Re: [PATCH] common/mlx5: fix misalignment issue detected by ASan

[Raslan Darawsheh <rasland@nvidia.com>]

Hi,

From: Shani Peretz <shperetz@nvidia.com>
Sent: Tuesday, November 12, 2024 10:21 AM
To: dev@dpdk.org
Cc: Shani Peretz; Maayan Kashani; Raslan Darawsheh; Suanming Mou; Bing Zhao; Dariusz Sosnowski; Slava Ovsiienko; Ori Kam; Matan Azrad
Subject: [PATCH] common/mlx5: fix misalignment issue detected by ASan

ASan reported a runtime error due to misalignment
involving three structures.

The first issue arises when accessing
l_inconst->cache[MLX5_LIST_GLOBAL]->h.
If struct mlx5_list_cache is not properly aligned, the pointer gc,
assigned to l_inconst->cache[MLX5_LIST_GLOBAL], could be misaligned.
To address this, the __rte_aligned(16) attribute was added to
struct mlx5_list_inconst in struct mlx5_list, which includes struct
mlx5_list_cache, ensuring that the entire mlx5_list structure,
including mlx5_list_cache, is aligned to 64 bytes.

To resolve misalignment issues with struct mlx5_flow_handle,
The initialization of resources for the ipool ensures that
the ipool size is rounded up to the 8-byte boundary

The error in assigning values to actions[i] was due to potential
padding or misalignment in struct mlx5_modification_cmd.
To prevent such issues, the __rte_packed attribute was added to
struct mlx5_modification_cmd, ensuring that the structure is packed
without extra padding which helps avoid misaligned memory accesses.

Two performance degradation tests were conducted.
Following are the results comparing this commit to the most recent
commit in mlnx_dpdk_22.11 at that time (b69408ae453).

Before asan misalignment fix (average kflows/sec) -
Insertion - 4461.269, Deletion - 7799.9992
After:
Insertion - 4579.0642 , Deletion - 7913.0034

Fixes: 9a4c36880704 ("common/mlx5: optimize cache list object memory")
Cc: suanmingm@nvidia.com

Signed-off-by: Shani Peretz <shperetz@nvidia.com>
Acked-by: Bing Zhao <bingz@nvidia.com>

Patch applied to next-net-mlx,

Kindest regards,
Raslan Darawsheh