Messages in this thread Patch in this message | | | Date | Mon, 30 Jan 2023 12:38:01 -0400 | From | Jason Gunthorpe <> | Subject | Re: [PATCH v2 4/8] iommu: Factor out some helpers |
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On Thu, Jan 26, 2023 at 06:26:19PM +0000, Robin Murphy wrote: > The pattern for picking the first device out of the group list is > repeated a few times now, so it's clearly worth factoring out to hide > the group_device detail from places that don't need to know. Similarly, > the safety check for dev_iommu_ops() at public interfaces starts looking > a bit repetitive, and might not be completely obvious at first glance, > so let's factor that out for clarity as well, in preparation for more > uses of both. > > Signed-off-by: Robin Murphy <robin.murphy@arm.com> > --- > > v2: - Add dev_iommu_ops_valid() helper > - Add lockdep assertion [Jason] > > drivers/iommu/iommu.c | 39 ++++++++++++++++++++++----------------- > 1 file changed, 22 insertions(+), 17 deletions(-) > > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c > index 77f076030995..440bb3b7bded 100644 > --- a/drivers/iommu/iommu.c > +++ b/drivers/iommu/iommu.c > @@ -284,6 +284,12 @@ static void dev_iommu_free(struct device *dev) > kfree(param); > } > > +/* Only needed in public APIs which allow unchecked devices for convenience */ > +static bool dev_iommu_ops_valid(struct device *dev) > +{ > + return dev->iommu && dev->iommu->iommu_dev; > +}
I did an audit and more than half the callers need this test, and a few places are missing it already.
We've kind of made a systematic error that assumes being in a group is sufficient to prove there are non-NULL ops.
So I suggest that we make dev_iommu_ops() return NULL in all cases where there is no driver and have a new API to get the ops in cases where the call chain knows that it is safe, and there are only 5 of those cases.
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c index de91dd88705bd3..4b04ad50de8d6b 100644 --- a/drivers/iommu/iommu.c +++ b/drivers/iommu/iommu.c @@ -98,7 +98,8 @@ static int __iommu_group_set_domain(struct iommu_group *group, struct iommu_domain *new_domain); static int iommu_create_device_direct_mappings(struct iommu_group *group, struct device *dev); -static struct iommu_group *iommu_group_get_for_dev(struct device *dev); +static struct iommu_group *iommu_group_get_for_dev(struct device *dev, + const struct iommu_ops *ops); static ssize_t iommu_group_store_type(struct iommu_group *group, const char *buf, size_t count); @@ -130,6 +131,19 @@ static struct bus_type * const iommu_buses[] = { #endif }; +/* + * This may only be called if it is already clear from the calling context that + * the device has an ops. Seeing the device is part of an iommu_group is not + * enough as VFIO and POWER put devices in iommu_groups and do not attach + * drivers. Thus the only places that are safe have either already called + * dev_iommu_ops() on their call chain, or were responsible for assigning ops in + * the first place. + */ +static inline const struct iommu_ops *dev_iommu_ops_safe(struct device *dev) +{ + return dev->iommu->iommu_dev->ops; +} + /* * Use a function instead of an array here because the domain-type is a * bit-field, so an array would waste memory. @@ -338,7 +352,7 @@ static int __iommu_probe_device(struct device *dev, struct list_head *group_list dev->iommu->iommu_dev = iommu_dev; dev->iommu->max_pasids = dev_iommu_get_max_pasids(dev); - group = iommu_group_get_for_dev(dev); + group = iommu_group_get_for_dev(dev, ops); if (IS_ERR(group)) { ret = PTR_ERR(group); goto out_release; @@ -414,7 +428,8 @@ int iommu_probe_device(struct device *dev) mutex_unlock(&group->mutex); iommu_group_put(group); - ops = dev_iommu_ops(dev); + /* __iommu_probe_device() set the ops */ + ops = dev_iommu_ops_safe(dev); if (ops->probe_finalize) ops->probe_finalize(dev); @@ -430,14 +445,13 @@ int iommu_probe_device(struct device *dev) void iommu_release_device(struct device *dev) { - const struct iommu_ops *ops; + const struct iommu_ops *ops = dev_iommu_ops(dev); - if (!dev->iommu) + if (!ops) return; iommu_device_unlink(dev->iommu->iommu_dev, dev); - ops = dev_iommu_ops(dev); if (ops->release_device) ops->release_device(dev); @@ -614,13 +628,6 @@ int iommu_get_group_resv_regions(struct iommu_group *group, list_for_each_entry(device, &group->devices, list) { struct list_head dev_resv_regions; - /* - * Non-API groups still expose reserved_regions in sysfs, - * so filter out calls that get here that way. - */ - if (!device->dev->iommu) - break; - INIT_LIST_HEAD(&dev_resv_regions); iommu_get_resv_regions(device->dev, &dev_resv_regions); ret = iommu_insert_device_resv_regions(&dev_resv_regions, head); @@ -1332,7 +1339,8 @@ int iommu_page_response(struct device *dev, struct iommu_fault_event *evt; struct iommu_fault_page_request *prm; struct dev_iommu *param = dev->iommu; - const struct iommu_ops *ops = dev_iommu_ops(dev); + /* This API should only be called from an IOMMU driver */ + const struct iommu_ops *ops = dev_iommu_ops_safe(dev); bool has_pasid = msg->flags & IOMMU_PAGE_RESP_PASID_VALID; if (!ops->page_response) @@ -1601,7 +1609,8 @@ EXPORT_SYMBOL_GPL(fsl_mc_device_group); static int iommu_get_def_domain_type(struct device *dev) { - const struct iommu_ops *ops = dev_iommu_ops(dev); + /* It is not locked but all callers know there is an ops */ + const struct iommu_ops *ops = dev_iommu_ops_safe(dev); if (dev_is_pci(dev) && to_pci_dev(dev)->untrusted) return IOMMU_DOMAIN_DMA; @@ -1658,9 +1667,9 @@ static int iommu_alloc_default_domain(struct iommu_group *group, * to the returned IOMMU group, which will already include the provided * device. The reference should be released with iommu_group_put(). */ -static struct iommu_group *iommu_group_get_for_dev(struct device *dev) +static struct iommu_group *iommu_group_get_for_dev(struct device *dev, + const struct iommu_ops *ops) { - const struct iommu_ops *ops = dev_iommu_ops(dev); struct iommu_group *group; int ret; @@ -1795,7 +1804,8 @@ static int __iommu_group_dma_attach(struct iommu_group *group) static int iommu_group_do_probe_finalize(struct device *dev, void *data) { - const struct iommu_ops *ops = dev_iommu_ops(dev); + /* It is unlocked but all callers know there is an ops */ + const struct iommu_ops *ops = dev_iommu_ops_safe(dev); if (ops->probe_finalize) ops->probe_finalize(dev); @@ -1884,13 +1894,9 @@ EXPORT_SYMBOL_GPL(iommu_present); */ bool device_iommu_capable(struct device *dev, enum iommu_cap cap) { - const struct iommu_ops *ops; - - if (!dev->iommu || !dev->iommu->iommu_dev) - return false; + const struct iommu_ops *ops = dev_iommu_ops(dev); - ops = dev_iommu_ops(dev); - if (!ops->capable) + if (!ops || !ops->capable) return false; return ops->capable(dev, cap); @@ -2620,7 +2626,11 @@ void iommu_get_resv_regions(struct device *dev, struct list_head *list) { const struct iommu_ops *ops = dev_iommu_ops(dev); - if (ops->get_resv_regions) + /* + * Non-API groups still expose reserved_regions in sysfs, so filter out + * calls that get here that way. + */ + if (ops && ops->get_resv_regions) ops->get_resv_regions(dev, list); } @@ -2979,6 +2989,11 @@ static ssize_t iommu_group_store_type(struct iommu_group *group, /* Since group has only one device */ grp_dev = list_first_entry(&group->devices, struct group_device, list); dev = grp_dev->dev; + if (!dev_iommu_ops(dev)) { + /* The group doesn't have an iommu driver attached */ + mutex_unlock(&group->mutex); + return -EINVAL; + } get_device(dev); /* @@ -3301,7 +3316,7 @@ static void __iommu_remove_group_pasid(struct iommu_group *group, const struct iommu_ops *ops; list_for_each_entry(device, &group->devices, list) { - ops = dev_iommu_ops(device->dev); + ops = dev_iommu_ops_safe(device->dev); ops->remove_dev_pasid(device->dev, pasid); } } @@ -3413,6 +3428,9 @@ struct iommu_domain *iommu_sva_domain_alloc(struct device *dev, const struct iommu_ops *ops = dev_iommu_ops(dev); struct iommu_domain *domain; + if (!ops) + return NULL; + domain = ops->domain_alloc(IOMMU_DOMAIN_SVA); if (!domain) return NULL; diff --git a/include/linux/iommu.h b/include/linux/iommu.h index 46e1347bfa2286..60e84f8c7c46e9 100644 --- a/include/linux/iommu.h +++ b/include/linux/iommu.h @@ -441,14 +441,11 @@ static inline void iommu_iotlb_gather_init(struct iommu_iotlb_gather *gather) }; } +/* May return NULL if the device has no iommu driver */ static inline const struct iommu_ops *dev_iommu_ops(struct device *dev) { - /* - * Assume that valid ops must be installed if iommu_probe_device() - * has succeeded. The device ops are essentially for internal use - * within the IOMMU subsystem itself, so we should be able to trust - * ourselves not to misuse the helper. - */ + if (!dev->iommu) + return NULL; return dev->iommu->iommu_dev->ops; }
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