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Message-ID: <8f2dd843-a0c5-79d7-f563-f683d460b3df@arm.com>
Date: Fri, 4 Aug 2017 15:44:53 +0100
From: Robin Murphy <robin.murphy@....com>
To: joro@...tes.org
Cc: iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
sudeep.holla@....com
Subject: Re: [PATCH] iommu/of: Fix of_iommu_configure() for disabled IOMMUs
On 04/08/17 12:16, Robin Murphy wrote:
> Sudeep reports that the logic is slightly broken when a PCI iommu-map
> entry targets an IOMMU marked as disabled in DT, since of_pci_map_rid()
> succeeds in following a phandle, and of_iommu_xlate() doesn't return an
> error value, but we miss checking whether ops was actually non-NULL.
> Whilst this could be solved with a point fix in of_pci_iommu_init(), it
> suggests that all the juggling of ERR_PTR values through the ops pointer
> is proving rather too complicated for its own good, so let's instead
> simplify the whole flow (with a side-effect of eliminating the cause of
> the bug).
>
> The fact that we now rely on iommu_fwspec means that we no longer need
> to pass around an iommu_ops pointer at all - we can simply propagate a
> regular int return value until we know whether we have a viable IOMMU,
> then retrieve the ops from the fwspec if and when we actually need them.
> This makes everything a bit more uniform and certainly easier to follow.
>
> Reported-by: Sudeep Holla <sudeep.holla@....com>
> Signed-off-by: Robin Murphy <robin.murphy@....com>
> ---
>
> This could be squashed into the currently-queued offender, but if not,
> Fixes: d87beb749281 ("iommu/of: Handle PCI aliases properly")
>
> Robin.
>
> drivers/iommu/of_iommu.c | 63 ++++++++++++++++++++++++------------------------
> 1 file changed, 31 insertions(+), 32 deletions(-)
>
> diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
> index be8ac1ddec06..198ef9a49f64 100644
> --- a/drivers/iommu/of_iommu.c
> +++ b/drivers/iommu/of_iommu.c
> @@ -25,6 +25,8 @@
> #include <linux/of_pci.h>
> #include <linux/slab.h>
>
> +#define NO_IOMMU 1
> +
> static const struct of_device_id __iommu_of_table_sentinel
> __used __section(__iommu_of_table_end);
>
> @@ -109,8 +111,8 @@ static bool of_iommu_driver_present(struct device_node *np)
> return of_match_node(&__iommu_of_table, np);
> }
>
> -static const struct iommu_ops
> -*of_iommu_xlate(struct device *dev, struct of_phandle_args *iommu_spec)
> +static int of_iommu_xlate(struct device *dev,
> + struct of_phandle_args *iommu_spec)
> {
> const struct iommu_ops *ops;
> struct fwnode_handle *fwnode = &iommu_spec->np->fwnode;
> @@ -120,24 +122,20 @@ static const struct iommu_ops
> if ((ops && !ops->of_xlate) ||
> !of_device_is_available(iommu_spec->np) ||
> (!ops && !of_iommu_driver_present(iommu_spec->np)))
> - return NULL;
> + return NO_IOMMU;
>
> err = iommu_fwspec_init(dev, &iommu_spec->np->fwnode, ops);
> if (err)
> - return ERR_PTR(err);
> + return err;
> /*
> * The otherwise-empty fwspec handily serves to indicate the specific
> * IOMMU device we're waiting for, which will be useful if we ever get
> * a proper probe-ordering dependency mechanism in future.
> */
> if (!ops)
> - return ERR_PTR(-EPROBE_DEFER);
> + return -EPROBE_DEFER;
>
> - err = ops->of_xlate(dev, iommu_spec);
> - if (err)
> - return ERR_PTR(err);
> -
> - return ops;
> + return ops->of_xlate(dev, iommu_spec);
> }
>
> struct of_pci_iommu_alias_info {
> @@ -148,7 +146,6 @@ struct of_pci_iommu_alias_info {
> static int of_pci_iommu_init(struct pci_dev *pdev, u16 alias, void *data)
> {
> struct of_pci_iommu_alias_info *info = data;
> - const struct iommu_ops *ops;
> struct of_phandle_args iommu_spec = { .args_count = 1 };
> int err;
>
> @@ -156,13 +153,12 @@ static int of_pci_iommu_init(struct pci_dev *pdev, u16 alias, void *data)
> "iommu-map-mask", &iommu_spec.np,
> iommu_spec.args);
> if (err)
> - return err == -ENODEV ? 1 : err;
> + return err == -ENODEV ? NO_IOMMU : err;
>
> - ops = of_iommu_xlate(info->dev, &iommu_spec);
> + err = of_iommu_xlate(info->dev, &iommu_spec);
> of_node_put(iommu_spec.np);
> -
> - if (IS_ERR(ops))
> - return PTR_ERR(ops);
> + if (err)
> + return err;
>
> return info->np == pdev->bus->dev.of_node;
> }
> @@ -170,9 +166,9 @@ static int of_pci_iommu_init(struct pci_dev *pdev, u16 alias, void *data)
> const struct iommu_ops *of_iommu_configure(struct device *dev,
> struct device_node *master_np)
> {
> - const struct iommu_ops *ops = NULL;
> + const struct iommu_ops *ops;
> struct iommu_fwspec *fwspec = dev->iommu_fwspec;
> - int err;
> + int err = NO_IOMMU;
>
> if (!master_np)
> return NULL;
> @@ -198,10 +194,6 @@ const struct iommu_ops *of_iommu_configure(struct device *dev,
>
> err = pci_for_each_dma_alias(to_pci_dev(dev),
> of_pci_iommu_init, &info);
> - if (err) /* err > 0 means the walk stopped, but non-fatally */
> - ops = ERR_PTR(min(err, 0));
> - else /* success implies both fwspec and ops are now valid */
> - ops = dev->iommu_fwspec->ops;
> } else {
> struct of_phandle_args iommu_spec;
> int idx = 0;
> @@ -209,28 +201,35 @@ const struct iommu_ops *of_iommu_configure(struct device *dev,
> while (!of_parse_phandle_with_args(master_np, "iommus",
> "#iommu-cells",
> idx, &iommu_spec)) {
> - ops = of_iommu_xlate(dev, &iommu_spec);
> + err = of_iommu_xlate(dev, &iommu_spec);
> of_node_put(iommu_spec.np);
> idx++;
> - if (IS_ERR_OR_NULL(ops))
> + if (err)
> break;
> }
> }
> +
> + /*
> + * Two success conditions are represented by non-negative err here:
> + * >0 : there is no IOMMU, or one was unavailable for non-fatal reasons
> + * 0 : we found an IOMMU, and dev->fwspec is initialised appropriately
> + * <0 : any actual error
> + */
> + if (err > 0)
> + return NULL;
> +
> /*
> * If we have reason to believe the IOMMU driver missed the initial
> * add_device callback for dev, replay it to get things in order.
> */
> - if (!IS_ERR_OR_NULL(ops) && ops->add_device &&
> - dev->bus && !dev->iommu_group) {
> + ops = dev->iommu_fwspec->ops;
> + if (!err && ops->add_device && dev->bus && !dev->iommu_group)
> err = ops->add_device(dev);
> - if (err)
> - ops = ERR_PTR(err);
> - }
>
> /* Ignore all other errors apart from EPROBE_DEFER */
> - if (IS_ERR(ops) && (PTR_ERR(ops) != -EPROBE_DEFER)) {
> - dev_dbg(dev, "Adding to IOMMU failed: %ld\n", PTR_ERR(ops));
> - ops = NULL;
> + if (err && err != -EPROBE_DEFER) {
> + dev_dbg(dev, "Adding to IOMMU failed: %d\n", err);
> + return NULL;
> }
Ugh, no, now we fail to pass -EPROBE_DEFER properly (turns out my test
device was also deferring for other reasons and getting lucky). I really
am starting to hate ERR_PTRs...
v2 coming shortly, sorry.
Robin.
>
> return ops;
>
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