Re: [PATCH v4 1/6] iommu: Add a per domain PASID for DMA API

Jacob Pan
2022-05-24T15:13:38Z

Hi Jason,

On Tue, 24 May 2022 10:50:34 -0300, Jason Gunthorpe <jgg@nvidia.com> wrote:

> On Wed, May 18, 2022 at 11:21:15AM -0700, Jacob Pan wrote:
> > DMA requests tagged with PASID can target individual IOMMU domains.
> > Introduce a domain-wide PASID for DMA API, it will be used on the same
> > mapping as legacy DMA without PASID. Let it be IOVA or PA in case of
> > identity domain.
>
> Huh? I can't understand what this is trying to say or why this patch
> makes sense.
>
> We really should not have pasid's like this attached to the domains..
>
This is the same "DMA API global PASID" you reviewed in v3, I just
singled it out as a standalone patch and renamed it. Here is your previous
review comment.

> +++ b/include/linux/iommu.h
> @@ -105,6 +105,8 @@ struct iommu_domain {
> enum iommu_page_response_code (*iopf_handler)(struct iommu_fault *fault,
> void *data);
> void *fault_data;
> + ioasid_t pasid; /* Used for DMA requests with PASID */
> + atomic_t pasid_users;

These are poorly named, this is really the DMA API global PASID and
shouldn't be used for other things.

Perhaps I misunderstood, do you mind explaining more?

Thanks,

Jacob