Date: Mon, 27 Apr 2026 11:38:55 +0000 From: Andrew Turner <andrew@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Cc: Sarah Walker <sarah.walker2@arm.com> Subject: git: c16c95192f01 - main - virtio_net: Use bus_dma for rxq/txq buffers Message-ID: <69ef4acf.1fcd2.4d4d3e54@gitrepo.freebsd.org>
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The branch main has been updated by andrew: URL: https://cgit.FreeBSD.org/src/commit/?id=c16c95192f01237a876eb7bc336e3bbda9310171 commit c16c95192f01237a876eb7bc336e3bbda9310171 Author: Sarah Walker <sarah.walker2@arm.com> AuthorDate: 2026-02-16 14:19:13 +0000 Commit: Andrew Turner <andrew@FreeBSD.org> CommitDate: 2026-04-27 11:37:53 +0000 virtio_net: Use bus_dma for rxq/txq buffers While the majority of virtio platforms will be fully coherent, some may require cache maintenance or other specific device memory handling (eg for secure partitioning). Using bus_dma allows for these usecases. The virtio buffers are marked as coherent; this should ensure that sync calls are no-ops in the common cases. Reviewed by: andrew Sponsored by: Arm Ltd Differential Revision: https://reviews.freebsd.org/D55492 --- sys/dev/virtio/network/if_vtnet.c | 275 ++++++++++++++++++++++++++++++++--- sys/dev/virtio/network/if_vtnetvar.h | 10 ++ 2 files changed, 268 insertions(+), 17 deletions(-) diff --git a/sys/dev/virtio/network/if_vtnet.c b/sys/dev/virtio/network/if_vtnet.c index ef01833b9e03..e88602a44664 100644 --- a/sys/dev/virtio/network/if_vtnet.c +++ b/sys/dev/virtio/network/if_vtnet.c @@ -96,6 +96,17 @@ #define VTNET_ETHER_ALIGN ETHER_ALIGN #endif +/* + * Worst case offset to ensure header doesn't share any cache lines with + * payload. + */ +#define VTNET_RX_BUFFER_HEADER_OFFSET 128 + +struct vtnet_rx_buffer_header { + bus_addr_t addr; + bus_dmamap_t dmap; +}; + static int vtnet_modevent(module_t, int, void *); static int vtnet_probe(device_t); @@ -384,6 +395,17 @@ MODULE_DEPEND(vtnet, netmap, 1, 1, 1); VIRTIO_SIMPLE_PNPINFO(vtnet, VIRTIO_ID_NETWORK, "VirtIO Networking Adapter"); +static struct vtnet_rx_buffer_header * +vtnet_mbuf_to_rx_buffer_header(struct vtnet_softc *sc, struct mbuf *m) +{ + if (VTNET_ETHER_ALIGN != 0 && sc->vtnet_hdr_size % 4 == 0) + return (struct vtnet_rx_buffer_header *)((uintptr_t)m->m_data - + VTNET_RX_BUFFER_HEADER_OFFSET - VTNET_ETHER_ALIGN); + else + return (struct vtnet_rx_buffer_header *)((uintptr_t)m->m_data - + VTNET_RX_BUFFER_HEADER_OFFSET); +} + static int vtnet_modevent(module_t mod __unused, int type, void *unused __unused) { @@ -457,6 +479,60 @@ vtnet_attach(device_t dev) goto fail; } + mtx_init(&sc->vtnet_rx_mtx, device_get_nameunit(dev), + "VirtIO Net RX lock", MTX_DEF); + + error = bus_dma_tag_create( + bus_get_dma_tag(dev), /* parent */ + sizeof(uint16_t), /* alignment */ + 0, /* boundary */ + BUS_SPACE_MAXADDR, /* lowaddr */ + BUS_SPACE_MAXADDR, /* highaddr */ + NULL, NULL, /* filter, filterarg */ + MJUM9BYTES, /* max request size */ + 1, /* max # segments */ + MJUM9BYTES, /* maxsegsize - worst case */ + BUS_DMA_COHERENT, /* flags */ + busdma_lock_mutex, /* lockfunc */ + &sc->vtnet_rx_mtx, /* lockarg */ + &sc->vtnet_rx_dmat); + if (error) { + device_printf(dev, "cannot create bus_dma_tag\n"); + goto fail; + } + + mtx_init(&sc->vtnet_tx_mtx, device_get_nameunit(dev), + "VirtIO Net TX lock", MTX_DEF); + + error = bus_dma_tag_create( + bus_get_dma_tag(dev), /* parent */ + sizeof(uint16_t), /* alignment */ + 0, /* boundary */ + BUS_SPACE_MAXADDR, /* lowaddr */ + BUS_SPACE_MAXADDR, /* highaddr */ + NULL, NULL, /* filter, filterarg */ + sc->vtnet_tx_nsegs * MJUM9BYTES, /* max request size */ + sc->vtnet_tx_nsegs, /* max # segments */ + MJUM9BYTES, /* maxsegsize */ + BUS_DMA_COHERENT, /* flags */ + busdma_lock_mutex, /* lockfunc */ + &sc->vtnet_tx_mtx, /* lockarg */ + &sc->vtnet_tx_dmat); + if (error) { + device_printf(dev, "cannot create bus_dma_tag\n"); + goto fail; + } + +#ifdef __powerpc__ + /* + * Virtio uses physical addresses rather than bus addresses, so we + * need to ask busdma to skip the iommu physical->bus mapping. At + * present, this is only a thing on the powerpc architectures. + */ + bus_dma_tag_set_iommu(sc->vtnet_rx_dmat, NULL, NULL); + bus_dma_tag_set_iommu(sc->vtnet_tx_dmat, NULL, NULL); +#endif + error = vtnet_alloc_rx_filters(sc); if (error) { device_printf(dev, "cannot allocate Rx filters\n"); @@ -1545,6 +1621,11 @@ static struct mbuf * vtnet_rx_alloc_buf(struct vtnet_softc *sc, int nbufs, struct mbuf **m_tailp) { struct mbuf *m_head, *m_tail, *m; + struct vtnet_rx_buffer_header *vthdr; + bus_dma_segment_t segs[1]; + bus_dmamap_t dmap; + int nsegs; + int err; int i, size; m_head = NULL; @@ -1562,13 +1643,43 @@ vtnet_rx_alloc_buf(struct vtnet_softc *sc, int nbufs, struct mbuf **m_tailp) } m->m_len = size; + vthdr = (struct vtnet_rx_buffer_header *)m->m_data; + + /* Reserve space for header */ + m_adj(m, VTNET_RX_BUFFER_HEADER_OFFSET); + /* * Need to offset the mbuf if the header we're going to add * will misalign. */ - if (VTNET_ETHER_ALIGN != 0 && sc->vtnet_hdr_size % 4 == 0) { + if (VTNET_ETHER_ALIGN != 0 && sc->vtnet_hdr_size % 4 == 0) m_adj(m, VTNET_ETHER_ALIGN); + + err = bus_dmamap_create(sc->vtnet_rx_dmat, 0, &dmap); + if (err) { + printf("Failed to create dmamap, err :%d\n", + err); + m_freem(m); + return (NULL); } + + nsegs = 0; + err = bus_dmamap_load_mbuf_sg(sc->vtnet_rx_dmat, dmap, m, segs, + &nsegs, BUS_DMA_NOWAIT); + if (err != 0) { + printf("Failed to map mbuf into DMA visible memory, err: %d\n", + err); + m_freem(m); + bus_dmamap_destroy(sc->vtnet_rx_dmat, dmap); + return (NULL); + } + KASSERT(nsegs == 1, + ("%s: unexpected number of DMA segments for rx buffer: %d", + __func__, nsegs)); + + vthdr->addr = segs[0].ds_addr; + vthdr->dmap = dmap; + if (m_head != NULL) { m_tail->m_next = m; m_tail = m; @@ -1594,7 +1705,7 @@ vtnet_rxq_replace_lro_nomrg_buf(struct vtnet_rxq *rxq, struct mbuf *m0, int len, clustersz, nreplace, error; sc = rxq->vtnrx_sc; - clustersz = sc->vtnet_rx_clustersz; + clustersz = sc->vtnet_rx_clustersz - VTNET_RX_BUFFER_HEADER_OFFSET; /* * Need to offset the mbuf if the header we're going to add will * misalign, account for that here. @@ -1709,9 +1820,12 @@ vtnet_rxq_replace_buf(struct vtnet_rxq *rxq, struct mbuf *m, int len) static int vtnet_rxq_enqueue_buf(struct vtnet_rxq *rxq, struct mbuf *m) { + struct vtnet_rx_buffer_header *hdr; struct vtnet_softc *sc; struct sglist *sg; int header_inlined, error; + bus_addr_t paddr; + struct mbuf *mp; sc = rxq->vtnrx_sc; sg = rxq->vtnrx_sg; @@ -1724,28 +1838,38 @@ vtnet_rxq_enqueue_buf(struct vtnet_rxq *rxq, struct mbuf *m) header_inlined = vtnet_modern(sc) || (sc->vtnet_flags & VTNET_FLAG_MRG_RXBUFS) != 0; /* TODO: ANY_LAYOUT */ + hdr = vtnet_mbuf_to_rx_buffer_header(sc, m); + paddr = hdr->addr; + /* * Note: The mbuf has been already adjusted when we allocate it if we * have to do strict alignment. */ - if (header_inlined) - error = sglist_append_mbuf(sg, m); - else { - struct vtnet_rx_header *rxhdr = - mtod(m, struct vtnet_rx_header *); + if (header_inlined) { + error = sglist_append_phys(sg, paddr, m->m_len); + } else { MPASS(sc->vtnet_hdr_size == sizeof(struct virtio_net_hdr)); /* Append the header and remaining mbuf data. */ - error = sglist_append(sg, &rxhdr->vrh_hdr, sc->vtnet_hdr_size); + error = sglist_append_phys(sg, paddr, sc->vtnet_hdr_size); if (error) return (error); - error = sglist_append(sg, &rxhdr[1], + error = sglist_append_phys(sg, + paddr + sizeof(struct vtnet_rx_header), m->m_len - sizeof(struct vtnet_rx_header)); if (error) return (error); - if (m->m_next != NULL) - error = sglist_append_mbuf(sg, m->m_next); + mp = m->m_next; + while (mp) { + hdr = vtnet_mbuf_to_rx_buffer_header(sc, mp); + paddr = hdr->addr; + error = sglist_append_phys(sg, paddr, mp->m_len); + if (error) + return (error); + + mp = mp->m_next; + } } if (error) @@ -1931,6 +2055,7 @@ vtnet_rxq_merged_eof(struct vtnet_rxq *rxq, struct mbuf *m_head, int nbufs) m_tail = m_head; while (--nbufs > 0) { + struct vtnet_rx_buffer_header *vthdr; struct mbuf *m; uint32_t len; @@ -1940,6 +2065,10 @@ vtnet_rxq_merged_eof(struct vtnet_rxq *rxq, struct mbuf *m_head, int nbufs) goto fail; } + vthdr = vtnet_mbuf_to_rx_buffer_header(sc, m); + bus_dmamap_sync(sc->vtnet_rx_dmat, vthdr->dmap, + BUS_DMASYNC_POSTREAD); + if (vtnet_rxq_new_buf(rxq) != 0) { rxq->vtnrx_stats.vrxs_iqdrops++; vtnet_rxq_discard_buf(rxq, m); @@ -2060,6 +2189,7 @@ static int vtnet_rxq_eof(struct vtnet_rxq *rxq) { struct virtio_net_hdr lhdr, *hdr; + struct vtnet_rx_buffer_header *vthdr; struct vtnet_softc *sc; if_t ifp; struct virtqueue *vq; @@ -2075,14 +2205,31 @@ vtnet_rxq_eof(struct vtnet_rxq *rxq) CURVNET_SET(if_getvnet(ifp)); while (count-- > 0) { - struct mbuf *m; + struct mbuf *m, *mp; uint32_t len, nbufs, adjsz; + uint32_t synced; m = virtqueue_dequeue(vq, &len); if (m == NULL) break; deq++; + mp = m; + + /* + * Sync all mbufs in this packet. There will only be a single + * mbuf unless LRO is in use. + */ + synced = 0; + while (mp && synced < len) { + vthdr = vtnet_mbuf_to_rx_buffer_header(sc, mp); + bus_dmamap_sync(sc->vtnet_rx_dmat, vthdr->dmap, + BUS_DMASYNC_POSTREAD); + + synced += mp->m_len; + mp = mp->m_next; + } + if (len < sc->vtnet_hdr_size + ETHER_HDR_LEN) { rxq->vtnrx_stats.vrxs_ierrors++; vtnet_rxq_discard_buf(rxq, m); @@ -2342,6 +2489,14 @@ vtnet_txq_free_mbufs(struct vtnet_txq *txq) while ((txhdr = virtqueue_drain(vq, &last)) != NULL) { if (kring == NULL) { + bus_dmamap_unload(txq->vtntx_sc->vtnet_tx_dmat, + txhdr->dmap); + bus_dmamap_destroy(txq->vtntx_sc->vtnet_tx_dmat, + txhdr->dmap); + bus_dmamap_unload(txq->vtntx_sc->vtnet_tx_dmat, + txhdr->hdr_dmap); + bus_dmamap_destroy(txq->vtntx_sc->vtnet_tx_dmat, + txhdr->hdr_dmap); m_freem(txhdr->vth_mbuf); uma_zfree(vtnet_tx_header_zone, txhdr); } @@ -2511,15 +2666,36 @@ drop: return (NULL); } +static void +vtnet_txq_enqueue_callback(void *arg, bus_dma_segment_t *segs, + int nsegs, int error) +{ + vm_paddr_t *hdr_paddr; + + if (error != 0) + return; + + KASSERT(nsegs == 1, ("%s: %d segments returned!", __func__, nsegs)); + + hdr_paddr = (vm_paddr_t *)arg; + *hdr_paddr = segs[0].ds_addr; +} + static int vtnet_txq_enqueue_buf(struct vtnet_txq *txq, struct mbuf **m_head, struct vtnet_tx_header *txhdr) { + bus_dma_segment_t segs[VTNET_TX_SEGS_MAX]; + int nsegs; struct vtnet_softc *sc; struct virtqueue *vq; struct sglist *sg; struct mbuf *m; int error; + vm_paddr_t hdr_paddr; + bus_dmamap_t hdr_dmap; + bus_dmamap_t dmap; + int i; sc = txq->vtntx_sc; vq = txq->vtntx_vq; @@ -2527,15 +2703,55 @@ vtnet_txq_enqueue_buf(struct vtnet_txq *txq, struct mbuf **m_head, m = *m_head; sglist_reset(sg); - error = sglist_append(sg, &txhdr->vth_uhdr, sc->vtnet_hdr_size); + + error = bus_dmamap_create(sc->vtnet_tx_dmat, 0, &hdr_dmap); + if (error) + goto fail; + + error = bus_dmamap_load(sc->vtnet_tx_dmat, hdr_dmap, &txhdr->vth_uhdr, + sc->vtnet_hdr_size, vtnet_txq_enqueue_callback, &hdr_paddr, + BUS_DMA_NOWAIT); + if (error) + goto fail_hdr_dmamap_destroy; + + error = sglist_append_phys(sg, hdr_paddr, sc->vtnet_hdr_size); if (error != 0 || sg->sg_nseg != 1) { KASSERT(0, ("%s: cannot add header to sglist error %d nseg %d", __func__, error, sg->sg_nseg)); - goto fail; + goto fail_hdr_dmamap_unload; } - error = sglist_append_mbuf(sg, m); + bus_dmamap_sync(sc->vtnet_tx_dmat, hdr_dmap, BUS_DMASYNC_PREWRITE); + + error = bus_dmamap_create(sc->vtnet_tx_dmat, 0, &dmap); + if (error) + goto fail_hdr_dmamap_unload; + + nsegs = 0; + error = bus_dmamap_load_mbuf_sg(sc->vtnet_tx_dmat, dmap, m, segs, + &nsegs, BUS_DMA_NOWAIT); + if (error != 0) + goto fail_dmamap_destroy; + KASSERT(nsegs <= sc->vtnet_tx_nsegs, + ("%s: unexpected number of DMA segments for tx buffer: %d (max %d)", + __func__, nsegs, sc->vtnet_tx_nsegs)); + + bus_dmamap_sync(sc->vtnet_tx_dmat, dmap, BUS_DMASYNC_PREWRITE); + + for (i = 0; i < nsegs && !error; i++) + error = sglist_append_phys(sg, segs[i].ds_addr, segs[i].ds_len); + if (error) { + sglist_reset(sg); + bus_dmamap_unload(sc->vtnet_tx_dmat, dmap); + + error = sglist_append_phys(sg, hdr_paddr, sc->vtnet_hdr_size); + if (error != 0 || sg->sg_nseg != 1) { + KASSERT(0, ("%s: cannot add header to sglist error %d nseg %d", + __func__, error, sg->sg_nseg)); + goto fail_dmamap_destroy; + } + m = m_defrag(m, M_NOWAIT); if (m == NULL) { sc->vtnet_stats.tx_defrag_failed++; @@ -2545,16 +2761,41 @@ vtnet_txq_enqueue_buf(struct vtnet_txq *txq, struct mbuf **m_head, *m_head = m; sc->vtnet_stats.tx_defragged++; - error = sglist_append_mbuf(sg, m); + nsegs = 0; + error = bus_dmamap_load_mbuf_sg(sc->vtnet_tx_dmat, dmap, m, + segs, &nsegs, BUS_DMA_NOWAIT); + if (error != 0) + goto fail_dmamap_destroy; + KASSERT(nsegs <= sc->vtnet_tx_nsegs, + ("%s: unexpected number of DMA segments for tx buffer: %d (max %d)", + __func__, nsegs, sc->vtnet_tx_nsegs)); + + bus_dmamap_sync(sc->vtnet_tx_dmat, dmap, BUS_DMASYNC_PREWRITE); + + for (i = 0; i < nsegs && !error; i++) + error = sglist_append_phys(sg, segs[i].ds_addr, + segs[i].ds_len); + if (error) - goto fail; + goto fail_dmamap_unload; } txhdr->vth_mbuf = m; + txhdr->dmap = dmap; + txhdr->hdr_dmap = hdr_dmap; + error = virtqueue_enqueue(vq, txhdr, sg, sg->sg_nseg, 0); return (error); +fail_dmamap_unload: + bus_dmamap_unload(sc->vtnet_tx_dmat, dmap); +fail_dmamap_destroy: + bus_dmamap_destroy(sc->vtnet_tx_dmat, dmap); +fail_hdr_dmamap_unload: + bus_dmamap_unload(sc->vtnet_tx_dmat, hdr_dmap); +fail_hdr_dmamap_destroy: + bus_dmamap_destroy(sc->vtnet_tx_dmat, hdr_dmap); fail: m_freem(*m_head); *m_head = NULL; diff --git a/sys/dev/virtio/network/if_vtnetvar.h b/sys/dev/virtio/network/if_vtnetvar.h index eb5e6784b07f..6cafe827d733 100644 --- a/sys/dev/virtio/network/if_vtnetvar.h +++ b/sys/dev/virtio/network/if_vtnetvar.h @@ -190,6 +190,12 @@ struct vtnet_softc { struct mtx vtnet_mtx; char vtnet_mtx_name[16]; uint8_t vtnet_hwaddr[ETHER_ADDR_LEN]; + + bus_dma_tag_t vtnet_rx_dmat; + struct mtx vtnet_rx_mtx; + + bus_dma_tag_t vtnet_tx_dmat; + struct mtx vtnet_tx_mtx; }; /* vtnet flag descriptions for use with printf(9) %b identifier. */ #define VTNET_FLAGS_BITS \ @@ -273,6 +279,10 @@ struct vtnet_tx_header { } vth_uhdr; struct mbuf *vth_mbuf; + + bus_dmamap_t dmap; + + bus_dmamap_t hdr_dmap; }; /*home | help
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