6.14-stable review patch. If anyone has any objections, please let me know.
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From: Robin Murphy robin.murphy@arm.com
commit da33e87bd2bfc63531cf7448a3cd7a3d42182f08 upstream.
Next up on our list of race windows to close is another one during iommu_device_register() - it's now OK again for multiple instances to run their bus_iommu_probe() in parallel, but an iommu_probe_device() can still also race against a running bus_iommu_probe(). As Johan has managed to prove, this has now become a lot more visible on DT platforms wth driver_async_probe where a client driver is attempting to probe in parallel with its IOMMU driver - although commit b46064a18810 ("iommu: Handle race with default domain setup") resolves this from the client driver's point of view, this isn't before of_iommu_configure() has had the chance to attempt to "replay" a probe that the bus walk hasn't even tried yet, and so still cause the out-of-order group allocation behaviour that we're trying to clean up (and now warning about).
The most reliable thing to do here is to explicitly keep track of the "iommu_device_register() is still running" state, so we can then special-case the ops lookup for the replay path (based on dev->iommu again) to let that think it's still waiting for the IOMMU driver to appear at all. This still leaves the longstanding theoretical case of iommu_bus_notifier() being triggered during bus_iommu_probe(), but it's not so simple to defer a notifier, and nobody's ever reported that being a visible issue, so let's quietly kick that can down the road for now...
Reported-by: Johan Hovold johan@kernel.org Fixes: bcb81ac6ae3c ("iommu: Get DT/ACPI parsing into the proper probe path") Signed-off-by: Robin Murphy robin.murphy@arm.com Link: https://lore.kernel.org/r/88d54c1b48fed8279aa47d30f3d75173685bb26a.174551648... Signed-off-by: Joerg Roedel jroedel@suse.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/iommu/iommu.c | 26 ++++++++++++++++++-------- include/linux/iommu.h | 2 ++ 2 files changed, 20 insertions(+), 8 deletions(-)
--- a/drivers/iommu/iommu.c +++ b/drivers/iommu/iommu.c @@ -273,6 +273,8 @@ int iommu_device_register(struct iommu_d err = bus_iommu_probe(iommu_buses[i]); if (err) iommu_device_unregister(iommu); + else + WRITE_ONCE(iommu->ready, true); return err; } EXPORT_SYMBOL_GPL(iommu_device_register); @@ -2801,31 +2803,39 @@ bool iommu_default_passthrough(void) } EXPORT_SYMBOL_GPL(iommu_default_passthrough);
-const struct iommu_ops *iommu_ops_from_fwnode(const struct fwnode_handle *fwnode) +static const struct iommu_device *iommu_from_fwnode(const struct fwnode_handle *fwnode) { - const struct iommu_ops *ops = NULL; - struct iommu_device *iommu; + const struct iommu_device *iommu, *ret = NULL;
spin_lock(&iommu_device_lock); list_for_each_entry(iommu, &iommu_device_list, list) if (iommu->fwnode == fwnode) { - ops = iommu->ops; + ret = iommu; break; } spin_unlock(&iommu_device_lock); - return ops; + return ret; +} + +const struct iommu_ops *iommu_ops_from_fwnode(const struct fwnode_handle *fwnode) +{ + const struct iommu_device *iommu = iommu_from_fwnode(fwnode); + + return iommu ? iommu->ops : NULL; }
int iommu_fwspec_init(struct device *dev, struct fwnode_handle *iommu_fwnode) { - const struct iommu_ops *ops = iommu_ops_from_fwnode(iommu_fwnode); + const struct iommu_device *iommu = iommu_from_fwnode(iommu_fwnode); struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(dev);
- if (!ops) + if (!iommu) return driver_deferred_probe_check_state(dev); + if (!dev->iommu && !READ_ONCE(iommu->ready)) + return -EPROBE_DEFER;
if (fwspec) - return ops == iommu_fwspec_ops(fwspec) ? 0 : -EINVAL; + return iommu->ops == iommu_fwspec_ops(fwspec) ? 0 : -EINVAL;
if (!dev_iommu_get(dev)) return -ENOMEM; --- a/include/linux/iommu.h +++ b/include/linux/iommu.h @@ -735,6 +735,7 @@ struct iommu_domain_ops { * @dev: struct device for sysfs handling * @singleton_group: Used internally for drivers that have only one group * @max_pasids: number of supported PASIDs + * @ready: set once iommu_device_register() has completed successfully */ struct iommu_device { struct list_head list; @@ -743,6 +744,7 @@ struct iommu_device { struct device *dev; struct iommu_group *singleton_group; u32 max_pasids; + bool ready; };
/**