On Sun, Oct 18, 2026 at 11:21 AM Morten Brørup <[email protected]> wrote: > > There is a special rule for UDP, where a checksum of zero is as 0xffff > instead of zero. > > Identifying packet types requires masking with the mask, not the value, > before comparing to the value. > Identifying by masking with the L4 UDP packet type value (0x00000200) > instead of the L4 packet type mask caused other L4 packet types to match; > specifically IP fragments, IGMP packets, and certain non-fragments. > This meant that some non-UDP packets followed the special UDP checksum > rule, which they should not. > > Updated to mask the packet type with the L4 packet type mask and then > compare to the L4 UDP packet type value, so only UDP packets follow the > special UDP checksum rule. > > Furthermore, according to the mbuf documentation, Tx checksum offload > requires that "ol_flags" is set, and only mentions "packet_type" for Rx, > so use "ol_flags" instead of "packet_type" for checking the packet type > at Tx. > > Furthermore, writing the checksum needs room for 2 bytes, not 1 byte. > > Note: > Using "if (unlikely(cksum == 0) && PTYPE_MATCH)" to advise the optimizer > about the need to evaluate PTYPE_MATCH being unlikely. > The probability of cksum being zero is only 1/65536, so it's better to > branch early. > > Fixes: 8ba1723783b2 ("net/vhost: perform SW checksum in Tx path") > Fixes: 8f1750f42e2d ("net/vhost: perform SW checksum in Rx path") > Cc: [email protected] > > Signed-off-by: Morten Brørup <[email protected]> > --- > v3: > * Writing the checksum needs room for 2 bytes, not 1 byte. > v2: > * Use ol_flags instead of packet_type for Tx. > * Added note about the use of unlikely(). > --- > drivers/net/vhost/rte_eth_vhost.c | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) >
Thanks for the fix, it looks good to me: Reviewed-by; Maxime Coquelin <[email protected]> Maxime
