i40e: support generic devlink param "max_mac_per_vf"

Currently the i40e driver enforces its own internally calculated per-VF MAC
filter limit, derived from the number of allocated VFs and available
hardware resources. This limit is not configurable by the administrator,
which makes it difficult to control how many MAC addresses each VF may
use.

This patch adds support for the new generic devlink runtime parameter
"max_mac_per_vf" which provides administrators with a way to cap the
number of MAC addresses a VF can use:

- When the parameter is set to 0 (default), the driver continues to use
  its internally calculated limit.

- When set to a non-zero value, the driver applies this value as a strict
  cap for VFs, overriding the internal calculation.

Important notes:

- The configured value is a theoretical maximum. Hardware limits may
  still prevent additional MAC addresses from being added, even if the
  parameter allows it.

- Since MAC filters are a shared hardware resource across all VFs,
  setting a high value may cause resource contention and starve other
  VFs.

- This change gives administrators predictable and flexible control over
  VF resource allocation, while still respecting hardware limitations.

- Previous discussion about this change:
  https://lore.kernel.org/netdev/20250805134042.2604897-2-dhill@redhat.com
  https://lore.kernel.org/netdev/20250823094952.182181-1-mheib@redhat.com

Signed-off-by: Mohammad Heib <mheib@redhat.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Tested-by: Rafal Romanowski <rafal.romanowski@intel.com>
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

1 files changed, 23 insertions, 8 deletions

diff --git a/drivers/net/ethernet/intel/i40e/i40e_virtchnl_pf.c b/drivers/net/ethernet/intel/i40e/i40e_virtchnl_pf.c
index 0fe0d52c796b..9d91a382612d 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_virtchnl_pf.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_virtchnl_pf.c
@@ -2935,33 +2935,48 @@ static inline int i40e_check_vf_permission(struct i40e_vf *vf,
 		if (!f)
 			++mac_add_cnt;
 	}
-
-	/* If this VF is not privileged, then we can't add more than a limited
-	 * number of addresses.
+	/* Determine the maximum number of MAC addresses this VF may use.
+	 *
+	 * - For untrusted VFs: use a fixed small limit.
+	 *
+	 * - For trusted VFs: limit is calculated by dividing total MAC
+	 *  filter pool across all VFs/ports.
 	 *
-	 * If this VF is trusted, it can use more resources than untrusted.
-	 * However to ensure that every trusted VF has appropriate number of
-	 * resources, divide whole pool of resources per port and then across
-	 * all VFs.
+	 * - User can override this by devlink param "max_mac_per_vf".
+	 *   If set its value is used as a strict cap for both trusted and
+	 *   untrusted VFs.
+	 *   Note:
+	 *    even when overridden, this is a theoretical maximum; hardware
+	 *    may reject additional MACs if the absolute HW limit is reached.
 	 */
 	if (!vf_trusted)
 		mac_add_max = I40E_VC_MAX_MAC_ADDR_PER_VF;
 	else
 		mac_add_max = I40E_VC_MAX_MACVLAN_PER_TRUSTED_VF(pf->num_alloc_vfs, hw->num_ports);
 
+	if (pf->max_mac_per_vf > 0)
+		mac_add_max = pf->max_mac_per_vf;
+
 	/* VF can replace all its filters in one step, in this case mac_add_max
 	 * will be added as active and another mac_add_max will be in
 	 * a to-be-removed state. Account for that.
 	 */
 	if ((i40e_count_active_filters(vsi) + mac_add_cnt) > mac_add_max ||
 	    (i40e_count_all_filters(vsi) + mac_add_cnt) > 2 * mac_add_max) {
+		if (pf->max_mac_per_vf == mac_add_max && mac_add_max > 0) {
+			dev_err(&pf->pdev->dev,
+				"Cannot add more MAC addresses: VF reached its maximum allowed limit (%d)\n",
+				mac_add_max);
+				return -EPERM;
+		}
 		if (!vf_trusted) {
 			dev_err(&pf->pdev->dev,
 				"Cannot add more MAC addresses, VF is not trusted, switch the VF to trusted to add more functionality\n");
 			return -EPERM;
 		} else {
 			dev_err(&pf->pdev->dev,
-				"Cannot add more MAC addresses, trusted VF exhausted it's resources\n");
+				"Cannot add more MAC addresses: trusted VF reached its maximum allowed limit (%d)\n",
+				mac_add_max);
 			return -EPERM;
 		}
 	}