Re: [RFC 04/20] iommu: Add iommu_device_get_info interface

David Gibson
2021-09-29T03:28:13Z

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On Sun, Sep 19, 2021 at 02:38:32PM +0800, Liu Yi L wrote:
> From: Lu Baolu <baolu.lu@linux.intel.com>
>
> This provides an interface for upper layers to get the per-device iommu
> attributes.
>
> int iommu_device_get_info(struct device *dev,
> enum iommu_devattr attr, void *data);

That fact that this interface doesn't let you know how to size the
data buffer, other than by just knowing the right size for each attr
concerns me.

>
> The first attribute (IOMMU_DEV_INFO_FORCE_SNOOP) is added. It tells if
> the iommu can force DMA to snoop cache. At this stage, only PCI devices
> which have this attribute set could use the iommufd, this is due to
> supporting no-snoop DMA requires additional refactoring work on the
> current kvm-vfio contract. The following patch will have vfio check this
> attribute to decide whether a pci device can be exposed through
> /dev/vfio/devices.
>
> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
> ---
> drivers/iommu/iommu.c | 16 ++++++++++++++++
> include/linux/iommu.h | 19 +++++++++++++++++++
> 2 files changed, 35 insertions(+)
>
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 63f0af10c403..5ea3a007fd7c 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -3260,3 +3260,19 @@ static ssize_t iommu_group_store_type(struct iommu_group *group,
>
> return ret;
> }
> +
> +/* Expose per-device iommu attributes. */
> +int iommu_device_get_info(struct device *dev, enum iommu_devattr attr, void *data)
> +{
> + const struct iommu_ops *ops;
> +
> + if (!dev->bus || !dev->bus->iommu_ops)
> + return -EINVAL;
> +
> + ops = dev->bus->iommu_ops;
> + if (unlikely(!ops->device_info))
> + return -ENODEV;
> +
> + return ops->device_info(dev, attr, data);
> +}
> +EXPORT_SYMBOL_GPL(iommu_device_get_info);
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 32d448050bf7..52a6d33c82dc 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -150,6 +150,14 @@ enum iommu_dev_features {
> IOMMU_DEV_FEAT_IOPF,
> };
>
> +/**
> + * enum iommu_devattr - Per device IOMMU attributes
> + * @IOMMU_DEV_INFO_FORCE_SNOOP [bool]: IOMMU can force DMA to be snooped.
> + */
> +enum iommu_devattr {
> + IOMMU_DEV_INFO_FORCE_SNOOP,
> +};
> +
> #define IOMMU_PASID_INVALID (-1U)
>
> #ifdef CONFIG_IOMMU_API
> @@ -215,6 +223,7 @@ struct iommu_iotlb_gather {
> * - IOMMU_DOMAIN_IDENTITY: must use an identity domain
> * - IOMMU_DOMAIN_DMA: must use a dma domain
> * - 0: use the default setting
> + * @device_info: query per-device iommu attributes
> * @pgsize_bitmap: bitmap of all possible supported page sizes
> * @owner: Driver module providing these ops
> */
> @@ -283,6 +292,8 @@ struct iommu_ops {
>
> int (*def_domain_type)(struct device *dev);
>
> + int (*device_info)(struct device *dev, enum iommu_devattr attr, void *data);
> +
> unsigned long pgsize_bitmap;
> struct module *owner;
> };
> @@ -604,6 +615,8 @@ struct iommu_sva *iommu_sva_bind_device(struct device *dev,
> void iommu_sva_unbind_device(struct iommu_sva *handle);
> u32 iommu_sva_get_pasid(struct iommu_sva *handle);
>
> +int iommu_device_get_info(struct device *dev, enum iommu_devattr attr, void *data);
> +
> #else /* CONFIG_IOMMU_API */
>
> struct iommu_ops {};
> @@ -999,6 +1012,12 @@ static inline struct iommu_fwspec *dev_iommu_fwspec_get(struct device *dev)
> {
> return NULL;
> }
> +
> +static inline int iommu_device_get_info(struct device *dev,
> + enum iommu_devattr type, void *data)
> +{
> + return -ENODEV;
> +}
> #endif /* CONFIG_IOMMU_API */
>
> /**

--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson

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