On 11/05, Mina Almasry wrote:
> For device memory TCP, we expect the skb headers to be available in host
> memory for access, and we expect the skb frags to be in device memory
> and unaccessible to the host. We expect there to be no mixing and
> matching of device memory frags (unaccessible) with host memory frags
> (accessible) in the same skb.
>
> Add a skb->devmem flag which indicates whether the frags in this skb
> are device memory frags or not.
>
> __skb_fill_page_desc() now checks frags added to skbs for page_pool_iovs,
> and marks the skb as skb->devmem accordingly.
>
> Add checks through the network stack to avoid accessing the frags of
> devmem skbs and avoid coalescing devmem skbs with non devmem skbs.
>
> Signed-off-by: Willem de Bruijn <willemb@xxxxxxxxxx>
> Signed-off-by: Kaiyuan Zhang <kaiyuanz@xxxxxxxxxx>
> Signed-off-by: Mina Almasry <almasrymina@xxxxxxxxxx>
>
> ---
> include/linux/skbuff.h | 14 +++++++-
> include/net/tcp.h | 5 +--
> net/core/datagram.c | 6 ++++
> net/core/gro.c | 5 ++-
> net/core/skbuff.c | 77 ++++++++++++++++++++++++++++++++++++------
> net/ipv4/tcp.c | 6 ++++
> net/ipv4/tcp_input.c | 13 +++++--
> net/ipv4/tcp_output.c | 5 ++-
> net/packet/af_packet.c | 4 +--
> 9 files changed, 115 insertions(+), 20 deletions(-)
>
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 1fae276c1353..8fb468ff8115 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -805,6 +805,8 @@ typedef unsigned char *sk_buff_data_t;
> * @csum_level: indicates the number of consecutive checksums found in
> * the packet minus one that have been verified as
> * CHECKSUM_UNNECESSARY (max 3)
> + * @devmem: indicates that all the fragments in this skb are backed by
> + * device memory.
> * @dst_pending_confirm: need to confirm neighbour
> * @decrypted: Decrypted SKB
> * @slow_gro: state present at GRO time, slower prepare step required
> @@ -991,7 +993,7 @@ struct sk_buff {
> #if IS_ENABLED(CONFIG_IP_SCTP)
> __u8 csum_not_inet:1;
> #endif
> -
> + __u8 devmem:1;
> #if defined(CONFIG_NET_SCHED) || defined(CONFIG_NET_XGRESS)
> __u16 tc_index; /* traffic control index */
> #endif
> @@ -1766,6 +1768,12 @@ static inline void skb_zcopy_downgrade_managed(struct sk_buff *skb)
> __skb_zcopy_downgrade_managed(skb);
> }
>
> +/* Return true if frags in this skb are not readable by the host. */
> +static inline bool skb_frags_not_readable(const struct sk_buff *skb)
> +{
> + return skb->devmem;
bikeshedding: should we also rename 'devmem' sk_buff flag to 'not_readable'?
It better communicates the fact that the stack shouldn't dereference the
frags (because it has 'devmem' fragments or for some other potential
future reason).
