Add read memory barrier to ensure the order of operations when accessing
control queue descriptors. Specifically, we want to avoid cases where loads
can be reordered:
1. Load #1 is dispatched to read descriptor flags.
2. Load #2 is dispatched to read some other field from the descriptor.
3. Load #2 completes, accessing memory/cache at a point in time when the DD
flag is zero.
4. NIC DMA overwrites the descriptor, now the DD flag is one.
5. Any fields loaded before step 4 are now inconsistent with the actual
descriptor state.
Add read memory barrier between steps 1 and 2, so that load #2 is not
executed until load #1 has completed.
Fixes: 8077c727561a ("idpf: add controlq init and reset checks")
Reviewed-by: Przemek Kitszel <przemyslaw.kits...@intel.com>
Reviewed-by: Sridhar Samudrala <sridhar.samudr...@intel.com>
Suggested-by: Lance Richardson <rla...@google.com>
Signed-off-by: Emil Tantilov <emil.s.tanti...@intel.com>
---
Changelog
v2:
- Rewrote comment to fit on a single line
- Added new line as separator
- Updated last sentence in commit message to include load #
v1:
https://lore.kernel.org/intel-wired-lan/20241115021618.20565-1-emil.s.tanti...@intel.com/
---
drivers/net/ethernet/intel/idpf/idpf_controlq.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/drivers/net/ethernet/intel/idpf/idpf_controlq.c
b/drivers/net/ethernet/intel/idpf/idpf_controlq.c
index 4849590a5591..b28991dd1870 100644
--- a/drivers/net/ethernet/intel/idpf/idpf_controlq.c
+++ b/drivers/net/ethernet/intel/idpf/idpf_controlq.c
@@ -376,6 +376,9 @@ int idpf_ctlq_clean_sq(struct idpf_ctlq_info *cq, u16
*clean_count,
if (!(le16_to_cpu(desc->flags) & IDPF_CTLQ_FLAG_DD))
break;
+ /* Ensure no other fields are read until DD flag is checked */
+ dma_rmb();
+
/* strip off FW internal code */
desc_err = le16_to_cpu(desc->ret_val) & 0xff;
@@ -563,6 +566,9 @@ int idpf_ctlq_recv(struct idpf_ctlq_info *cq, u16
*num_q_msg,
if (!(flags & IDPF_CTLQ_FLAG_DD))
break;
+ /* Ensure no other fields are read until DD flag is checked */
+ dma_rmb();
+
q_msg[i].vmvf_type = (flags &
(IDPF_CTLQ_FLAG_FTYPE_VM |
IDPF_CTLQ_FLAG_FTYPE_PF)) >>
--
2.17.2
