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Date: Tue, 25 Jan 2022 11:54:15 +0800
From: Lu Baolu <baolu.lu@...ux.intel.com>
To: Robin Murphy <robin.murphy@....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: baolu.lu@...ux.intel.com, 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 1/25/22 8:20 AM, Robin Murphy wrote:
> 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.
I agree that we could add a WARN() here. The expectation is that every
device going through the IOMMU interfaces or helpers should have been
probed by iommu_probe_device().
>
>> +}
>> +
>> #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.
This callback is a dead code. I will cleanup it.
$ git grep apply_resv_region
drivers/iommu/iommu.c: if (ops->apply_resv_region)
drivers/iommu/iommu.c: ops->apply_resv_region(dev,
domain, entry);
include/linux/iommu.h: * @apply_resv_region: Temporary helper call-back
for iova reserved ranges
include/linux/iommu.h: void (*apply_resv_region)(struct device *dev,
>
>> 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?
Make it part of dev_iommu looks more attractive. Let me check how many
efforts will it take. If a lot of changes required, maybe we can remove
@domain in this series and then switch it to a dev_iommu flag in a
separated series.
>
> 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?
Sure.
> (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 and glad to know that.
>
> Thanks,
> Robin.
Best regards,
baolu
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