On 2021-02-12 17:28, Shameerali Kolothum Thodi wrote:
-----Original Message----- From: Shameerali Kolothum Thodi Sent: 12 February 2021 16:45 To: 'Robin Murphy' robin.murphy@arm.com; linux-kernel@vger.kernel.org; iommu@lists.linux-foundation.org Cc: joro@8bytes.org; jean-philippe@linaro.org; will@kernel.org; Zengtao (B) prime.zeng@hisilicon.com; linuxarm@openeuler.org Subject: RE: [PATCH v2] iommu: Check dev->iommu in iommu_dev_xxx functions
-----Original Message----- From: Robin Murphy [mailto:robin.murphy@arm.com] Sent: 12 February 2021 16:39 To: Shameerali Kolothum Thodi shameerali.kolothum.thodi@huawei.com; linux-kernel@vger.kernel.org; iommu@lists.linux-foundation.org Cc: joro@8bytes.org; jean-philippe@linaro.org; will@kernel.org; Zengtao (B) prime.zeng@hisilicon.com; linuxarm@openeuler.org Subject: Re: [PATCH v2] iommu: Check dev->iommu in iommu_dev_xxx
functions
On 2021-02-12 14:54, Shameerali Kolothum Thodi wrote:
Hi Robin/Joerg,
-----Original Message----- From: Shameer Kolothum
[mailto:shameerali.kolothum.thodi@huawei.com]
Sent: 01 February 2021 12:41 To: linux-kernel@vger.kernel.org; iommu@lists.linux-foundation.org Cc: joro@8bytes.org; robin.murphy@arm.com; jean-philippe@linaro.org; will@kernel.org; Zengtao (B) prime.zeng@hisilicon.com; linuxarm@openeuler.org Subject: [Linuxarm] [PATCH v2] iommu: Check dev->iommu in
iommu_dev_xxx
functions
The device iommu probe/attach might have failed leaving dev->iommu to NULL and device drivers may still invoke these functions resulting in a crash in iommu vendor driver code. Hence make sure we check that.
Also added iommu_ops to the "struct dev_iommu" and set it if the dev is successfully associated with an iommu.
Fixes: a3a195929d40 ("iommu: Add APIs for multiple domains per
device")
Signed-off-by: Shameer Kolothum
shameerali.kolothum.thodi@huawei.com
v1 --> v2: -Added iommu_ops to struct dev_iommu based on the discussion with
Robin.
-Rebased against iommu-tree core branch.
A gentle ping on this...
Is there a convincing justification for maintaining yet another copy of the ops pointer rather than simply dereferencing iommu_dev->ops at point of use?
TBH, nothing I can think of now. That was mainly the way I interpreted your suggestion from the v1. Now it looks like you didn’t mean it :). I am Ok to rework it to dereference it from iommu_dev. Please let me know.
So we can do something like this,
index fd76e2f579fe..5fd31a3cec18 100644 --- a/drivers/iommu/iommu.c +++ b/drivers/iommu/iommu.c @@ -2865,10 +2865,12 @@ EXPORT_SYMBOL_GPL(iommu_fwspec_add_ids); */ int iommu_dev_enable_feature(struct device *dev, enum iommu_dev_features feat) {
const struct iommu_ops *ops = dev->bus->iommu_ops;
if (dev->iommu && dev->iommu->iommu_dev && dev->iommu->iommu_dev->ops)struct iommu_ops *ops = dev->iommu->iommu_dev->ops;
if (ops && ops->dev_enable_feat)return ops->dev_enable_feat(dev, feat);
if (ops->dev_enable_feat)return ops->dev_enable_feat(dev, feat);} return -ENODEV;}
Again, not sure we need to do the checking for iommu->dev and ops here. If the dev->iommu is set, is it safe to assume that we have a valid iommu->iommu_dev and ops always? (May be it is safer to do the checking in case something else breaks this assumption in future). Please let me know your thoughts.
I think it *could* happen that dev->iommu is set by iommu_fwspec_init() but iommu_probe_device() later refuses the device for whatever reason, so we would still need to check iommu->iommu_dev to be completely safe. We can assume iommu_dev->ops is valid, since if the IOMMU driver has returned something bogus from .probe_device then it's a major bug in that driver and crashing is the best indicator :)
Robin.
Thanks, Shameer
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