /** * Given an mbuf chain, make sure we have enough room and then push * it onto the transmit ring. @@ -1530,46 +1588,50 @@ xn_count_frags(struct mbuf *m) static int xn_assemble_tx_request(struct netfront_txq *txq, struct mbuf *m_head) { - struct mbuf *m; struct netfront_info *np = txq->info; struct ifnet *ifp = np->xn_ifp; - u_int nfrags; - int otherend_id; + int otherend_id, error, nfrags; + bus_dma_segment_t *segs = txq->segs; + struct mbuf_xennet *tag; + bus_dmamap_t map; + unsigned int i; - /** - * Defragment the mbuf if necessary. - */ - nfrags = xn_count_frags(m_head); + KASSERT(!SLIST_EMPTY(&txq->tags), ("no tags available")); + tag = SLIST_FIRST(&txq->tags); + SLIST_REMOVE_HEAD(&txq->tags, next); + KASSERT(tag->count == 0, ("tag already in-use")); + map = tag->dma_map; + error = bus_dmamap_load_mbuf_sg(np->dma_tag, map, m_head, segs, + &nfrags, 0); + if (error == EFBIG || nfrags > np->maxfrags) { + struct mbuf *m; - /* - * Check to see whether this request is longer than netback - * can handle, and try to defrag it. - */ - /** - * It is a bit lame, but the netback driver in Linux can't - * deal with nfrags > MAX_TX_REQ_FRAGS, which is a quirk of - * the Linux network stack. - */ - if (nfrags > np->maxfrags) { + bus_dmamap_unload(np->dma_tag, map); m = m_defrag(m_head, M_NOWAIT); if (!m) { /* * Defrag failed, so free the mbuf and * therefore drop the packet. */ + SLIST_INSERT_HEAD(&txq->tags, tag, next); m_freem(m_head); return (EMSGSIZE); } m_head = m; + error = bus_dmamap_load_mbuf_sg(np->dma_tag, map, m_head, segs, + &nfrags, 0); + if (error != 0 || nfrags > np->maxfrags) { + bus_dmamap_unload(np->dma_tag, map); + SLIST_INSERT_HEAD(&txq->tags, tag, next); + m_freem(m_head); + return (error ?: EFBIG); + } + } else if (error != 0) { + SLIST_INSERT_HEAD(&txq->tags, tag, next); + m_freem(m_head); + return (error); } - /* Determine how many fragments now exist */ - nfrags = xn_count_frags(m_head); - - /* - * Check to see whether the defragmented packet has too many - * segments for the Linux netback driver. - */ /** * The FreeBSD TCP stack, with TSO enabled, can produce a chain * of mbufs longer than Linux can handle. Make sure we don't @@ -1583,6 +1645,8 @@ xn_assemble_tx_request(struct netfront_txq *txq, struct mbuf *m_head) "won't be able to handle it, dropping\n", __func__, nfrags, MAX_TX_REQ_FRAGS); #endif + SLIST_INSERT_HEAD(&txq->tags, tag, next); + bus_dmamap_unload(np->dma_tag, map); m_freem(m_head); return (EMSGSIZE); } @@ -1604,9 +1668,9 @@ xn_assemble_tx_request(struct netfront_txq *txq, struct mbuf *m_head) * the fragment pointers. Stop when we run out * of fragments or hit the end of the mbuf chain. */ - m = m_head; otherend_id = xenbus_get_otherend_id(np->xbdev); - for (m = m_head; m; m = m->m_next) { + m_tag_prepend(m_head, &tag->tag); + for (i = 0; i < nfrags; i++) { netif_tx_request_t *tx; uintptr_t id; grant_ref_t ref; @@ -1621,17 +1685,20 @@ xn_assemble_tx_request(struct netfront_txq *txq, struct mbuf *m_head) if (txq->mbufs_cnt > NET_TX_RING_SIZE) panic("%s: tx_chain_cnt must be <= NET_TX_RING_SIZE\n", __func__); - txq->mbufs[id] = m; + mbuf_grab(m_head); + txq->mbufs[id] = m_head; tx->id = id; ref = gnttab_claim_grant_reference(&txq->gref_head); KASSERT((short)ref >= 0, ("Negative ref")); - mfn = virt_to_mfn(mtod(m, vm_offset_t)); + mfn = atop(segs[i].ds_addr); gnttab_grant_foreign_access_ref(ref, otherend_id, mfn, GNTMAP_readonly); tx->gref = txq->grant_ref[id] = ref; - tx->offset = mtod(m, vm_offset_t) & (PAGE_SIZE - 1); + tx->offset = segs[i].ds_addr & PAGE_MASK; + KASSERT(tx->offset + segs[i].ds_len <= PAGE_SIZE, + ("mbuf segment crosses a page boundary")); tx->flags = 0; - if (m == m_head) { + if (i == 0) { /* * The first fragment has the entire packet * size, subsequent fragments have just the @@ -1640,7 +1707,7 @@ xn_assemble_tx_request(struct netfront_txq *txq, struct mbuf *m_head) * subtracting the sizes of the other * fragments. */ - tx->size = m->m_pkthdr.len; + tx->size = m_head->m_pkthdr.len; /* * The first fragment contains the checksum flags @@ -1654,12 +1721,12 @@ xn_assemble_tx_request(struct netfront_txq *txq, struct mbuf *m_head) * so we have to test for CSUM_TSO * explicitly. */ - if (m->m_pkthdr.csum_flags + if (m_head->m_pkthdr.csum_flags & (CSUM_DELAY_DATA | CSUM_TSO)) { tx->flags |= (NETTXF_csum_blank | NETTXF_data_validated); } - if (m->m_pkthdr.csum_flags & CSUM_TSO) { + if (m_head->m_pkthdr.csum_flags & CSUM_TSO) { struct netif_extra_info *gso = (struct netif_extra_info *) RING_GET_REQUEST(&txq->ring, @@ -1667,7 +1734,7 @@ xn_assemble_tx_request(struct netfront_txq *txq, struct mbuf *m_head) tx->flags |= NETTXF_extra_info; - gso->u.gso.size = m->m_pkthdr.tso_segsz; + gso->u.gso.size = m_head->m_pkthdr.tso_segsz; gso->u.gso.type = XEN_NETIF_GSO_TYPE_TCPV4; gso->u.gso.pad = 0; @@ -1677,13 +1744,14 @@ xn_assemble_tx_request(struct netfront_txq *txq, struct mbuf *m_head) gso->flags = 0; } } else { - tx->size = m->m_len; + tx->size = segs[i].ds_len; } - if (m->m_next) + if (i != nfrags - 1) tx->flags |= NETTXF_more_data; txq->ring.req_prod_pvt++; } + bus_dmamap_sync(np->dma_tag, map, BUS_DMASYNC_PREWRITE); BPF_MTAP(ifp, m_head); if_inc_counter(ifp, IFCOUNTER_OPACKETS, 1); @@ -2244,7 +2312,20 @@ create_netdev(device_t dev) ether_ifattach(ifp, np->mac); netfront_carrier_off(np); - return (0); + err = bus_dma_tag_create( + bus_get_dma_tag(dev), /* parent */ + 1, PAGE_SIZE, /* algnmnt, boundary */ + BUS_SPACE_MAXADDR, /* lowaddr */ + BUS_SPACE_MAXADDR, /* highaddr */ + NULL, NULL, /* filter, filterarg */ + PAGE_SIZE * MAX_TX_REQ_FRAGS, /* max request size */ + MAX_TX_REQ_FRAGS, /* max segments */ + PAGE_SIZE, /* maxsegsize */ + BUS_DMA_ALLOCNOW, /* flags */ + NULL, NULL, /* lockfunc, lockarg */ + &np->dma_tag); + + return (err); error: KASSERT(err != 0, ("Error path with no error code specified")); @@ -2277,6 +2358,7 @@ netif_free(struct netfront_info *np) if_free(np->xn_ifp); np->xn_ifp = NULL; ifmedia_removeall(&np->sc_media); + bus_dma_tag_destroy(np->dma_tag); } static void
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