[PATCH v4 1/2] PCI: AtomicOps: Do not enable if root-port capabilities are unknown
From: Gerd Bayer <gbayer@linux.ibm.com>
Date: 2026-03-13 16:50:03
Also in:
linux-pci, linux-rdma, linux-s390, lkml, stable
Subsystem:
pci subsystem, the rest · Maintainers:
Bjorn Helgaas, Linus Torvalds
When inspecting the config space of a Connect-X physical function in an
s390 system after it was initialized by the mlx5_core device driver, we
found the function to be enabled to request AtomicOps despite the
system's root-complex lacking support for completing them:
1ed0:00:00.1 Ethernet controller: Mellanox Technologies MT2894 Family [ConnectX-6 Lx]
Subsystem: Mellanox Technologies Device 0002
[...]
DevCtl2: Completion Timeout: 50us to 50ms, TimeoutDis-
AtomicOpsCtl: ReqEn+
IDOReq- IDOCompl- LTR- EmergencyPowerReductionReq-
10BitTagReq- OBFF Disabled, EETLPPrefixBlk-
Turns out the device driver calls pci_enable_atomic_ops_to_root() which
defaulted to enable AtomicOps requests even if it had no information
about the root-port that the PCIe device is attached to.
Change to logic of pci_enable_atomic_ops_to_root() to fully traverse the
PCIe tree upwards, check that the bridge devices support delivering
AtomicOps transactions, and finally check that there is a root-port at
the end that does support completing AtomicOps.
Do not enable AtomicOps requests if nothing can be learned about how the
device is attached - e.g. if it is on an "isolated" bus, as in s390.
Reported-by: Alexander Schmidt <redacted>
Cc: stable@vger.kernel.org
Fixes: 430a23689dea ("PCI: Add pci_enable_atomic_ops_to_root()")
Signed-off-by: Gerd Bayer <gbayer@linux.ibm.com>
---
drivers/pci/pci.c | 30 ++++++++++++++----------------
1 file changed, 14 insertions(+), 16 deletions(-)
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 8479c2e1f74f1044416281aba11bf071ea89488a..94e90988df86b3278b1b6abbc326abf9b4a4a962 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c@@ -3676,7 +3676,7 @@ void pci_acs_init(struct pci_dev *dev) int pci_enable_atomic_ops_to_root(struct pci_dev *dev, u32 cap_mask) { struct pci_bus *bus = dev->bus; - struct pci_dev *bridge; + struct pci_dev *bridge = NULL; u32 cap, ctl2; /*
@@ -3714,29 +3714,27 @@ int pci_enable_atomic_ops_to_root(struct pci_dev *dev, u32 cap_mask) switch (pci_pcie_type(bridge)) { /* Ensure switch ports support AtomicOp routing */ case PCI_EXP_TYPE_UPSTREAM: - case PCI_EXP_TYPE_DOWNSTREAM: - if (!(cap & PCI_EXP_DEVCAP2_ATOMIC_ROUTE)) - return -EINVAL; - break; - - /* Ensure root port supports all the sizes we care about */ - case PCI_EXP_TYPE_ROOT_PORT: - if ((cap & cap_mask) != cap_mask) - return -EINVAL; - break; - } - - /* Ensure upstream ports don't block AtomicOps on egress */ - if (pci_pcie_type(bridge) == PCI_EXP_TYPE_UPSTREAM) { + /* Upstream ports must not block AtomicOps on egress */ pcie_capability_read_dword(bridge, PCI_EXP_DEVCTL2, &ctl2); if (ctl2 & PCI_EXP_DEVCTL2_ATOMIC_EGRESS_BLOCK) return -EINVAL; + fallthrough; + /* All switch ports need to route AtomicOps */ + case PCI_EXP_TYPE_DOWNSTREAM: + if (!(cap & PCI_EXP_DEVCAP2_ATOMIC_ROUTE)) + return -EINVAL; + break; } - bus = bus->parent; } + /* Finally, last bridge must be root port and support requested sizes */ + if ((!bridge) || + (pci_pcie_type(bridge) != PCI_EXP_TYPE_ROOT_PORT) || + ((cap & cap_mask) != cap_mask)) + return -EINVAL; + pcie_capability_set_word(dev, PCI_EXP_DEVCTL2, PCI_EXP_DEVCTL2_ATOMIC_REQ); return 0;
--
2.51.0