Apologies... this patch is incomplete so please ignore. I will resubmit a complete patch shortly.
-John- On Thu, May 7, 2026 at 11:12 AM John Ousterhout <[email protected]> wrote: > Consider the following sequence of events: > * The bottom half of a buffer page is filled with data from > packet A. The page has a net reference count (reference count > - bias) of 1. The page is returned to the NIC, flipped to > use the top half. > * Before the reference on the page is released, the NIC returns > the page with no data in it ('size' is zero in ice_clean_rx_irq). > In this case the bias does not get decremented. The page still > has a net reference count of 1, so it gets returned to the NIC. > However, ice_put_rx_mbuf flipped the page so that the bottom > half is active. > * If the NIC stores another packet in the page before packet A > has released its reference, the data in packet A will be > overwritten with data from the new packet. > The fix is for ice_put_rx_mbuf not to flip pages that have a > size of 0. > > Note: major revisions to the ice driver make this patch irrelevant > for recent versions. It applies to longterm stable versions > 6.18.27 and 6.12.86; it also seems relevant for 6.6.137, but would > need modifications for that version. I have not examined earlier > versions > > Signed-off-by: John Ousterhout <[email protected]> > --- > drivers/net/ethernet/intel/ice/ice_txrx.c | 19 ++++++++++++++++--- > 1 file changed, 16 insertions(+), 3 deletions(-) > > diff --git a/drivers/net/ethernet/intel/ice/ice_txrx.c > b/drivers/net/ethernet/intel/ice/ice_txrx.c > index 51c459a3e722..371e6db3c272 100644 > --- a/drivers/net/ethernet/intel/ice/ice_txrx.c > +++ b/drivers/net/ethernet/intel/ice/ice_txrx.c > @@ -1215,6 +1215,9 @@ static void ice_put_rx_mbuf(struct ice_rx_ring > *rx_ring, struct xdp_buff *xdp, > xdp_frags = xdp_get_shared_info_from_buff(xdp)->nr_frags; > > while (idx != ntc) { > + union ice_32b_rx_flex_desc *rx_desc; > + unsigned int size; > + > buf = &rx_ring->rx_buf[idx]; > if (++idx == cnt) > idx = 0; > @@ -1224,10 +1227,20 @@ static void ice_put_rx_mbuf(struct ice_rx_ring > *rx_ring, struct xdp_buff *xdp, > * To do this, only adjust pagecnt_bias for fragments up to > * the total remaining after the XDP program has run. > */ > - if (verdict != ICE_XDP_CONSUMED) > - ice_rx_buf_adjust_pg_offset(buf, xdp->frame_sz); > - else if (i++ <= xdp_frags) > + if (verdict != ICE_XDP_CONSUMED) { > + /* Don't "flip" the page if size is 0: in this case > + * the data in the current half will not be used so > + * it's OK to reuse that half. And, since the bias > + * didn't get decremented for this half, the page > can > + * be returned to the NIC even if the other half is > + * still in use, so flipping the page could cause > + * live packet data to be overwritten. > + */ > + if (size != 0) > + ice_rx_buf_adjust_pg_offset(buf, > xdp->frame_sz); > + } else if (i++ <= xdp_frags) { > buf->pagecnt_bias++; > + } > > ice_put_rx_buf(rx_ring, buf); > } > -- > 2.43.0 > >
