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Date: Tue, 25 Jan 2022 00:20:26 +0000
From: Robin Murphy <robin.murphy@....com>
To: Lu Baolu <baolu.lu@...ux.intel.com>,
Joerg Roedel <joro@...tes.org>,
Jason Gunthorpe <jgg@...dia.com>,
Christoph Hellwig <hch@...radead.org>,
Ben Skeggs <bskeggs@...hat.com>,
Kevin Tian <kevin.tian@...el.com>,
Ashok Raj <ashok.raj@...el.com>, Will Deacon <will@...nel.org>
Cc: David Airlie <airlied@...ux.ie>, linux-kernel@...r.kernel.org,
iommu@...ts.linux-foundation.org,
Jonathan Hunter <jonathanh@...dia.com>,
Alex Williamson <alex.williamson@...hat.com>,
Thierry Reding <thierry.reding@...il.com>,
Jacob jun Pan <jacob.jun.pan@...el.com>,
Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH 6/7] iommu: Use right way to retrieve iommu_ops
On 2022-01-24 07:11, Lu Baolu wrote:
> The common iommu_ops is hooked to both device and domain. When a helper
> has both device and domain pointer, the way to get the iommu_ops looks
> messy in iommu core. This sorts out the way to get iommu_ops. The device
> related helpers go through device pointer, while the domain related ones
> go through domain pointer.
>
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> ---
> include/linux/iommu.h | 8 ++++++++
> drivers/iommu/iommu.c | 25 ++++++++++++++-----------
> 2 files changed, 22 insertions(+), 11 deletions(-)
>
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index aa5486243892..111b3e9c79bb 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -385,6 +385,14 @@ static inline void iommu_iotlb_gather_init(struct iommu_iotlb_gather *gather)
> };
> }
>
> +static inline const struct iommu_ops *dev_iommu_ops_get(struct device *dev)
> +{
> + if (dev && dev->iommu && dev->iommu->iommu_dev)
> + return dev->iommu->iommu_dev->ops;
> +
> + return NULL;
This probably warrants at least a WARN, but it's arguable to just 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.
> +}
> +
> #define IOMMU_BUS_NOTIFY_PRIORITY 0
> #define IOMMU_GROUP_NOTIFY_ADD_DEVICE 1 /* Device added */
> #define IOMMU_GROUP_NOTIFY_DEL_DEVICE 2 /* Pre Device removed */
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 5230c6d90ece..6631e2ea44df 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -764,6 +764,7 @@ EXPORT_SYMBOL_GPL(iommu_group_set_name);
> static int iommu_create_device_direct_mappings(struct iommu_group *group,
> struct device *dev)
> {
> + const struct iommu_ops *ops = dev_iommu_ops_get(dev);
> struct iommu_domain *domain = group->default_domain;
> struct iommu_resv_region *entry;
> struct list_head mappings;
> @@ -785,8 +786,8 @@ static int iommu_create_device_direct_mappings(struct iommu_group *group,
> dma_addr_t start, end, addr;
> size_t map_size = 0;
>
> - if (domain->ops->apply_resv_region)
> - domain->ops->apply_resv_region(dev, domain, entry);
> + if (ops->apply_resv_region)
> + ops->apply_resv_region(dev, domain, entry);
Strictly I think this was a domain op, as it was about reserving the
IOVA range in the given DMA domain. Also taking the domain as an
argument is a bit of a giveaway. However it's now just dead code either
way since there are no remaining implementations, and no reason for any
new ones.
>
> start = ALIGN(entry->start, pg_size);
> end = ALIGN(entry->start + entry->length, pg_size);
> @@ -831,8 +832,10 @@ static int iommu_create_device_direct_mappings(struct iommu_group *group,
> static bool iommu_is_attach_deferred(struct iommu_domain *domain,
> struct device *dev)
> {
> - if (domain->ops->is_attach_deferred)
> - return domain->ops->is_attach_deferred(domain, dev);
> + const struct iommu_ops *ops = dev_iommu_ops_get(dev);
> +
> + if (ops->is_attach_deferred)
> + return ops->is_attach_deferred(domain, dev);
Similarly if this takes a domain as its first argument then it's de
facto a domain method. However, I'd concur that logically it *is* a
device op, so let's drop that (unused) domain argument if we're cleaning up.
Maybe there's even an argument for factoring this out to a standard flag
in dev_iommu rather than an op at all?
The others covered here look OK - we can blame PCI for page response
being weirdly device-centric - however could we also convert all the
feasible instances of dev->bus->iommu_ops to dev_iommu_ops() as well?
(Subtly implying that I'm also not a fan of having "_get" in the name
for a non-refcounted lookup...) Obviously iommu_probe_device() and
iommmu_domain_alloc() still need bus ops at this point, but I'm working
on that... :)
Thanks,
Robin.
> return false;
> }
> @@ -1251,10 +1254,10 @@ 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_get(dev);
> bool has_pasid = msg->flags & IOMMU_PAGE_RESP_PASID_VALID;
> - struct iommu_domain *domain = iommu_get_domain_for_dev(dev);
>
> - if (!domain || !domain->ops->page_response)
> + if (!ops || !ops->page_response)
> return -ENODEV;
>
> if (!param || !param->fault_param)
> @@ -1295,7 +1298,7 @@ int iommu_page_response(struct device *dev,
> msg->pasid = 0;
> }
>
> - ret = domain->ops->page_response(dev, evt, msg);
> + ret = ops->page_response(dev, evt, msg);
> list_del(&evt->list);
> kfree(evt);
> break;
> @@ -1758,10 +1761,10 @@ static int __iommu_group_dma_attach(struct iommu_group *group)
>
> static int iommu_group_do_probe_finalize(struct device *dev, void *data)
> {
> - struct iommu_domain *domain = data;
> + const struct iommu_ops *ops = dev_iommu_ops_get(dev);
>
> - if (domain->ops->probe_finalize)
> - domain->ops->probe_finalize(dev);
> + if (ops->probe_finalize)
> + ops->probe_finalize(dev);
>
> return 0;
> }
> @@ -2020,7 +2023,7 @@ EXPORT_SYMBOL_GPL(iommu_attach_device);
>
> int iommu_deferred_attach(struct device *dev, struct iommu_domain *domain)
> {
> - const struct iommu_ops *ops = domain->ops;
> + const struct iommu_ops *ops = dev_iommu_ops_get(dev);
>
> if (ops->is_attach_deferred && ops->is_attach_deferred(domain, dev))
> return __iommu_attach_device(domain, dev);
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