Re: [PATCH v2 06/17] iommu: Add iommu_fwspec_alloc/dealloc()

Hector Martin
2023-11-19T08:16:35Z

On 2023/11/15 23:05, Jason Gunthorpe wrote:
> Allow fwspec to exist independently from the dev->iommu by providing
> functions to allow allocating and freeing the raw struct iommu_fwspec.
>
> Reflow the existing paths to call the new alloc/dealloc functions.
>
> Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> ---
> drivers/iommu/iommu.c | 82 ++++++++++++++++++++++++++++++++-----------
> include/linux/iommu.h | 11 +++++-
> 2 files changed, 72 insertions(+), 21 deletions(-)
>
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 18a82a20934d53..86bbb9e75c7e03 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -361,10 +361,8 @@ static void dev_iommu_free(struct device *dev)
> struct dev_iommu *param = dev->iommu;
>
> dev->iommu = NULL;
> - if (param->fwspec) {
> - fwnode_handle_put(param->fwspec->iommu_fwnode);
> - kfree(param->fwspec);
> - }
> + if (param->fwspec)
> + iommu_fwspec_dealloc(param->fwspec);
> kfree(param);
> }
>
> @@ -2920,10 +2918,61 @@ const struct iommu_ops *iommu_ops_from_fwnode(struct fwnode_handle *fwnode)
> return ops;
> }
>
> +static int iommu_fwspec_assign_iommu(struct iommu_fwspec *fwspec,
> + struct device *dev,
> + struct fwnode_handle *iommu_fwnode)
> +{
> + const struct iommu_ops *ops;
> +
> + if (fwspec->iommu_fwnode) {
> + /*
> + * fwspec->iommu_fwnode is the first iommu's fwnode. In the rare
> + * case of multiple iommus for one device they must point to the
> + * same driver, checked via same ops.
> + */
> + ops = iommu_ops_from_fwnode(iommu_fwnode);

This carries over a related bug from the original code: If a device has
two IOMMUs and the first one probes but the second one defers, ops will
be NULL here and the check will fail with EINVAL.

Adding a check for that case here fixes it:

if (!ops)
return driver_deferred_probe_check_state(dev);

With that, for the whole series:

Tested-by: Hector Martin <marcan@marcan.st>

I can't specifically test for the probe races the series intends to fix
though, since that bug we only hit extremely rarely. I'm just testing
that nothing breaks.

> + if (fwspec->ops != ops)
> + return -EINVAL;
> + return 0;
> + }
> +
> + if (!fwspec->ops) {
> + ops = iommu_ops_from_fwnode(iommu_fwnode);
> + if (!ops)
> + return driver_deferred_probe_check_state(dev);
> + fwspec->ops = ops;
> + }
> +
> + of_node_get(to_of_node(iommu_fwnode));
> + fwspec->iommu_fwnode = iommu_fwnode;
> + return 0;
> +}
> +
> +struct iommu_fwspec *iommu_fwspec_alloc(void)
> +{
> + struct iommu_fwspec *fwspec;
> +
> + fwspec = kzalloc(sizeof(*fwspec), GFP_KERNEL);
> + if (!fwspec)
> + return ERR_PTR(-ENOMEM);
> + return fwspec;
> +}
> +
> +void iommu_fwspec_dealloc(struct iommu_fwspec *fwspec)
> +{
> + if (!fwspec)
> + return;
> +
> + if (fwspec->iommu_fwnode)
> + fwnode_handle_put(fwspec->iommu_fwnode);
> + kfree(fwspec);
> +}
> +
> int iommu_fwspec_init(struct device *dev, struct fwnode_handle *iommu_fwnode,
> const struct iommu_ops *ops)
> {
> struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(dev);
> + int ret;
>
> if (fwspec)
> return ops == fwspec->ops ? 0 : -EINVAL;
> @@ -2931,29 +2980,22 @@ int iommu_fwspec_init(struct device *dev, struct fwnode_handle *iommu_fwnode,
> if (!dev_iommu_get(dev))
> return -ENOMEM;
>
> - fwspec = kzalloc(sizeof(*fwspec), GFP_KERNEL);
> - if (!fwspec)
> - return -ENOMEM;
> + fwspec = iommu_fwspec_alloc();
> + if (IS_ERR(fwspec))
> + return PTR_ERR(fwspec);
>
> - of_node_get(to_of_node(iommu_fwnode));
> - fwspec->iommu_fwnode = iommu_fwnode;
> fwspec->ops = ops;
> + ret = iommu_fwspec_assign_iommu(fwspec, dev, iommu_fwnode);
> + if (ret) {
> + iommu_fwspec_dealloc(fwspec);
> + return ret;
> + }
> +
> dev_iommu_fwspec_set(dev, fwspec);
> return 0;
> }
> EXPORT_SYMBOL_GPL(iommu_fwspec_init);
>
> -void iommu_fwspec_free(struct device *dev)
> -{
> - struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(dev);
> -
> - if (fwspec) {
> - fwnode_handle_put(fwspec->iommu_fwnode);
> - kfree(fwspec);
> - dev_iommu_fwspec_set(dev, NULL);
> - }
> -}
> -EXPORT_SYMBOL_GPL(iommu_fwspec_free);
>
> int iommu_fwspec_add_ids(struct device *dev, u32 *ids, int num_ids)
> {
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index e98a4ca8f536b7..c7c68cb59aa4dc 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -813,9 +813,18 @@ struct iommu_sva {
> struct iommu_domain *domain;
> };
>
> +struct iommu_fwspec *iommu_fwspec_alloc(void);
> +void iommu_fwspec_dealloc(struct iommu_fwspec *fwspec);
> +
> int iommu_fwspec_init(struct device *dev, struct fwnode_handle *iommu_fwnode,
> const struct iommu_ops *ops);
> -void iommu_fwspec_free(struct device *dev);
> +static inline void iommu_fwspec_free(struct device *dev)
> +{
> + if (!dev->iommu)
> + return;
> + iommu_fwspec_dealloc(dev->iommu->fwspec);
> + dev->iommu->fwspec = NULL;
> +}
> int iommu_fwspec_add_ids(struct device *dev, u32 *ids, int num_ids);
> const struct iommu_ops *iommu_ops_from_fwnode(struct fwnode_handle *fwnode);
>

- Hector