Re: [PATCH 6/7] iommu: Use right way to retrieve iommu_ops

[Lu Baolu]

On 1/25/22 1:36 AM, Jason Gunthorpe wrote:
> On Mon, Jan 24, 2022 at 03:11:01PM +0800, 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@xxxxxxxxxxxxxxx>
> >   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
> > +++ 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;
>
> What is the purpose of this helper?

Get the iommu_ops from a device pointer. Just want to avoid duplicate
code in various functions.

> > +	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);
>
> Here we call it and don't check for NULL? So why did we check the
> interior pointers in the helper?

Yes. Should check.

> > @@ -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);
>
> Same here, at least return false if ops is null..

Yes.

>    
> > @@ -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;
>
> Feels weird that page_response is not connected to a domain, the fault
> originated from a domain after all. I would say this op should be
> moved to the domain and the caller should provide the a pointer to the
> domain that originated the fault.
>
> Ideally since only some domain's will be configured to handle faults
> at all - domains that can't do this should have a NULL page_response
> op, even if other domains created by the same device driver could
> handle page_response..
>
> > @@ -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);
>
> This is an oddball one too, it is finishing setting up the default
> domain for a device? Several drivers seem to recover the default
> domain in their implementations..

In order to avoid default domain type (DMA or IDENDITY) conflict among
devices in a same iommu_group, the probe process is divided into two
phases, one for determining the default domain type and the other for
allocating the default domain and attaching it to the device.

ops->probe_finalize() is called to tell the vendor iommu driver that
the device probe is done. Normally the vendor iommu driver could set the
dma ops in this callback.

> Jason

Best regards,
baolu