tmfifo: Fix a memory barrier issue

[Liming Sun]

This one is used to track a code merge of the tmfifo driver.

SRU Justification:

[Impact]
* The virtio framework uses wmb() when updating avail->idx. It guarantees the write order, but not necessarily loading order for the code accessing the memory. So potentially it could cause traffic stuck which has been observed in the field.

[Fix]
* This commit adds a load barrier after reading the avail->idx to make sure all the data in the descriptor is visible. It also adds a barrier when returning the packet to virtio framework to make sure read/writes are visible to the virtio code.

[Test Case]
* Just normal test. This change doesn't affect any functionality.

[Regression Potential]
* SQA team has been running test with this fix for quite some time (several months). No issue as observed.

[Other]
* N/A

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This bug is awaiting verification that the kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed-focal' to 'verification-done-focal'. If the problem still exists, change the tag 'verification-needed-focal' to 'verification-failed-focal'.

If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed.

See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you!

[Launchpad Janitor (janitor)]

This bug was fixed in the package linux-bluefield - 5.4.0-1012.15

---------------
linux-bluefield (5.4.0-1012.15) focal; urgency=medium

  * focal/linux-bluefield: 5.4.0-1012.15 -proposed tracker (LP: #1927599)

  * Focal update: v5.4.109 upstream stable release (LP: #1923220)
    - [Config] bluefield: Record PNFS_FLEXFILE_LAYOUT=y

  * mlx-bootctl: rshim logging display from linux sysfs (LP: #1927263)
    - mlx-bootctl: rshim logging display from linux sysfs

  * Backport TLS Bond (LP: #1926994)
    - netpoll: Fix use correct return type for ndo_start_xmit()
    - netpoll: remove dev argument from netpoll_send_skb_on_dev()
    - netpoll: move netpoll_send_skb() out of line
    - netpoll: netpoll_send_skb() returns transmit status
    - netpoll: accept NULL np argument in netpoll_send_skb()
    - bonding: propagate transmit status
    - xfrm: bail early on slave pass over skb
    - ixgbe_ipsec: become aware of when running as a bonding slave
    - mlx5: become aware of when running as a bonding slave
    - bonding: support hardware encryption offload to slaves
    - bonding: Remove extraneous parentheses in bond_setup
    - bonding: allow xfrm offload setup post-module-load
    - bonding/xfrm: use real_dev instead of slave_dev
    - bonding: deal with xfrm state in all modes and add more error-checking
    - bonding: fix feature flag setting at init time
    - net/core: Introduce netdev_get_xmit_slave
    - bonding: Export skip slave logic to function
    - bonding: Rename slave_arr to usable_slaves
    - bonding/alb: Add helper functions to get the xmit slave
    - bonding: Add helper function to get the xmit slave based on hash
    - bonding: Add helper function to get the xmit slave in rr mode
    - bonding: Add function to get the xmit slave in active-backup mode
    - bonding: Add array of all slaves
    - bonding: Implement ndo_get_xmit_slave
    - net: netdevice: Add operation ndo_sk_get_lower_dev
    - net/bonding: Take IP hash logic into a helper
    - net/bonding: Implement ndo_sk_get_lower_dev
    - net/bonding: Take update_features call out of XFRM funciton
    - net/bonding: Implement TLS TX device offload
    - net/bonding: Declare TLS RX device offload support
    - net/tls: Device offload to use lowest netdevice in chain
    - net/tls: Except bond interface from some TLS checks

  * Do offload refresh when requested (LP: #1927374)
    - SAUCE: netfilter: flowtable: Do flow offload refresh when requested

  * To support reclassifying a packet more than 4 times need to increase the
    reclassification setting. (LP: #1927257)
    - SAUCE: net/sched: Increase support of reclassification to 15

  * Enable CONFIG_IPV6_MROUTE_MULTIPLE_TABLES in kernel configuration
    (LP: #1927142)
    - [Config] CONFIG_IPV6_MROUTE_MULTIPLE_TABLES=y

  * Enable CONFIG_NET_VRF in kernel configuration (LP: #1923620)
    - [Config] CONFIG_NET_VRF=m

  * Fix NAT IPv6 offload mangling (LP: #1927244)
    - netfilter: flowtable: fix NAT IPv6 offload mangling

  * mlxbf-tmfifo: Add ctrl message and MAC configuration (LP: #1927253)
    - SAUCE: platform/mellanox: Add ctrl message and MAC configuration

  * tmfifo: Fix a memory barrier issue (LP: #1927262)...