git: c1fa70c6e9f6 - main - vtnet: offer VIRTIO_NET_F_GUEST_CSUM
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Date: Mon, 14 Sep 2026 20:17:25 UTC
The branch main has been updated by tuexen:
URL: https://cgit.FreeBSD.org/src/commit/?id=c1fa70c6e9f652e79ef3ffaf366949744f11ce5c
commit c1fa70c6e9f652e79ef3ffaf366949744f11ce5c
Author: Timo Völker <timo.voelker@fh-muenster.de>
AuthorDate: 2026-09-14 20:09:35 +0000
Commit: Michael Tuexen <tuexen@FreeBSD.org>
CommitDate: 2026-09-14 20:16:25 +0000
vtnet: offer VIRTIO_NET_F_GUEST_CSUM
Always offer the VIRTIO_NET_F_GUEST_CSUM feature to the host, and not
only if RXCSUM is enabled on vtnet. Instead of using RXCSUM to control
whether this feature will be negotiated with the host, just use it to
control whether the VIRTIO_NET_HDR_F_DATA_VALID flag on an incoming
packet is processed (i.e., translated to the corresponding mbuf flag
only if RXCSUM is enabled on the vtnet interface).
This has two benefits:
1. Enabling/disabling RXCSUM on vtnet does not require feature
renegotiation.
2. The host is always allowed to send locally generated TCP or UDP
packets to the guest without computing a full checksum (by setting
the VIRTIO_NET_HDR_F_NEEDS_CSUM flag) and not only if the guest has
enabled RXCSUM on vtnet. Since locally generated packets do not
require a checksum, this saves otherwise unnecessarily wasted
computing power.
If a user of a FreeBSD guest really does not want to negotiate the
VIRTIO_NET_F_GUEST_CSUM feature with the host, it still can disable
the loader tunable hw.vtnet.csum_disable.
Reviewed by: kfv, tuexen
MFC after: 1 week
MFC to: stable/15
Differential Revision: https://reviews.freebsd.org/D59052
---
sys/dev/virtio/network/if_vtnet.c | 87 ++++++++++++++++++---------------------
1 file changed, 41 insertions(+), 46 deletions(-)
diff --git a/sys/dev/virtio/network/if_vtnet.c b/sys/dev/virtio/network/if_vtnet.c
index 53f5bba146fc..15dd50e7df77 100644
--- a/sys/dev/virtio/network/if_vtnet.c
+++ b/sys/dev/virtio/network/if_vtnet.c
@@ -1456,11 +1456,12 @@ static int
vtnet_ioctl_ifcap(struct vtnet_softc *sc, struct ifreq *ifr)
{
if_t ifp;
- int mask, reinit, update;
+ int mask;
+ bool reinit, update;
ifp = sc->vtnet_ifp;
mask = (ifr->ifr_reqcap & if_getcapabilities(ifp)) ^ if_getcapenable(ifp);
- reinit = update = 0;
+ reinit = update = false;
VTNET_CORE_LOCK_ASSERT(sc);
@@ -1500,52 +1501,44 @@ vtnet_ioctl_ifcap(struct vtnet_softc *sc, struct ifreq *ifr)
if_togglehwassist(ifp, CSUM_IP6_TSO);
}
}
-
- if (mask & (IFCAP_RXCSUM | IFCAP_RXCSUM_IPV6 | IFCAP_LRO)) {
- /*
- * These Rx features require the negotiated features to
- * be updated. Avoid a full reinit if possible.
- */
- if (sc->vtnet_features & VIRTIO_NET_F_CTRL_GUEST_OFFLOADS)
- update = 1;
- else
- reinit = 1;
-
- /* BMV: Avoid needless renegotiation for just software LRO. */
- if ((mask & (IFCAP_RXCSUM | IFCAP_RXCSUM_IPV6 | IFCAP_LRO)) ==
- IFCAP_LRO && vtnet_software_lro(sc))
- reinit = update = 0;
- /*
- * VirtIO does not distinguish between receive checksum offload
- * for IPv4 and IPv6 packets, so treat them as a pair.
- */
- if (mask & (IFCAP_RXCSUM | IFCAP_RXCSUM_IPV6)) {
- if_togglecapenable(ifp, IFCAP_RXCSUM);
- if_togglecapenable(ifp, IFCAP_RXCSUM_IPV6);
+ /*
+ * VirtIO does not distinguish between receive checksum offload
+ * for IPv4 and IPv6 packets, so treat them as a pair.
+ */
+ if (mask & (IFCAP_RXCSUM | IFCAP_RXCSUM_IPV6)) {
+ if (if_getcapenable(ifp) & IFCAP_RXCSUM &&
+ if_getcapenable(ifp) & IFCAP_LRO) {
+ /* Disable lro, because rxcsum will be disabled. */
+ if_setcapenablebit(ifp, 0, IFCAP_LRO);
+ /* Changing hardware LRO requires an update. */
+ update = !vtnet_software_lro(sc);
+ mask &= ~IFCAP_LRO;
}
- if (mask & IFCAP_LRO)
+ if_togglecapenable(ifp, IFCAP_RXCSUM);
+ if_togglecapenable(ifp, IFCAP_RXCSUM_IPV6);
+ }
+ if (mask & IFCAP_LRO) {
+ if (if_getcapenable(ifp) & (IFCAP_RXCSUM | IFCAP_LRO)) {
if_togglecapenable(ifp, IFCAP_LRO);
- /* Both SW and HW TCP LRO require receive checksum offload. */
- if ((if_getcapenable(ifp) &
- (IFCAP_RXCSUM | IFCAP_RXCSUM_IPV6)) == 0)
- if_setcapenablebit(ifp, 0, IFCAP_LRO);
+ /* Changing hardware LRO requires an update. */
+ update = !vtnet_software_lro(sc);
+ }
}
-
if (mask & IFCAP_VLAN_HWFILTER) {
- /* These Rx features require renegotiation. */
- reinit = 1;
+ /* This Rx feature requires renegotiation. */
+ reinit = true;
if (mask & IFCAP_VLAN_HWFILTER)
if_togglecapenable(ifp, IFCAP_VLAN_HWFILTER);
}
-
if (mask & IFCAP_VLAN_HWTSO)
if_togglecapenable(ifp, IFCAP_VLAN_HWTSO);
if (mask & IFCAP_VLAN_HWTAGGING)
if_togglecapenable(ifp, IFCAP_VLAN_HWTAGGING);
if (if_getdrvflags(ifp) & IFF_DRV_RUNNING) {
- if (reinit) {
+ if (reinit || (update && (sc->vtnet_features &
+ VIRTIO_NET_F_CTRL_GUEST_OFFLOADS) == 0)) {
if_setdrvflagbits(ifp, 0, IFF_DRV_RUNNING);
vtnet_init_locked(sc, 0);
} else if (update)
@@ -2084,8 +2077,20 @@ vtnet_rxq_input(struct vtnet_rxq *rxq, struct mbuf *m,
M_HASHTYPE_SET(m, M_HASHTYPE_OPAQUE);
}
- if (hdr->flags &
- (VIRTIO_NET_HDR_F_NEEDS_CSUM | VIRTIO_NET_HDR_F_DATA_VALID)) {
+ /*
+ * Check if VirtIO header flags are set that need to be translated to
+ * mbuf flags.
+ *
+ * Translate VIRTIO_NET_HDR_F_DATA_VALID flag only if IFCAP_RXCSUM is
+ * enabled. If it is disabled, meaning the user does not want to use the
+ * result of a previous validation, this flag is ignored.
+ *
+ * Note that IFCAP_RXCSUM and IFCAP_RXCSUM_IPV6 are treated as pair:
+ * Either both are enabled, or neither of them is.
+ */
+ if ((hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) ||
+ ((hdr->flags & VIRTIO_NET_HDR_F_DATA_VALID) &&
+ (if_getcapenable(ifp) & IFCAP_RXCSUM))) {
#if defined(INET) || defined(INET6)
int ret;
@@ -3318,9 +3323,6 @@ vtnet_virtio_reinit(struct vtnet_softc *sc)
* via if_capenable and if_hwassist.
*/
- if ((if_getcapenable(ifp) & (IFCAP_RXCSUM | IFCAP_RXCSUM_IPV6)) == 0)
- features &= ~(VIRTIO_NET_F_GUEST_CSUM | VTNET_LRO_FEATURES);
-
if ((if_getcapenable(ifp) & IFCAP_LRO) == 0)
features &= ~VTNET_LRO_FEATURES;
@@ -3465,13 +3467,6 @@ vtnet_update_rx_offloads(struct vtnet_softc *sc)
VTNET_CORE_LOCK_ASSERT(sc);
- if (if_getcapabilities(ifp) & (IFCAP_RXCSUM | IFCAP_RXCSUM_IPV6)) {
- if (if_getcapenable(ifp) & (IFCAP_RXCSUM | IFCAP_RXCSUM_IPV6))
- features |= VIRTIO_NET_F_GUEST_CSUM;
- else
- features &= ~VIRTIO_NET_F_GUEST_CSUM;
- }
-
if (if_getcapabilities(ifp) & IFCAP_LRO && !vtnet_software_lro(sc)) {
if (if_getcapenable(ifp) & IFCAP_LRO)
features |= VTNET_LRO_FEATURES;