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

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Date: Mon, 1 Jul 2024 18:41:55 +0200
From: Petr Machata <petrm@...dia.com>
To: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
	<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>, <netdev@...r.kernel.org>
CC: Petr Machata <petrm@...dia.com>, Ido Schimmel <idosch@...dia.com>,
	<mlxsw@...dia.com>, <linux-pci@...r.kernel.org>
Subject: [PATCH net-next 3/3] mlxsw: pci: Lock configuration space of upstream bridge during reset

From: Ido Schimmel <idosch@...dia.com>

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

[1] https://lore.kernel.org/all/171711746953.1628941.4692125082286867825.stgit@dwillia2-xfh.jf.intel.com/
[2] https://lore.kernel.org/all/20240531213150.GA610983@bhelgaas/

Cc: linux-pci@...r.kernel.org
Signed-off-by: Ido Schimmel <idosch@...dia.com>
Signed-off-by: Petr Machata <petrm@...dia.com>
---
 drivers/net/ethernet/mellanox/mlxsw/pci.c | 6 ++++++
 1 file changed, 6 insertions(+)

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;
 }
-- 
2.45.0