Re: [PATCH v3 01/18] iommu: Add device dma ownership set/release interfaces

Joerg Roedel
2021-12-06T13:36:04Z

On Mon, Dec 06, 2021 at 09:58:46AM +0800, Lu Baolu wrote:
> >From the perspective of who is initiating the device to do DMA, device
> DMA could be divided into the following types:
>
> DMA_OWNER_DMA_API: Device DMAs are initiated by a kernel driver
> through the kernel DMA API.
> DMA_OWNER_PRIVATE_DOMAIN: Device DMAs are initiated by a kernel
> driver with its own PRIVATE domain.
> DMA_OWNER_PRIVATE_DOMAIN_USER: Device DMAs are initiated by
> userspace.

I have looked at the other iommu patches in this series, but I still
don't quite get what the difference in the code flow is between
DMA_OWNER_PRIVATE_DOMAIN and DMA_OWNER_PRIVATE_DOMAIN_USER. What are the
differences in the iommu core behavior based on this setting?

> int iommu_device_set_dma_owner(struct device *dev,
> enum iommu_dma_owner type, void *owner_cookie);
> void iommu_device_release_dma_owner(struct device *dev,
> enum iommu_dma_owner type);

It the owner is a group-wide setting, it should be called with the group
instead of the device. I have seen the group-specific funcitons are
added later, but that leaves the question why the device-specific ones
are needed at all.

> + enum iommu_dma_owner dma_owner;
> + refcount_t owner_cnt;
> + void *owner_cookie;
> };

I am also not quite happy yet with calling this dma_owner, but can't
come up with a better name yet.

>
> struct group_device {
> @@ -621,6 +624,7 @@ struct iommu_group *iommu_group_alloc(void)
> INIT_LIST_HEAD(&group->devices);
> INIT_LIST_HEAD(&group->entry);
> BLOCKING_INIT_NOTIFIER_HEAD(&group->notifier);
> + group->dma_owner = DMA_OWNER_NONE;

DMA_OWNER_NONE is also questionable. All devices are always in one
domain, and the default domain is always the one used for DMA-API, so
why isn't the initial value DMA_OWNER_DMA_API?

Regards,

Joerg