[PATCH v6 01/17] PCI: Don't suspend IOMMU when probing reset capability

[Nicolin Chen <nicolinc@nvidia.com>]

reset_method_store() in drivers/pci/pci-sysfs.c discovers supported reset
methods by calling reset_fn(pdev, PCI_RESET_PROBE, ...) without holding a
device_lock, since the probe path is expected to query the device's reset
capability without changing device state.

However, pci_reset_bus_function() and __pci_dev_specific_reset() violate
that contract after pci_dev_reset_iommu_prepare/done() were added, which
moves the device into a blocking domain and abruptly aborts any in-flight
DMA. Doing this for a probe -- a state-query call that does not even hold
device_lock -- can cause driver timeouts and data loss on a DMAing device.

The peer reset helpers all handle this correctly: they short-circuit on a
probe input before touching the IOMMU.

Skip pci_dev_reset_iommu_prepare()/_done() entirely when probe is set. The
inner reset routines already implement their own probe semantics, and they
perform the capability checks and return without changing device state.

Fixes: f5b16b802174 ("PCI: Suspend iommu function prior to resetting a device")
Cc: stable@vger.kernel.org
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Assisted-by: LLM
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
---
 drivers/pci/pci.c    | 13 ++++++++-----
 drivers/pci/quirks.c | 13 ++++++++-----
 2 files changed, 16 insertions(+), 10 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index b2879a6be5f80..1eba412b7e0de 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -4996,10 +4996,12 @@ static int pci_reset_bus_function(struct pci_dev *dev, bool probe)
 	if (bridge && pcie_is_cxl(bridge) && cxl_sbr_masked(bridge))
 		return -ENOTTY;
 
-	rc = pci_dev_reset_iommu_prepare(dev);
-	if (rc) {
-		pci_err(dev, "failed to stop IOMMU for a PCI reset: %d\n", rc);
-		return rc;
+	if (!probe) {
+		rc = pci_dev_reset_iommu_prepare(dev);
+		if (rc) {
+			pci_err(dev, "failed to stop IOMMU for a PCI reset: %d\n", rc);
+			return rc;
+		}
 	}
 
 	rc = pci_dev_reset_slot_function(dev, probe);
@@ -5008,7 +5010,8 @@ static int pci_reset_bus_function(struct pci_dev *dev, bool probe)
 
 	rc = pci_parent_bus_reset(dev, probe);
 done:
-	pci_dev_reset_iommu_done(dev);
+	if (!probe)
+		pci_dev_reset_iommu_done(dev);
 	return rc;
 }
 
diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
index de9bbccda21fd..7858a063929d9 100644
--- a/drivers/pci/quirks.c
+++ b/drivers/pci/quirks.c
@@ -4253,14 +4253,17 @@ static int __pci_dev_specific_reset(struct pci_dev *dev, bool probe,
 {
 	int ret;
 
-	ret = pci_dev_reset_iommu_prepare(dev);
-	if (ret) {
-		pci_err(dev, "failed to stop IOMMU for a PCI reset: %d\n", ret);
-		return ret;
+	if (!probe) {
+		ret = pci_dev_reset_iommu_prepare(dev);
+		if (ret) {
+			pci_err(dev, "failed to stop IOMMU for a PCI reset: %d\n", ret);
+			return ret;
+		}
 	}
 
 	ret = i->reset(dev, probe);
-	pci_dev_reset_iommu_done(dev);
+	if (!probe)
+		pci_dev_reset_iommu_done(dev);
 	return ret;
 }
 
-- 
2.43.0