[PATCH v6 1/2] PCI: AtomicOps: Do not enable without support in root complex
From: Gerd Bayer <gbayer@linux.ibm.com>
Date: 2026-03-25 15:16:34
Also in:
linux-pci, linux-rdma, linux-s390, lkml, stable
Subsystem:
pci subsystem, s390 architecture, s390 pci subsystem, the rest · Maintainers:
Bjorn Helgaas, Heiko Carstens, Vasily Gorbik, Alexander Gordeev, Niklas Schnelle, Gerd Bayer, 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. Similarly,
AtomicOps requests are enabled for root complex integrated endpoints
(RCiEPs) unconditionally.
Change the 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 - or that the support for
completing AtomicOps at the root complex is announced through some other
arch specific way.
Introduce a new pcibios_connects_to_atomicops_capable_rc() function to
implement the check - and default to always "true". This leaves the
semantics for today's RCiEPs intact. Pass in the device in question and
the requested capabilities for future expansions.
For s390, override pcibios_connects_to_atomicops_capable_rc() to
always return "false".
Do not change the enablement of AtomicOps requests if there is no
positive confirmation that the root complex can complete PCIe AtomicOps.
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>
---
arch/s390/pci/pci.c | 5 +++++
drivers/pci/pci.c | 48 +++++++++++++++++++++++++++++++-----------------
include/linux/pci.h | 1 +
3 files changed, 37 insertions(+), 17 deletions(-)
diff --git a/arch/s390/pci/pci.c b/arch/s390/pci/pci.c
index 2a430722cbe415dd56c92fed2e513e524f46481a..a0bef77082a153a258fbe4abb1070b22e020888e 100644
--- a/arch/s390/pci/pci.c
+++ b/arch/s390/pci/pci.c@@ -265,6 +265,11 @@ static int zpci_cfg_store(struct zpci_dev *zdev, int offset, u32 val, u8 len) return rc; } +bool pcibios_connects_to_atomicops_capable_rc(struct pci_dev *dev, u32 cap_mask) +{ + return false; +} + resource_size_t pcibios_align_resource(void *data, const struct resource *res, resource_size_t size, resource_size_t align)
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 8479c2e1f74f1044416281aba11bf071ea89488a..006aa589926cb290de43f152100ddaf9961407d1 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c@@ -3660,6 +3660,19 @@ void pci_acs_init(struct pci_dev *dev) pci_disable_broken_acs_cap(dev); } +static bool pci_is_atomicops_capable_rp(struct pci_dev *dev, u32 cap, u32 cap_mask) +{ + if (!dev || !(pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT)) + return false; + + return (cap & cap_mask) == cap_mask; +} + +bool __weak pcibios_connects_to_atomicops_capable_rc(struct pci_dev *dev, u32 cap_mask) +{ + return true; +} + /** * pci_enable_atomic_ops_to_root - enable AtomicOp requests to root port * @dev: the PCI device
@@ -3676,8 +3689,9 @@ 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; - u32 cap, ctl2; + struct pci_dev *bridge = NULL; + u32 cap = 0; + u32 ctl2; /* * Per PCIe r5.0, sec 9.3.5.10, the AtomicOp Requester Enable bit
@@ -3714,29 +3728,29 @@ 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 + * or firmware asserts support + */ + if (!(pci_is_atomicops_capable_rp(bridge, cap, cap_mask) || + pcibios_connects_to_atomicops_capable_rc(dev, cap_mask))) + return -EINVAL; + pcie_capability_set_word(dev, PCI_EXP_DEVCTL2, PCI_EXP_DEVCTL2_ATOMIC_REQ); return 0;
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 1c270f1d512301de4d462fe7e5097c32af5c6f8d..ef90604c39859ea8e61e5392d0bdaa1b0e43874b 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h@@ -692,6 +692,7 @@ void pci_set_host_bridge_release(struct pci_host_bridge *bridge, void *release_data); int pcibios_root_bridge_prepare(struct pci_host_bridge *bridge); +bool pcibios_connects_to_atomicops_capable_rc(struct pci_dev *dev, u32 cap_mask); #define PCI_REGION_FLAG_MASK 0x0fU /* These bits of resource flags tell us the PCI region flags */
--
2.51.0