Re: [PATCH net 1/4] net/mlx5e: Fix HV VHCA stats zero-sized buffer allocation

[Jacob Keller <jacob.e.keller@intel.com>]

On 6/4/2026 6:50 AM, Tariq Toukan wrote:
> From: Feng Liu <feliu@nvidia.com>
> 
> mlx5e_hv_vhca_stats_create() is called from mlx5e_nic_enable(),
> before mlx5e_open(). At that point priv->stats_nch is still zero,
> because it is only ever incremented in mlx5e_channel_stats_alloc(),
> which is reached only from mlx5e_open_channel().
> 
> mlx5e_hv_vhca_stats_buf_size() therefore returns 0, and
> kvzalloc(0, GFP_KERNEL) returns ZERO_SIZE_PTR ((void *)16) rather
> than NULL. The "if (!buf)" guard does not catch this, and
> mlx5e_hv_vhca_stats_create() completes "successfully" with
> priv->stats_agent.buf set to ZERO_SIZE_PTR.
> 
> Once channels are opened (priv->stats_nch > 0) and the hypervisor
> enables stats reporting, mlx5e_hv_vhca_stats_work() recomputes
> buf_len using the new non-zero stats_nch and calls
> memset(buf, 0, buf_len) on ZERO_SIZE_PTR, faulting at address 0x10.
> 
> Allocate the buffer based on priv->max_nch, which is set in
> mlx5e_priv_init() and is the upper bound on stats_nch:
> 
>   - Add a separate helper mlx5e_hv_vhca_stats_buf_max_size() that
>     returns sizeof(per_ring_stats) * max(max_nch, stats_nch), and
>     use it for the kvzalloc() in mlx5e_hv_vhca_stats_create().
>   - Keep mlx5e_hv_vhca_stats_buf_size() (which returns based on
>     stats_nch) for the worker's active payload size, so the wire
>     format (block->rings = stats_nch) and the amount of data filled
>     by mlx5e_hv_vhca_fill_stats() are unchanged.
> 
> The max(max_nch, stats_nch) guard handles the rare case where
> mlx5e_attach_netdev() recomputes max_nch downward across a
> detach/resume cycle while priv->stats_nch persists (mlx5e_detach_netdev
> does not call mlx5e_priv_cleanup, so stats_nch is only reset when
> the netdev is destroyed). Without the guard, the worker could compute
> buf_len from stats_nch and overrun the smaller buffer allocated based
> on the reduced max_nch.
> 
> This mirrors the existing mlx5e pattern of preallocating arrays of
> size max_nch (e.g. priv->channel_stats) and lazily populating
> entries up to stats_nch on demand.
> 
> Fixes: fa691d0c9c08 ("net/mlx5e: Allocate per-channel stats dynamically at first usage")
> Signed-off-by: Feng Liu <feliu@nvidia.com>
> Reviewed-by: Eran Ben Elisha <eranbe@nvidia.com>
> Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
> ---

Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>