[PATCH v2 net-next 1/5] net: dsa: mv88e6xxx: Improve isolation of standalone ports

[PATCH v2 net-next 1/5] net: dsa: mv88e6xxx: Improve isolation of standalone ports

[Tobias Waldekranz]

Clear MapDA on standalone ports to bypass any ATU lookup that might
point the packet in the wrong direction. This means that all packets
are flooded using the PVT config. So make sure that standalone ports
are only allowed to communicate with the local upstream port.

Here is a scenario in which this is needed:

   CPU
    |     .----.
.---0---. | .--0--.
|  sw0  | | | sw1 |
'-1-2-3-' | '-1-2-'
      '---'

- sw0p1 and sw1p1 are bridged
- sw0p2 and sw1p2 are in standalone mode
- Learning must be enabled on sw0p3 in order for hardware forwarding
  to work properly between bridged ports

1. A packet with SA :aa comes in on sw1p2
   1a. Egresses sw1p0
   1b. Ingresses sw0p3, ATU adds an entry for :aa towards port 3
   1c. Egresses sw0p0

2. A packet with DA :aa comes in on sw0p2
   2a. If an ATU lookup is done at this point, the packet will be
       incorrectly forwarded towards sw0p3. With this change in place,
       the ATU is bypassed and the packet is forwarded in accordance
       with the PVT, which only contains the CPU port.

Signed-off-by: Tobias Waldekranz <tobias@waldekranz.com>
---
 drivers/net/dsa/mv88e6xxx/chip.c | 32 +++++++++++++++++++++++++-------
 drivers/net/dsa/mv88e6xxx/port.c |  7 +++++--
 drivers/net/dsa/mv88e6xxx/port.h |  2 +-
 include/net/dsa.h                | 12 ++++++++++++
 4 files changed, 43 insertions(+), 10 deletions(-)

diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
index 1023e4549359..7f02ec502e71 100644
--- a/drivers/net/dsa/mv88e6xxx/chip.c
+++ b/drivers/net/dsa/mv88e6xxx/chip.c
@@ -1290,8 +1290,15 @@ static u16 mv88e6xxx_port_vlan(struct mv88e6xxx_chip *chip, int dev, int port)
 
 	pvlan = 0;
 
-	/* Frames from user ports can egress any local DSA links and CPU ports,
-	 * as well as any local member of their bridge group.
+	/* Frames from standalone user ports can only egress on the
+	 * upstream port.
+	 */
+	if (!dsa_port_bridge_dev_get(dp))
+		return BIT(dsa_switch_upstream_port(ds));
+
+	/* Frames from bridged user ports can egress any local DSA
+	 * links and CPU ports, as well as any local member of their
+	 * bridge group.
 	 */
 	dsa_switch_for_each_port(other_dp, ds)
 		if (other_dp->type == DSA_PORT_TYPE_CPU ||
@@ -2487,6 +2494,10 @@ static int mv88e6xxx_port_bridge_join(struct dsa_switch *ds, int port,
 	if (err)
 		goto unlock;
 
+	err = mv88e6xxx_port_set_map_da(chip, port, true);
+	if (err)
+		return err;
+
 	err = mv88e6xxx_port_commit_pvid(chip, port);
 	if (err)
 		goto unlock;
@@ -2521,6 +2532,12 @@ static void mv88e6xxx_port_bridge_leave(struct dsa_switch *ds, int port,
 	    mv88e6xxx_port_vlan_map(chip, port))
 		dev_err(ds->dev, "failed to remap in-chip Port VLAN\n");
 
+	err = mv88e6xxx_port_set_map_da(chip, port, false);
+	if (err)
+		dev_err(ds->dev,
+			"port %d failed to restore map-DA: %pe\n",
+			port, ERR_PTR(err));
+
 	err = mv88e6xxx_port_commit_pvid(chip, port);
 	if (err)
 		dev_err(ds->dev,
@@ -2918,12 +2935,13 @@ static int mv88e6xxx_setup_port(struct mv88e6xxx_chip *chip, int port)
 		return err;
 
 	/* Port Control 2: don't force a good FCS, set the MTU size to
-	 * 10222 bytes, disable 802.1q tags checking, don't discard tagged or
-	 * untagged frames on this port, do a destination address lookup on all
-	 * received packets as usual, disable ARP mirroring and don't send a
-	 * copy of all transmitted/received frames on this port to the CPU.
+	 * 10222 bytes, disable 802.1q tags checking, don't discard
+	 * tagged or untagged frames on this port, skip destination
+	 * address lookup on user ports, disable ARP mirroring and don't
+	 * send a copy of all transmitted/received frames on this port
+	 * to the CPU.
 	 */
-	err = mv88e6xxx_port_set_map_da(chip, port);
+	err = mv88e6xxx_port_set_map_da(chip, port, !dsa_is_user_port(ds, port));
 	if (err)
 		return err;
 
diff --git a/drivers/net/dsa/mv88e6xxx/port.c b/drivers/net/dsa/mv88e6xxx/port.c
index ab41619a809b..ceb450113f88 100644
--- a/drivers/net/dsa/mv88e6xxx/port.c
+++ b/drivers/net/dsa/mv88e6xxx/port.c
@@ -1278,7 +1278,7 @@ int mv88e6xxx_port_drop_untagged(struct mv88e6xxx_chip *chip, int port,
 	return mv88e6xxx_port_write(chip, port, MV88E6XXX_PORT_CTL2, new);
 }
 
-int mv88e6xxx_port_set_map_da(struct mv88e6xxx_chip *chip, int port)
+int mv88e6xxx_port_set_map_da(struct mv88e6xxx_chip *chip, int port, bool map)
 {
 	u16 reg;
 	int err;
@@ -1287,7 +1287,10 @@ int mv88e6xxx_port_set_map_da(struct mv88e6xxx_chip *chip, int port)
 	if (err)
 		return err;
 
-	reg |= MV88E6XXX_PORT_CTL2_MAP_DA;
+	if (map)
+		reg |= MV88E6XXX_PORT_CTL2_MAP_DA;
+	else
+		reg &= ~MV88E6XXX_PORT_CTL2_MAP_DA;
 
 	return mv88e6xxx_port_write(chip, port, MV88E6XXX_PORT_CTL2, reg);
 }
diff --git a/drivers/net/dsa/mv88e6xxx/port.h b/drivers/net/dsa/mv88e6xxx/port.h
index 03382b66f800..5c347cc58baf 100644
--- a/drivers/net/dsa/mv88e6xxx/port.h
+++ b/drivers/net/dsa/mv88e6xxx/port.h
@@ -425,7 +425,7 @@ int mv88e6185_port_get_cmode(struct mv88e6xxx_chip *chip, int port, u8 *cmode);
 int mv88e6352_port_get_cmode(struct mv88e6xxx_chip *chip, int port, u8 *cmode);
 int mv88e6xxx_port_drop_untagged(struct mv88e6xxx_chip *chip, int port,
 				 bool drop_untagged);
-int mv88e6xxx_port_set_map_da(struct mv88e6xxx_chip *chip, int port);
+int mv88e6xxx_port_set_map_da(struct mv88e6xxx_chip *chip, int port, bool map);
 int mv88e6095_port_set_upstream_port(struct mv88e6xxx_chip *chip, int port,
 				     int upstream_port);
 int mv88e6xxx_port_set_mirror(struct mv88e6xxx_chip *chip, int port,
diff --git a/include/net/dsa.h b/include/net/dsa.h
index 43c4153ef53a..6e5ef62a7dce 100644
--- a/include/net/dsa.h
+++ b/include/net/dsa.h
@@ -591,6 +591,18 @@ static inline bool dsa_is_upstream_port(struct dsa_switch *ds, int port)
 	return port == dsa_upstream_port(ds, port);
 }
 
+/* Return the local port used to reach the CPU port */
+static inline unsigned int dsa_switch_upstream_port(struct dsa_switch *ds)
+{
+	struct dsa_port *dp;
+
+	dsa_switch_for_each_available_port(dp, ds) {
+		return dsa_upstream_port(ds, dp->index);
+	}
+
+	return ds->num_ports;
+}
+
 /* Return true if @upstream_ds is an upstream switch of @downstream_ds, meaning
  * that the routing port from @downstream_ds to @upstream_ds is also the port
  * which @downstream_ds uses to reach its dedicated CPU.
-- 
2.25.1

Re: [PATCH v2 net-next 1/5] net: dsa: mv88e6xxx: Improve isolation of standalone ports

[Vladimir Oltean]

On Thu, Feb 03, 2022 at 11:16:53AM +0100, Tobias Waldekranz wrote:
> Clear MapDA on standalone ports to bypass any ATU lookup that might
> point the packet in the wrong direction. This means that all packets
> are flooded using the PVT config. So make sure that standalone ports
> are only allowed to communicate with the local upstream port.
> 
> Here is a scenario in which this is needed:
> 
>    CPU
>     |     .----.
> .---0---. | .--0--.
> |  sw0  | | | sw1 |
> '-1-2-3-' | '-1-2-'
>       '---'
> 
> - sw0p1 and sw1p1 are bridged
> - sw0p2 and sw1p2 are in standalone mode
> - Learning must be enabled on sw0p3 in order for hardware forwarding
>   to work properly between bridged ports
> 
> 1. A packet with SA :aa comes in on sw1p2
>    1a. Egresses sw1p0
>    1b. Ingresses sw0p3, ATU adds an entry for :aa towards port 3
>    1c. Egresses sw0p0
> 
> 2. A packet with DA :aa comes in on sw0p2
>    2a. If an ATU lookup is done at this point, the packet will be
>        incorrectly forwarded towards sw0p3. With this change in place,
>        the ATU is bypassed and the packet is forwarded in accordance
>        with the PVT, which only contains the CPU port.
> 
> Signed-off-by: Tobias Waldekranz <tobias@waldekranz.com>
> ---

Reviewed-by: Vladimir Oltean <olteanv@gmail.com>

[PATCH v2 net-next 2/5] net: dsa: mv88e6xxx: Support policy entries in the VTU

[Tobias Waldekranz]

A VTU entry with policy enabled is used in combination with a port's
VTU policy setting to override normal switching behavior for frames
assigned to the entry's VID.

A typical example is to Treat all frames in a particular VLAN as
control traffic, and trap them to the CPU. In which case the relevant
user port's VTU policy would be set to TRAP.

Signed-off-by: Tobias Waldekranz <tobias@waldekranz.com>
---
 drivers/net/dsa/mv88e6xxx/chip.h        | 1 +
 drivers/net/dsa/mv88e6xxx/global1.h     | 1 +
 drivers/net/dsa/mv88e6xxx/global1_vtu.c | 5 ++++-
 3 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/net/dsa/mv88e6xxx/chip.h b/drivers/net/dsa/mv88e6xxx/chip.h
index 438cee853d07..80dc7b549e81 100644
--- a/drivers/net/dsa/mv88e6xxx/chip.h
+++ b/drivers/net/dsa/mv88e6xxx/chip.h
@@ -179,6 +179,7 @@ struct mv88e6xxx_vtu_entry {
 	u16	fid;
 	u8	sid;
 	bool	valid;
+	bool	policy;
 	u8	member[DSA_MAX_PORTS];
 	u8	state[DSA_MAX_PORTS];
 };
diff --git a/drivers/net/dsa/mv88e6xxx/global1.h b/drivers/net/dsa/mv88e6xxx/global1.h
index 4f3dbb015f77..2c1607c858a1 100644
--- a/drivers/net/dsa/mv88e6xxx/global1.h
+++ b/drivers/net/dsa/mv88e6xxx/global1.h
@@ -46,6 +46,7 @@
 
 /* Offset 0x02: VTU FID Register */
 #define MV88E6352_G1_VTU_FID		0x02
+#define MV88E6352_G1_VTU_FID_VID_POLICY	0x1000
 #define MV88E6352_G1_VTU_FID_MASK	0x0fff
 
 /* Offset 0x03: VTU SID Register */
diff --git a/drivers/net/dsa/mv88e6xxx/global1_vtu.c b/drivers/net/dsa/mv88e6xxx/global1_vtu.c
index ae12c981923e..b1bd9274a562 100644
--- a/drivers/net/dsa/mv88e6xxx/global1_vtu.c
+++ b/drivers/net/dsa/mv88e6xxx/global1_vtu.c
@@ -27,7 +27,7 @@ static int mv88e6xxx_g1_vtu_fid_read(struct mv88e6xxx_chip *chip,
 		return err;
 
 	entry->fid = val & MV88E6352_G1_VTU_FID_MASK;
-
+	entry->policy = !!(val & MV88E6352_G1_VTU_FID_VID_POLICY);
 	return 0;
 }
 
@@ -36,6 +36,9 @@ static int mv88e6xxx_g1_vtu_fid_write(struct mv88e6xxx_chip *chip,
 {
 	u16 val = entry->fid & MV88E6352_G1_VTU_FID_MASK;
 
+	if (entry->policy)
+		val |= MV88E6352_G1_VTU_FID_VID_POLICY;
+
 	return mv88e6xxx_g1_write(chip, MV88E6352_G1_VTU_FID, val);
 }
 
-- 
2.25.1

[PATCH v2 net-next 3/5] net: dsa: mv88e6xxx: Enable port policy support on 6097

[Tobias Waldekranz]

This chip has support for the same per-port policy actions found in
later versions of LinkStreet devices.

Fixes: f3a2cd326e44 ("net: dsa: mv88e6xxx: introduce .port_set_policy")
Signed-off-by: Tobias Waldekranz <tobias@waldekranz.com>
---
 drivers/net/dsa/mv88e6xxx/chip.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
index 7f02ec502e71..99151ba6f545 100644
--- a/drivers/net/dsa/mv88e6xxx/chip.c
+++ b/drivers/net/dsa/mv88e6xxx/chip.c
@@ -3652,6 +3652,7 @@ static const struct mv88e6xxx_ops mv88e6097_ops = {
 	.port_sync_link = mv88e6185_port_sync_link,
 	.port_set_speed_duplex = mv88e6185_port_set_speed_duplex,
 	.port_tag_remap = mv88e6095_port_tag_remap,
+	.port_set_policy = mv88e6352_port_set_policy,
 	.port_set_frame_mode = mv88e6351_port_set_frame_mode,
 	.port_set_ucast_flood = mv88e6352_port_set_ucast_flood,
 	.port_set_mcast_flood = mv88e6352_port_set_mcast_flood,
-- 
2.25.1

[PATCH v2 net-next 4/5] net: dsa: mv88e6xxx: Improve multichip isolation of standalone ports

[Tobias Waldekranz]

Given that standalone ports are now configured to bypass the ATU and
forward all frames towards the upstream port, extend the ATU bypass to
multichip systems.

Load VID 0 (standalone) into the VTU with the policy bit set. Since
VID 4095 (bridged) is already loaded, we now know that all VIDs in use
are always available in all VTUs. Therefore, we can safely enable
802.1Q on DSA ports.

Setting the DSA ports' VTU policy to TRAP means that all incoming
frames on VID 0 will be classified as MGMT - as a result, the ATU is
bypassed on all subsequent switches.

With this isolation in place, we are able to support configurations
that are simultaneously very quirky and very useful. Quirky because it
involves looping cables between local switchports like in this
example:

   CPU
    |     .------.
.---0---. | .----0----.
|  sw0  | | |   sw1   |
'-1-2-3-' | '-1-2-3-4-'
  $ @ '---'   $ @ % %

We have three physically looped pairs ($, @, and %).

This is very useful because it allows us to run the kernel's
kselftests for the bridge on mv88e6xxx hardware.

Signed-off-by: Tobias Waldekranz <tobias@waldekranz.com>
---
 drivers/net/dsa/mv88e6xxx/chip.c | 64 ++++++++++++++++++++++----------
 include/net/dsa.h                |  6 +++
 2 files changed, 51 insertions(+), 19 deletions(-)

diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
index 99151ba6f545..22391f8d4169 100644
--- a/drivers/net/dsa/mv88e6xxx/chip.c
+++ b/drivers/net/dsa/mv88e6xxx/chip.c
@@ -1630,21 +1630,11 @@ static int mv88e6xxx_fid_map_vlan(struct mv88e6xxx_chip *chip,
 
 int mv88e6xxx_fid_map(struct mv88e6xxx_chip *chip, unsigned long *fid_bitmap)
 {
-	int i, err;
-	u16 fid;
-
 	bitmap_zero(fid_bitmap, MV88E6XXX_N_FID);
 
-	/* Set every FID bit used by the (un)bridged ports */
-	for (i = 0; i < mv88e6xxx_num_ports(chip); ++i) {
-		err = mv88e6xxx_port_get_fid(chip, i, &fid);
-		if (err)
-			return err;
-
-		set_bit(fid, fid_bitmap);
-	}
-
-	/* Set every FID bit used by the VLAN entries */
+	/* Every FID has an associated VID, so walking the VTU
+	 * will discover the full set of FIDs in use.
+	 */
 	return mv88e6xxx_vtu_walk(chip, mv88e6xxx_fid_map_vlan, fid_bitmap);
 }
 
@@ -1657,10 +1647,7 @@ static int mv88e6xxx_atu_new(struct mv88e6xxx_chip *chip, u16 *fid)
 	if (err)
 		return err;
 
-	/* The reset value 0x000 is used to indicate that multiple address
-	 * databases are not needed. Return the next positive available.
-	 */
-	*fid = find_next_zero_bit(fid_bitmap, MV88E6XXX_N_FID, 1);
+	*fid = find_first_zero_bit(fid_bitmap, MV88E6XXX_N_FID);
 	if (unlikely(*fid >= mv88e6xxx_num_databases(chip)))
 		return -ENOSPC;
 
@@ -2152,6 +2139,9 @@ static int mv88e6xxx_port_vlan_join(struct mv88e6xxx_chip *chip, int port,
 	if (!vlan.valid) {
 		memset(&vlan, 0, sizeof(vlan));
 
+		if (vid == MV88E6XXX_VID_STANDALONE)
+			vlan.policy = true;
+
 		err = mv88e6xxx_atu_new(chip, &vlan.fid);
 		if (err)
 			return err;
@@ -2949,8 +2939,44 @@ static int mv88e6xxx_setup_port(struct mv88e6xxx_chip *chip, int port)
 	if (err)
 		return err;
 
+	/* On chips that support it, set all downstream DSA ports'
+	 * VLAN policy to TRAP. In combination with loading
+	 * MV88E6XXX_VID_STANDALONE as a policy entry in the VTU, this
+	 * provides a better isolation barrier between standalone
+	 * ports, as the ATU is bypassed on any intermediate switches
+	 * between the incoming port and the CPU.
+	 */
+	if (dsa_is_downstream_port(ds, port) &&
+	    chip->info->ops->port_set_policy) {
+		err = chip->info->ops->port_set_policy(chip, port,
+						MV88E6XXX_POLICY_MAPPING_VTU,
+						MV88E6XXX_POLICY_ACTION_TRAP);
+		if (err)
+			return err;
+	}
+
+	/* User ports start out in standalone mode and 802.1Q is
+	 * therefore disabled. On DSA ports, all valid VIDs are always
+	 * loaded in the VTU - therefore, enable 802.1Q in order to take
+	 * advantage of VLAN policy on chips that supports it.
+	 */
 	err = mv88e6xxx_port_set_8021q_mode(chip, port,
-				MV88E6XXX_PORT_CTL2_8021Q_MODE_DISABLED);
+				dsa_is_user_port(ds, port) ?
+				MV88E6XXX_PORT_CTL2_8021Q_MODE_DISABLED :
+				MV88E6XXX_PORT_CTL2_8021Q_MODE_SECURE);
+	if (err)
+		return err;
+
+	/* Bind MV88E6XXX_VID_STANDALONE to MV88E6XXX_FID_STANDALONE by
+	 * virtue of the fact that mv88e6xxx_atu_new() will pick it as
+	 * the first free FID. This will be used as the private PVID for
+	 * unbridged ports. Shared (DSA and CPU) ports must also be
+	 * members of this VID, in order to trap all frames assigned to
+	 * it to the CPU.
+	 */
+	err = mv88e6xxx_port_vlan_join(chip, port, MV88E6XXX_VID_STANDALONE,
+				       MV88E6XXX_G1_VTU_DATA_MEMBER_TAG_UNMODIFIED,
+				       false);
 	if (err)
 		return err;
 
@@ -2963,7 +2989,7 @@ static int mv88e6xxx_setup_port(struct mv88e6xxx_chip *chip, int port)
 	 * relying on their port default FID.
 	 */
 	err = mv88e6xxx_port_vlan_join(chip, port, MV88E6XXX_VID_BRIDGED,
-				       MV88E6XXX_G1_VTU_DATA_MEMBER_TAG_UNTAGGED,
+				       MV88E6XXX_G1_VTU_DATA_MEMBER_TAG_UNMODIFIED,
 				       false);
 	if (err)
 		return err;
diff --git a/include/net/dsa.h b/include/net/dsa.h
index 6e5ef62a7dce..ca8c14b547b4 100644
--- a/include/net/dsa.h
+++ b/include/net/dsa.h
@@ -591,6 +591,12 @@ static inline bool dsa_is_upstream_port(struct dsa_switch *ds, int port)
 	return port == dsa_upstream_port(ds, port);
 }
 
+/* Return true if this is a DSA port leading away from the CPU */
+static inline bool dsa_is_downstream_port(struct dsa_switch *ds, int port)
+{
+	return dsa_is_dsa_port(ds, port) && !dsa_is_upstream_port(ds, port);
+}
+
 /* Return the local port used to reach the CPU port */
 static inline unsigned int dsa_switch_upstream_port(struct dsa_switch *ds)
 {
-- 
2.25.1

Re: [PATCH v2 net-next 4/5] net: dsa: mv88e6xxx: Improve multichip isolation of standalone ports

[Vladimir Oltean]

On Thu, Feb 03, 2022 at 11:16:56AM +0100, Tobias Waldekranz wrote:
> Given that standalone ports are now configured to bypass the ATU and
> forward all frames towards the upstream port, extend the ATU bypass to
> multichip systems.
> 
> Load VID 0 (standalone) into the VTU with the policy bit set. Since
> VID 4095 (bridged) is already loaded, we now know that all VIDs in use
> are always available in all VTUs. Therefore, we can safely enable
> 802.1Q on DSA ports.
> 
> Setting the DSA ports' VTU policy to TRAP means that all incoming
> frames on VID 0 will be classified as MGMT - as a result, the ATU is
> bypassed on all subsequent switches.
> 
> With this isolation in place, we are able to support configurations
> that are simultaneously very quirky and very useful. Quirky because it
> involves looping cables between local switchports like in this
> example:
> 
>    CPU
>     |     .------.
> .---0---. | .----0----.
> |  sw0  | | |   sw1   |
> '-1-2-3-' | '-1-2-3-4-'
>   $ @ '---'   $ @ % %
> 
> We have three physically looped pairs ($, @, and %).
> 
> This is very useful because it allows us to run the kernel's
> kselftests for the bridge on mv88e6xxx hardware.
> 
> Signed-off-by: Tobias Waldekranz <tobias@waldekranz.com>
> ---

Reviewed-by: Vladimir Oltean <olteanv@gmail.com>

[PATCH v2 net-next 5/5] selftests: net: bridge: Parameterize ageing timeout

[Tobias Waldekranz]

Allow the ageing timeout that is set on bridges to be customized from
forwarding.config. This allows the tests to be run on hardware which
does not support a 10s timeout (e.g. mv88e6xxx).

Signed-off-by: Tobias Waldekranz <tobias@waldekranz.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
---
 tools/testing/selftests/net/forwarding/bridge_vlan_aware.sh  | 5 +++--
 .../testing/selftests/net/forwarding/bridge_vlan_unaware.sh  | 5 +++--
 .../selftests/net/forwarding/forwarding.config.sample        | 2 ++
 tools/testing/selftests/net/forwarding/lib.sh                | 1 +
 4 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/net/forwarding/bridge_vlan_aware.sh b/tools/testing/selftests/net/forwarding/bridge_vlan_aware.sh
index b90dff8d3a94..64bd00fe9a4f 100755
--- a/tools/testing/selftests/net/forwarding/bridge_vlan_aware.sh
+++ b/tools/testing/selftests/net/forwarding/bridge_vlan_aware.sh
@@ -28,8 +28,9 @@ h2_destroy()
 
 switch_create()
 {
-	# 10 Seconds ageing time.
-	ip link add dev br0 type bridge vlan_filtering 1 ageing_time 1000 \
+	ip link add dev br0 type bridge \
+		vlan_filtering 1 \
+		ageing_time $LOW_AGEING_TIME \
 		mcast_snooping 0
 
 	ip link set dev $swp1 master br0
diff --git a/tools/testing/selftests/net/forwarding/bridge_vlan_unaware.sh b/tools/testing/selftests/net/forwarding/bridge_vlan_unaware.sh
index c15c6c85c984..1c8a26046589 100755
--- a/tools/testing/selftests/net/forwarding/bridge_vlan_unaware.sh
+++ b/tools/testing/selftests/net/forwarding/bridge_vlan_unaware.sh
@@ -27,8 +27,9 @@ h2_destroy()
 
 switch_create()
 {
-	# 10 Seconds ageing time.
-	ip link add dev br0 type bridge ageing_time 1000 mcast_snooping 0
+	ip link add dev br0 type bridge \
+		ageing_time $LOW_AGEING_TIME \
+		mcast_snooping 0
 
 	ip link set dev $swp1 master br0
 	ip link set dev $swp2 master br0
diff --git a/tools/testing/selftests/net/forwarding/forwarding.config.sample b/tools/testing/selftests/net/forwarding/forwarding.config.sample
index b0980a2efa31..4a546509de90 100644
--- a/tools/testing/selftests/net/forwarding/forwarding.config.sample
+++ b/tools/testing/selftests/net/forwarding/forwarding.config.sample
@@ -41,6 +41,8 @@ NETIF_CREATE=yes
 # Timeout (in seconds) before ping exits regardless of how many packets have
 # been sent or received
 PING_TIMEOUT=5
+# Minimum ageing_time (in centiseconds) supported by hardware
+LOW_AGEING_TIME=1000
 # Flag for tc match, supposed to be skip_sw/skip_hw which means do not process
 # filter by software/hardware
 TC_FLAG=skip_hw
diff --git a/tools/testing/selftests/net/forwarding/lib.sh b/tools/testing/selftests/net/forwarding/lib.sh
index 7da783d6f453..e7e434a4758b 100644
--- a/tools/testing/selftests/net/forwarding/lib.sh
+++ b/tools/testing/selftests/net/forwarding/lib.sh
@@ -24,6 +24,7 @@ PING_COUNT=${PING_COUNT:=10}
 PING_TIMEOUT=${PING_TIMEOUT:=5}
 WAIT_TIMEOUT=${WAIT_TIMEOUT:=20}
 INTERFACE_TIMEOUT=${INTERFACE_TIMEOUT:=600}
+LOW_AGEING_TIME=${LOW_AGEING_TIME:=1000}
 REQUIRE_JQ=${REQUIRE_JQ:=yes}
 REQUIRE_MZ=${REQUIRE_MZ:=yes}
 
-- 
2.25.1