Re: [PATCH v3 23/25] iommu: Add ops->domain_alloc_paging()

[Baolu Lu <baolu.lu@linux.intel.com>]

On 6/10/23 3:56 AM, Jason Gunthorpe wrote:
> This callback requests the driver to create only a __IOMMU_DOMAIN_PAGING
> domain, so it saves a few lines in a lot of drivers needlessly checking
> the type.
> 
> More critically, this allows us to sweep out all the
> IOMMU_DOMAIN_UNMANAGED and IOMMU_DOMAIN_DMA checks from a lot of the
> drivers, simplifying what is going on in the code and ultimately removing
> the now-unused special cases in drivers where they did not support
> IOMMU_DOMAIN_DMA.
> 
> domain_alloc_paging() should return a struct iommu_domain that is
> functionally compatible with ARM_DMA_USE_IOMMU, dma-iommu.c and iommufd.
> 
> Be forwards looking and pass in a 'struct device *' argument. We can
> provide this when allocating the default_domain. No drivers will look at
> this.

I like this idea. :-)

> 
> Tested-by: Steven Price <steven.price@arm.com>
> Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
> Tested-by: Nicolin Chen <nicolinc@nvidia.com>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> ---
>   drivers/iommu/iommu.c | 13 ++++++++++---
>   include/linux/iommu.h |  3 +++
>   2 files changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 0346c05e108438..2cf523ff9c6f55 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -1985,6 +1985,7 @@ void iommu_set_fault_handler(struct iommu_domain *domain,
>   EXPORT_SYMBOL_GPL(iommu_set_fault_handler);
>   
>   static struct iommu_domain *__iommu_domain_alloc(const struct iommu_ops *ops,
> +						 struct device *dev,
>   						 unsigned int type)
>   {
>   	struct iommu_domain *domain;
> @@ -1992,8 +1993,13 @@ static struct iommu_domain *__iommu_domain_alloc(const struct iommu_ops *ops,
>   
>   	if (alloc_type == IOMMU_DOMAIN_IDENTITY && ops->identity_domain)
>   		return ops->identity_domain;
> +	else if (type & __IOMMU_DOMAIN_PAGING) {
> +		domain = ops->domain_alloc_paging(dev);

This might be problematic because not all IOMMU drivers implement this
callback now. In the missing cases, the code will always result in a
null pointer reference issue?

> +	} else if (ops->domain_alloc)
> +		domain = ops->domain_alloc(alloc_type);
> +	else
> +		return NULL;
>   
> -	domain = ops->domain_alloc(alloc_type);
>   	if (!domain)
>   		return NULL;
>   
> @@ -2024,14 +2030,15 @@ __iommu_group_domain_alloc(struct iommu_group *group, unsigned int type)
>   
>   	lockdep_assert_held(&group->mutex);
>   
> -	return __iommu_domain_alloc(dev_iommu_ops(dev), type);
> +	return __iommu_domain_alloc(dev_iommu_ops(dev), dev, type);
>   }
>   
>   struct iommu_domain *iommu_domain_alloc(const struct bus_type *bus)
>   {
>   	if (bus == NULL || bus->iommu_ops == NULL)
>   		return NULL;
> -	return __iommu_domain_alloc(bus->iommu_ops, IOMMU_DOMAIN_UNMANAGED);
> +	return __iommu_domain_alloc(bus->iommu_ops, NULL,
> +				    IOMMU_DOMAIN_UNMANAGED);

Suppose that iommu_domain_alloc() is always called from device drivers
where device pointer is always available. Is it possible to convert it
to a real device pointer?

>   }
>   EXPORT_SYMBOL_GPL(iommu_domain_alloc);
>   
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 49331573f1d1f5..8e4d178c49c417 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -233,6 +233,8 @@ struct iommu_iotlb_gather {
>    * struct iommu_ops - iommu ops and capabilities
>    * @capable: check capability
>    * @domain_alloc: allocate iommu domain
> + * @domain_alloc_paging: Allocate an iommu_domain that can be used for
> + *                       UNMANAGED, DMA, and DMA_FQ domain types.
>    * @probe_device: Add device to iommu driver handling
>    * @release_device: Remove device from iommu driver handling
>    * @probe_finalize: Do final setup work after the device is added to an IOMMU
> @@ -264,6 +266,7 @@ struct iommu_ops {
>   
>   	/* Domain allocation and freeing by the iommu driver */
>   	struct iommu_domain *(*domain_alloc)(unsigned iommu_domain_type);
> +	struct iommu_domain *(*domain_alloc_paging)(struct device *dev);
>   
>   	struct iommu_device *(*probe_device)(struct device *dev);
>   	void (*release_device)(struct device *dev);

Best regards,
baolu