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Message-Id: <20251023-ari_no_bus_dev-v4-2-8482e2ed10bd@linux.ibm.com>
Date: Thu, 23 Oct 2025 17:20:42 +0200
From: Niklas Schnelle <schnelle@...ux.ibm.com>
To: Bjorn Helgaas <bhelgaas@...gle.com>
Cc: Jan Kiszka <jan.kiszka@...mens.com>, Huacai Chen <chenhuacai@...nel.org>,
linux-s390 <linux-s390@...r.kernel.org>, loongarch@...ts.linux.dev,
Farhan Ali <alifm@...ux.ibm.com>,
Matthew Rosato <mjrosato@...ux.ibm.com>,
Tianrui Zhao <zhaotianrui@...ngson.cn>,
Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
Alexander Gordeev <agordeev@...ux.ibm.com>,
Sven Schnelle <svens@...ux.ibm.com>,
Christian Borntraeger <borntraeger@...ux.ibm.com>,
Gerd Bayer <gbayer@...ux.ibm.com>, linux-s390@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
jailhouse-dev@...glegroups.com,
Niklas Schnelle <schnelle@...ux.ibm.com>
Subject: [PATCH v4 2/2] PCI: s390: Handle ARI on bus without associated
struct pci_dev
On s390 PCI busses are virtualized and the downstream ports are
invisible to the OS and self in struct pci_bus is NULL. This associated
struct pci_dev is however relied upon in pci_ari_enabled() to check
whether ARI is enabled for the bus. ARI is therefor always detected as
disabled. At the same time, firmware on s390 always enables and relies
upon ARI thus causing a mismatch.
Despite simply being a mismatch this causes problems as some PCI devices
present a different SR-IOV topology depending on PCI_SRIOV_CTRL_ARI.
A similar mismatch may occur with SR-IOV when virtfn_add_bus() creates new
busses with no associated struct pci_dev. Here too pci_ari_enabled()
on these busses returns false even if ARI is actually used.
Prevent both mismatches by moving the ari_enabled flag from struct
pci_dev to struct pci_bus making it independent from self in struct
pci_bus. Let the bus inherit the ari_enabled state from its parent bus
when there is no bridge device such that busses added by virtfn_add_bus()
match their parent. For s390 set ari_enabled when the device supports
ARI in the awareness that all PCIe ports on s390 systems are ARI
capable.
Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
---
arch/s390/pci/pci.c | 7 +++++++
arch/s390/pci/pci_bus.c | 10 ++++++++++
drivers/pci/pci.c | 4 ++--
drivers/pci/probe.c | 1 +
include/linux/pci.h | 4 ++--
5 files changed, 22 insertions(+), 4 deletions(-)
diff --git a/arch/s390/pci/pci.c b/arch/s390/pci/pci.c
index c82c577db2bcd2143476cb8189fd89b9a4dc9836..773c0cbfc313ea1a6419a44d6158397dd13f6e76 100644
--- a/arch/s390/pci/pci.c
+++ b/arch/s390/pci/pci.c
@@ -609,6 +609,13 @@ int pcibios_device_add(struct pci_dev *pdev)
continue;
pci_claim_resource(pdev, i);
}
+ /*
+ * The below is the s390 equivalent of pci_configure_ari()
+ * which we can't use directly because the bridge devices
+ * are hidden in firmware.
+ */
+ if (!pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_ARI))
+ zdev->zbus->bus->ari_enabled = 0;
return 0;
}
diff --git a/arch/s390/pci/pci_bus.c b/arch/s390/pci/pci_bus.c
index 45a1c36c5a54e3a841e61cc365d3f36e9a94ba50..c887e61eb384ca98ff27d4f8af69e58c715b5002 100644
--- a/arch/s390/pci/pci_bus.c
+++ b/arch/s390/pci/pci_bus.c
@@ -207,6 +207,16 @@ static int zpci_bus_create_pci_bus(struct zpci_bus *zbus, struct zpci_dev *fr, s
return -EFAULT;
}
+ /*
+ * On s390 PCI busses are virtualized and the bridge
+ * devices are invisible to the OS. Furthermore busses
+ * may exist without a devfn 0 function. Thus the normal
+ * ARI detection does not work. At the same time fw/hw
+ * has always enabled ARI when possible. Reflect the actual
+ * state by setting ari_enabled whenever a device on the bus
+ * supports it.
+ */
+ bus->ari_enabled = 1;
zbus->bus = bus;
return 0;
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index b14dd064006cca80ec5275e45a35d6dc2b4d0bbc..8ef3c68280a629449e0a2176d938bf987c68dddf 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -3532,11 +3532,11 @@ void pci_configure_ari(struct pci_dev *dev)
if (pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ARI)) {
pcie_capability_set_word(bridge, PCI_EXP_DEVCTL2,
PCI_EXP_DEVCTL2_ARI);
- bridge->ari_enabled = 1;
+ dev->bus->ari_enabled = 1;
} else {
pcie_capability_clear_word(bridge, PCI_EXP_DEVCTL2,
PCI_EXP_DEVCTL2_ARI);
- bridge->ari_enabled = 0;
+ dev->bus->ari_enabled = 0;
}
}
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 13495b12fbcfae4b890bbd4b2f913742adf6dfed..338bb7e6738d27865e3d50aa3094ca5ab29a6a47 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -1216,6 +1216,7 @@ static struct pci_bus *pci_alloc_child_bus(struct pci_bus *parent,
if (!bridge) {
child->dev.parent = parent->bridge;
+ child->ari_enabled = parent->ari_enabled;
goto add_dev;
}
diff --git a/include/linux/pci.h b/include/linux/pci.h
index d1fdf81fbe1e427aecbc951fa3fdf65c20450b05..a9c3dbf17339e523362bd179ad3c7c8c91293cf0 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -445,7 +445,6 @@ struct pci_dev {
unsigned int irq_reroute_variant:2; /* Needs IRQ rerouting variant */
unsigned int msi_enabled:1;
unsigned int msix_enabled:1;
- unsigned int ari_enabled:1; /* ARI forwarding */
unsigned int ats_enabled:1; /* Address Translation Svc */
unsigned int pasid_enabled:1; /* Process Address Space ID */
unsigned int pri_enabled:1; /* Page Request Interface */
@@ -691,6 +690,7 @@ struct pci_bus {
unsigned int is_added:1;
unsigned int unsafe_warn:1; /* warned about RW1C config write */
unsigned int flit_mode:1; /* Link in Flit mode */
+ unsigned int ari_enabled:1; /* ARI forwarding enabled */
};
#define to_pci_bus(n) container_of(n, struct pci_bus, dev)
@@ -2740,7 +2740,7 @@ static inline bool pci_is_dev_assigned(struct pci_dev *pdev)
*/
static inline bool pci_ari_enabled(struct pci_bus *bus)
{
- return bus->self && bus->self->ari_enabled;
+ return bus->ari_enabled;
}
/**
--
2.48.1
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