[net-next,v2,3/3] mlxsw: pci: Lock configuration space of upstream bridge during reset

Commit Message

Petr Machata July 8, 2024, 2:23 p.m. UTC

From: Ido Schimmel <[e-mail]>

The driver triggers a "Secondary Bus Reset" (SBR) by calling
__pci_reset_function_locked() which asserts the SBR bit in the "Bridge
Control Register" in the configuration space of the upstream bridge for
2ms. This is done without locking the configuration space of the
upstream bridge port, allowing user space to access it concurrently.

Linux 6.11 will start warning about such unlocked resets [1][2]:

pcieport 0000:00:01.0: unlocked secondary bus reset via: pci_reset_bus_function+0x51c/0x6a0

Avoid the warning and the concurrent access by locking the configuration
space of the upstream bridge prior to the reset and unlocking it
afterwards.

[1] https://lore.kernel.org/all/[e-mail]/
[2] https://lore.kernel.org/all/20240531213150.GA610983@bhelgaas/

Cc: [e-mail]
Signed-off-by: Ido Schimmel <[e-mail]>
Signed-off-by: Petr Machata <[e-mail]>
---

Notes:
    v2:
    - reword the commit message to reflect the fact that the change both
      suppresses a warning and avoid concurrent access

 drivers/net/ethernet/mellanox/mlxsw/pci.c | 6 ++++++
 1 file changed, 6 insertions(+)

Patch

diff --git a/drivers/net/ethernet/mellanox/mlxsw/pci.c b/drivers/net/ethernet/mellanox/mlxsw/pci.c
index 0320dabd1380..060e5b939211 100644
--- a/drivers/net/ethernet/mellanox/mlxsw/pci.c
+++ b/drivers/net/ethernet/mellanox/mlxsw/pci.c
@@ -1784,6 +1784,7 @@  static int mlxsw_pci_reset_at_pci_disable(struct mlxsw_pci *mlxsw_pci,
 {
 	struct pci_dev *pdev = mlxsw_pci->pdev;
 	char mrsr_pl[MLXSW_REG_MRSR_LEN];
+	struct pci_dev *bridge;
 	int err;
 
 	if (!pci_reset_sbr_supported) {
@@ -1800,6 +1801,9 @@  static int mlxsw_pci_reset_at_pci_disable(struct mlxsw_pci *mlxsw_pci,
 sbr:
 	device_lock_assert(&pdev->dev);
 
+	bridge = pci_upstream_bridge(pdev);
+	if (bridge)
+		pci_cfg_access_lock(bridge);
 	pci_cfg_access_lock(pdev);
 	pci_save_state(pdev);
 
@@ -1809,6 +1813,8 @@  static int mlxsw_pci_reset_at_pci_disable(struct mlxsw_pci *mlxsw_pci,
 
 	pci_restore_state(pdev);
 	pci_cfg_access_unlock(pdev);
+	if (bridge)
+		pci_cfg_access_unlock(bridge);
 
 	return err;
 }