From: Jan Klemkow Subject: Re: vmd: add checksum offload for guests To: Alexander Bluhm Cc: tech@openbsd.org Date: Sat, 24 May 2025 05:33:55 +0200 On Thu, May 22, 2025 at 11:14:12AM +0900, Alexander Bluhm wrote: > On Wed, May 21, 2025 at 03:38:16AM +0200, Jan Klemkow wrote: > > Hi, > > > > This diff uses the tun(4) offload capabilities in the virtio > > implementation of vmd(8). vmd(8) translates the virtio_net_hdr > > structures from the guests packets to tun_hdr for tun(4) and vice versa. > > The offloading features bits are dynamically negotiated with the guest. > > So, legacy guests are still working with this feature. The pledge part > > was discussed with deraadt. > > > > ok? > > With this diff Linux VM guests running on vmd(8) cannot use network > anymore. Yes, turns out a bug was introduces into my diff, while I rebased this diff in my git repository on top of a cvs branch. Anyway, the version below works again. ok? Thanks, Jan Index: sys/kern/kern_pledge.c =================================================================== RCS file: /cvs/src/sys/kern/kern_pledge.c,v diff -u -p -r1.323 kern_pledge.c --- sys/kern/kern_pledge.c 12 Feb 2025 14:11:26 -0000 1.323 +++ sys/kern/kern_pledge.c 24 May 2025 02:58:50 -0000 @@ -46,6 +46,7 @@ #include #include #include +#include #include #include #include @@ -1342,6 +1343,12 @@ pledge_ioctl(struct proc *p, long com, s (cdevsw[major(vp->v_rdev)].d_open == vmmopen)) { error = pledge_ioctl_vmm(p, com); if (error == 0) + return 0; + } + if ((fp->f_type == DTYPE_VNODE) && + (vp->v_type == VCHR) && + (cdevsw[major(vp->v_rdev)].d_open == tapopen)) { + if (com == TUNSCAP) return 0; } } Index: usr.sbin/vmd/vionet.c =================================================================== RCS file: /cvs/src/usr.sbin/vmd/vionet.c,v diff -u -p -r1.23 vionet.c --- usr.sbin/vmd/vionet.c 12 May 2025 17:17:42 -0000 1.23 +++ usr.sbin/vmd/vionet.c 24 May 2025 03:19:32 -0000 @@ -17,12 +17,18 @@ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */ #include +#include #include #include #include +#include #include +#include +#include +#include +#include #include #include @@ -33,11 +39,14 @@ #include #include #include +#include #include "atomicio.h" #include "virtio.h" #include "vmd.h" +#define VIRTIO_NET_F_CSUM (1 << 0) +#define VIRTIO_NET_F_GUEST_CSUM (1 << 1) #define VIRTIO_NET_F_MAC (1 << 5) #define RXQ 0 #define TXQ 1 @@ -54,7 +63,7 @@ static void *rx_run_loop(void *); static void *tx_run_loop(void *); static int vionet_rx(struct vionet_dev *, int); static ssize_t vionet_rx_copy(struct vionet_dev *, int, const struct iovec *, - int, size_t); + int, size_t, struct tun_hdr *th); static ssize_t vionet_rx_zerocopy(struct vionet_dev *, int, const struct iovec *, int); static void vionet_rx_event(int, short, void *); @@ -70,6 +79,10 @@ static void read_pipe_rx(int, short, voi static void read_pipe_tx(int, short, void *); static void vionet_assert_pic_irq(struct virtio_dev *); static void vionet_deassert_pic_irq(struct virtio_dev *); +static void vhdr2thdr(struct virtio_net_hdr *, struct tun_hdr *, + const struct iovec *, int); +static void thdr2vhdr(struct tun_hdr *, struct virtio_net_hdr *, + const struct iovec *, int); /* Device Globals */ struct event ev_tap; @@ -101,6 +114,7 @@ vionet_main(int fd, int fd_vmm) struct vm_create_params *vcp; ssize_t sz; int ret; + struct tun_capabilities tcap; /* * stdio - needed for read/write to disk fds and channels to the vm. @@ -132,6 +146,13 @@ vionet_main(int fd, int fd_vmm) ", vmm fd = %d", __func__, vionet->data_fd, dev.sync_fd, dev.async_fd, fd_vmm); + /* + * IFCAPs are tweaked after feature negotiation with the guest later. + */ + memset(&tcap, 0, sizeof(tcap)); + if (ioctl(vionet->data_fd, TUNSCAP, &tcap) == -1) + fatal("tap(4) TUNSCAP"); + /* Receive our vm information from the vm process. */ memset(&vm, 0, sizeof(vm)); sz = atomicio(read, dev.sync_fd, &vm, sizeof(vm)); @@ -156,7 +177,7 @@ vionet_main(int fd, int fd_vmm) * We no longer need /dev/vmm access. */ close_fd(fd_vmm); - if (pledge("stdio", NULL) == -1) + if (pledge("stdio vmm", NULL) == -1) fatal("pledge2"); /* If we're restoring hardware, re-initialize virtqueue hva's. */ @@ -315,6 +336,25 @@ fail: } /* + * Update and sync offload features with tap(4). + */ +static void +vionet_update_offload(struct vionet_dev *dev) +{ + struct tun_capabilities tcap; + + memset(&tcap, 0, sizeof(tcap)); + + if (dev->cfg.guest_feature & VIRTIO_NET_F_GUEST_CSUM) { + tcap.tun_if_capabilities |= IFCAP_CSUM_TCPv4 | IFCAP_CSUM_UDPv4; + tcap.tun_if_capabilities |= IFCAP_CSUM_TCPv6 | IFCAP_CSUM_UDPv6; + } + + if (ioctl(dev->data_fd, TUNSCAP, &tcap) == -1) + fatal("tap(4) TUNSCAP"); +} + +/* * Update the gpa and hva of the virtqueue. */ static void @@ -383,7 +423,9 @@ vionet_rx(struct vionet_dev *dev, int fd struct vring_avail *avail; struct vring_used *used; struct virtio_vq_info *vq_info; + struct virtio_net_hdr *vhp; struct iovec *iov; + struct tun_hdr th; int notify = 0; ssize_t sz; uint8_t status = 0; @@ -414,8 +456,8 @@ vionet_rx(struct vionet_dev *dev, int fd goto reset; } - iov = &iov_rx[0]; - iov_cnt = 1; + iov = &iov_rx[1]; + iov_cnt = 2; /* * First descriptor should be at least as large as the @@ -435,7 +477,7 @@ vionet_rx(struct vionet_dev *dev, int fd iov->iov_base = hvaddr_mem(desc->addr, iov->iov_len); if (iov->iov_base == NULL) goto reset; - memset(iov->iov_base, 0, sizeof(struct virtio_net_hdr)); + vhp = iov->iov_base; /* Tweak the iovec to account for the virtio_net_hdr. */ iov->iov_len -= sizeof(struct virtio_net_hdr); @@ -486,14 +528,19 @@ vionet_rx(struct vionet_dev *dev, int fd */ if (dev->lockedmac || fd != dev->data_fd) sz = vionet_rx_copy(dev, fd, iov_rx, iov_cnt, - chain_len); - else + chain_len, &th); + else { + iov_rx[0].iov_base = &th; + iov_rx[0].iov_len = sizeof(th); sz = vionet_rx_zerocopy(dev, fd, iov_rx, iov_cnt); + } if (sz == -1) goto reset; if (sz == 0) /* No packets, so bail out for now. */ break; + thdr2vhdr(&th, vhp, iov_rx + 1, iov_cnt - 1); + /* * Account for the prefixed header since it wasn't included * in the copy or zerocopy operations. @@ -533,9 +580,9 @@ reset: */ ssize_t vionet_rx_copy(struct vionet_dev *dev, int fd, const struct iovec *iov, - int iov_cnt, size_t chain_len) + int iov_cnt, size_t chain_len, struct tun_hdr *th) { - static uint8_t buf[VIONET_HARD_MTU]; + static uint8_t buf[sizeof(struct tun_hdr) + VIONET_HARD_MTU]; struct packet *pkt = NULL; struct ether_header *eh = NULL; uint8_t *payload = buf; @@ -543,9 +590,10 @@ vionet_rx_copy(struct vionet_dev *dev, i ssize_t sz; /* If reading from the tap(4), try to right-size the read. */ - if (fd == dev->data_fd) - nbytes = MIN(chain_len, VIONET_HARD_MTU); - else if (fd == pipe_inject[READ]) + if (fd == dev->data_fd) { + nbytes = sizeof(struct tun_hdr) + + MIN(chain_len, VIONET_HARD_MTU); + } else if (fd == pipe_inject[READ]) nbytes = sizeof(struct packet); else { log_warnx("%s: invalid fd: %d", __func__, fd); @@ -564,10 +612,20 @@ vionet_rx_copy(struct vionet_dev *dev, i return (-1); } return (0); - } else if (fd == dev->data_fd && sz < VIONET_MIN_TXLEN) { + } else if (fd == dev->data_fd) { + if ((size_t)sz < sizeof(struct tun_hdr)) { + log_warnx("%s: short tun_hdr", __func__); + return (0); + } + memcpy(th, payload, sizeof *th); + payload += sizeof(struct tun_hdr); + sz -= sizeof(struct tun_hdr); + /* If reading the tap(4), we should get valid ethernet. */ - log_warnx("%s: invalid packet size", __func__); - return (0); + if (sz < VIONET_MIN_TXLEN) { + log_warnx("%s: invalid packet size", __func__); + return (0); + } } else if (fd == pipe_inject[READ] && sz != sizeof(struct packet)) { log_warnx("%s: invalid injected packet object (sz=%ld)", __func__, sz); @@ -645,6 +703,13 @@ vionet_rx_zerocopy(struct vionet_dev *de sz = readv(fd, iov, iov_cnt); if (sz == -1 && errno == EAGAIN) return (0); + + if ((size_t)sz < sizeof(struct tun_hdr)) { + log_warnx("%s: short tun_hdr", __func__); + return (0); + } + sz -= sizeof(struct tun_hdr); + return (sz); } @@ -729,6 +794,8 @@ vionet_tx(struct virtio_dev *dev) struct iovec *iov; struct packet pkt; uint8_t status = 0; + struct virtio_net_hdr *vhp; + struct tun_hdr th; status = vionet->cfg.device_status & VIRTIO_CONFIG_DEVICE_STATUS_DRIVER_OK; @@ -756,8 +823,10 @@ vionet_tx(struct virtio_dev *dev) goto reset; } - iov = &iov_tx[0]; - iov_cnt = 0; + /* the 0th slot will by used by the tun_hdr */ + + iov = &iov_tx[1]; + iov_cnt = 1; chain_len = 0; /* @@ -765,18 +834,23 @@ vionet_tx(struct virtio_dev *dev) * descriptor sized to the virtio_net_hdr. However, the framing * is not guaranteed, so check for packet data. */ - iov->iov_len = desc->len; - if (iov->iov_len < sizeof(struct virtio_net_hdr)) { + if (desc->len < sizeof(*vhp)) { log_warnx("%s: invalid descriptor length", __func__); goto reset; - } else if (iov->iov_len > sizeof(struct virtio_net_hdr)) { - /* Chop off the virtio header, leaving packet data. */ - iov->iov_len -= sizeof(struct virtio_net_hdr); - chain_len += iov->iov_len; - iov->iov_base = hvaddr_mem(desc->addr + - sizeof(struct virtio_net_hdr), iov->iov_len); + } + + /* Chop the virtio net header off */ + vhp = hvaddr_mem(desc->addr, sizeof(*vhp)); + if (vhp == NULL) + goto reset; + + iov->iov_len = desc->len - sizeof(*vhp); + if (iov->iov_len > 0) { + iov->iov_base = hvaddr_mem(desc->addr + sizeof(*vhp), + iov->iov_len); if (iov->iov_base == NULL) goto reset; + chain_len += iov->iov_len; iov_cnt++; } @@ -820,7 +894,7 @@ vionet_tx(struct virtio_dev *dev) * descriptor with packet data contains a large enough buffer * for this inspection. */ - iov = &iov_tx[0]; + iov = &iov_tx[1]; if (vionet->lockedmac) { if (iov->iov_len < ETHER_HDR_LEN) { log_warnx("%s: insufficient header data", @@ -846,6 +920,15 @@ vionet_tx(struct virtio_dev *dev) } } + /* + * if we look at more of vhp we might need to copy + * it so it's aligned properly + */ + vhdr2thdr(vhp, &th, iov_tx + 1, iov_cnt - 1); + + iov_tx[0].iov_base = &th; + iov_tx[0].iov_len = sizeof(th); + /* Write our packet to the tap(4). */ sz = writev(vionet->data_fd, iov_tx, iov_cnt); if (sz == -1 && errno != ENOBUFS) { @@ -1064,6 +1147,7 @@ handle_io_write(struct viodev_msg *msg, break; case VIRTIO_CONFIG_GUEST_FEATURES: vionet->cfg.guest_feature = data; + vionet_update_offload(vionet); break; case VIRTIO_CONFIG_QUEUE_PFN: vionet->cfg.queue_pfn = data; @@ -1396,4 +1480,153 @@ vionet_deassert_pic_irq(struct virtio_de &msg, sizeof(msg), ev_base_main); if (ret == -1) log_warnx("%s: failed to assert irq %d", __func__, dev->irq); +} + +static int +memcpyv(void *buf, size_t len, size_t off, const struct iovec *iov, int iovcnt) +{ + uint8_t *dst = buf; + size_t l; + + for (;;) { + if (iovcnt == 0) + return (-1); + + if (off < iov->iov_len) + break; + + off -= iov->iov_len; + iov++; + iovcnt--; + } + + l = off + len; + if (l > iov->iov_len) + l = iov->iov_len; + l -= off; + + memcpy(dst, (const uint8_t *)iov->iov_base + off, l); + dst += l; + len -= l; + + if (len == 0) + return (0); + + for (;;) { + if (iovcnt == 0) + return (-1); + + l = len; + if (l > iov->iov_len) + l = iov->iov_len; + + memcpy(dst, (const uint8_t *)iov->iov_base, l); + dst += l; + len -= l; + + if (len == 0) + break; + + iov++; + iovcnt--; + } + + return (0); +} + +static void +hdr_extract(const struct iovec *iov, int iovcnt, size_t *off, uint8_t *proto) +{ + size_t offs; + uint16_t etype; + + if (memcpyv(&etype, sizeof(etype), + offsetof(struct ether_header, ether_type), + iov, iovcnt) == -1) + return; + + *off = sizeof(struct ether_header); + + if (etype == htons(ETHERTYPE_VLAN)) { + if (memcpyv(&etype, sizeof(etype), + offsetof(struct ether_vlan_header, evl_proto), + iov, iovcnt) == -1) + return; + + *off = sizeof(struct ether_vlan_header); + } + + if (etype == htons(ETHERTYPE_IP)) { + uint16_t len; + + /* Get ipproto field from IP header. */ + offs = *off + offsetof(struct ip, ip_p); + if (memcpyv(proto, sizeof(*proto), offs, iov, iovcnt) == -1) + return; + + /* Get IP length field from IP header. */ + offs = *off + offsetof(struct ip, ip_len); + if (memcpyv(&len, sizeof(len), offs, iov, iovcnt) == -1) + return; + + *off += len; + } else if (etype == htons(ETHERTYPE_IPV6)) { + /* Get next header field from IP header. */ + offs = *off + offsetof(struct ip6_hdr, ip6_nxt); + if (memcpyv(proto, sizeof(*proto), offs, iov, iovcnt) == -1) + return; + + *off += sizeof(struct ip6_hdr); + } +} + +static void +vhdr2thdr(struct virtio_net_hdr *vh, struct tun_hdr *th, + const struct iovec *iov, int iovcnt) +{ + memset(th, 0, sizeof(*th)); + + if (vh->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) { + size_t off; + uint8_t proto; + + hdr_extract(iov, iovcnt, &off, &proto); + + switch (proto) { + case IPPROTO_TCP: + th->th_flags |= TUN_H_TCP_CSUM; + break; + + case IPPROTO_UDP: + th->th_flags |= TUN_H_UDP_CSUM; + break; + } + } +} + +static void +thdr2vhdr(struct tun_hdr *th, struct virtio_net_hdr *vh, + const struct iovec *iov, int iovcnt) +{ + size_t off; + uint8_t proto; + + memset(vh, 0, sizeof(*vh)); + + if (th->th_flags & (TUN_H_TCP_CSUM | TUN_H_UDP_CSUM)) { + hdr_extract(iov, iovcnt, &off, &proto); + + vh->flags |= VIRTIO_NET_HDR_F_NEEDS_CSUM; + vh->csum_start = off; + + switch (proto) { + case IPPROTO_TCP: + vh->csum_offset = offsetof(struct tcphdr, th_sum); + break; + + case IPPROTO_UDP: + vh->csum_offset = offsetof(struct udphdr, uh_sum); + break; + } + } } Index: usr.sbin/vmd/virtio.c =================================================================== RCS file: /cvs/src/usr.sbin/vmd/virtio.c,v diff -u -p -r1.124 virtio.c --- usr.sbin/vmd/virtio.c 12 May 2025 17:17:42 -0000 1.124 +++ usr.sbin/vmd/virtio.c 24 May 2025 02:58:50 -0000 @@ -55,6 +55,8 @@ SLIST_HEAD(virtio_dev_head, virtio_dev) #define MAXPHYS (64 * 1024) /* max raw I/O transfer size */ +#define VIRTIO_NET_F_CSUM (1<<0) +#define VIRTIO_NET_F_GUEST_CSUM (1<<1) #define VIRTIO_NET_F_MAC (1<<5) #define VMMCI_F_TIMESYNC (1<<0) @@ -622,6 +624,10 @@ virtio_init(struct vmd_vm *vm, int child /* MAC address has been assigned by the parent */ memcpy(&dev->vionet.mac, &vmc->vmc_macs[i], 6); dev->vionet.cfg.device_feature = VIRTIO_NET_F_MAC; + + /* offload checksum to the kernel */ + dev->vionet.cfg.device_feature = VIRTIO_NET_F_CSUM; + dev->vionet.cfg.device_feature |= VIRTIO_NET_F_GUEST_CSUM; dev->vionet.lockedmac = vmc->vmc_ifflags[i] & VMIFF_LOCKED ? 1 : 0; Index: usr.sbin/vmd/virtio.h =================================================================== RCS file: /cvs/src/usr.sbin/vmd/virtio.h,v diff -u -p -r1.54 virtio.h --- usr.sbin/vmd/virtio.h 12 May 2025 17:17:42 -0000 1.54 +++ usr.sbin/vmd/virtio.h 24 May 2025 02:58:51 -0000 @@ -307,6 +307,9 @@ struct virtio_net_hdr { /* uint16_t num_buffers; */ }; +#define VIRTIO_NET_HDR_F_NEEDS_CSUM 1 /* flags */ +#define VIRTIO_NET_HDR_F_DATA_VALID 2 /* flags */ + enum vmmci_cmd { VMMCI_NONE = 0, VMMCI_SHUTDOWN,