[PATCH net v2] pds_core: fix cmd_regs access racing BAR unmap on reset

pdsc_reset_prepare() and pdsc_reset_done()'s pdsc_map_bars() error path
clear/iounmap cmd_regs without devcmd_lock, and some devcmd callers
access cmd_regs under the lock without checking it. An FLR concurrent
with a devlink flash can unmap cmd_regs under an in-flight devcmd,
causing a NULL deref or a write to unmapped MMIO.

Take devcmd_lock across the BAR unmap/remap, and check cmd_regs at those
callers. Only the PF maps cmd_regs and runs devcmd, so skip the unmap on
a VF, as pdsc_remove() and pdsc_reset_done() already do.

pdsc_unmap_bars() also clears info_regs, intr_status, intr_ctrl and
db_pages. The interrupt and start/stop readers of those are quiesced
before the unmap by pdsc_fw_down(), which frees the interrupts and tears
down the queues. The debugfs readers are not, since those files outlive
a reset; that is pre-existing and out of scope here.

Fixes: e96094c1d11c ("pds_core: Clear BARs on reset")
Reported-by: sashiko-bot <[email protected]>
Closes: https://sashiko.dev/#/patchset/20260708212222.296202-1-nikhil.rao%40amd.com?part=3
Assisted-by: Claude:claude-opus-4.8
Signed-off-by: Nikhil P. Rao <[email protected]>
---
v2: address sashiko findings on v1
  - guard cmd_regs under devcmd_lock in pdsc_identify() and
    pdsc_core_init(), which stage into cmd_regs->data before
    pdsc_devcmd_locked()'s check
  - skip the unmap for VFs instead of running it unlocked; it is a
    no-op there
  - the download loop is left as-is: an interrupted flash is not
    committed, as the device validates on install and reports
    PDS_RC_BAD_FW
  - say why the other BAR0-backed pointers (intr_status, intr_ctrl,
    db_pages) are not affected, and what remains out of scope
  - rebased on net
v1: https://lore.kernel.org/all/[email protected]/

 drivers/net/ethernet/amd/pds_core/core.c | 8 ++++++++
 drivers/net/ethernet/amd/pds_core/dev.c  | 5 +++++
 drivers/net/ethernet/amd/pds_core/fw.c   | 6 ++++++
 drivers/net/ethernet/amd/pds_core/main.c | 8 +++++++-
 4 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/amd/pds_core/core.c b/drivers/net/ethernet/amd/pds_core/core.c
index 04ec2569c61c..c3c27a7c63d0 100644
--- a/drivers/net/ethernet/amd/pds_core/core.c
+++ b/drivers/net/ethernet/amd/pds_core/core.c
@@ -364,6 +364,14 @@ static int pdsc_core_init(struct pdsc *pdsc)
 
 	mutex_lock(&pdsc->devcmd_lock);
 
+	if (!pdsc->cmd_regs) {
+		mutex_unlock(&pdsc->devcmd_lock);
+		err = -ENXIO;
+		dev_err(pdsc->dev, "Device init command failed: %pe\n",
+			ERR_PTR(err));
+		goto err_out_uninit;
+	}
+
 	sz = min_t(size_t, sizeof(cidi), sizeof(pdsc->cmd_regs->data));
 	memcpy_toio(&pdsc->cmd_regs->data, &cidi, sz);
 
diff --git a/drivers/net/ethernet/amd/pds_core/dev.c b/drivers/net/ethernet/amd/pds_core/dev.c
index bded6b33289c..ec96f67dc67b 100644
--- a/drivers/net/ethernet/amd/pds_core/dev.c
+++ b/drivers/net/ethernet/amd/pds_core/dev.c
@@ -294,6 +294,11 @@ static int pdsc_identify(struct pdsc *pdsc)
 	 */
 	mutex_lock(&pdsc->devcmd_lock);
 
+	if (!pdsc->cmd_regs) {
+		mutex_unlock(&pdsc->devcmd_lock);
+		return -ENXIO;
+	}
+
 	sz = min_t(size_t, sizeof(drv), sizeof(pdsc->cmd_regs->data));
 	memcpy_toio(&pdsc->cmd_regs->data, &drv, sz);
 
diff --git a/drivers/net/ethernet/amd/pds_core/fw.c b/drivers/net/ethernet/amd/pds_core/fw.c
index fa626719e68d..cd7616ed9ef3 100644
--- a/drivers/net/ethernet/amd/pds_core/fw.c
+++ b/drivers/net/ethernet/amd/pds_core/fw.c
@@ -134,6 +134,12 @@ int pdsc_firmware_update(struct pdsc *pdsc, const struct firmware *fw,
 
 		copy_sz = min_t(unsigned int, buf_sz, fw->size - offset);
 		mutex_lock(&pdsc->devcmd_lock);
+		if (!pdsc->cmd_regs) {
+			mutex_unlock(&pdsc->devcmd_lock);
+			err = -ENXIO;
+			NL_SET_ERR_MSG_MOD(extack, "Device reset during flash");
+			goto err_out;
+		}
 		memcpy_toio(&pdsc->cmd_regs->data, fw->data + offset, copy_sz);
 		err = pdsc_devcmd_fw_download_locked(pdsc, data_addr,
 						     offset, copy_sz);
diff --git a/drivers/net/ethernet/amd/pds_core/main.c b/drivers/net/ethernet/amd/pds_core/main.c
index 9a2c64198d03..1b960139de4e 100644
--- a/drivers/net/ethernet/amd/pds_core/main.c
+++ b/drivers/net/ethernet/amd/pds_core/main.c
@@ -507,7 +507,11 @@ static void pdsc_reset_prepare(struct pci_dev *pdev)
 		pdsc_auxbus_dev_del(pdsc, pdsc, &pdsc->padev);
 	}
 
-	pdsc_unmap_bars(pdsc);
+	if (!pdev->is_virtfn) {
+		mutex_lock(&pdsc->devcmd_lock);
+		pdsc_unmap_bars(pdsc);
+		mutex_unlock(&pdsc->devcmd_lock);
+	}
 	pci_release_regions(pdev);
 	if (pci_is_enabled(pdev))
 		pci_disable_device(pdev);
@@ -536,7 +540,9 @@ static void pdsc_reset_done(struct pci_dev *pdev)
 			return;
 		}
 
+		mutex_lock(&pdsc->devcmd_lock);
 		err = pdsc_map_bars(pdsc);
+		mutex_unlock(&pdsc->devcmd_lock);
 		if (err)
 			return;
 	}
-- 
2.43.0