Re: [PATCH v6 03/10] iommu: Add attach handle to struct iopf_group

[Baolu Lu]

On 6/5/24 4:23 PM, Tian, Kevin wrote:
> > From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > Sent: Monday, May 27, 2024 12:05 PM
> >
> > @@ -249,6 +249,12 @@ enum iommu_cap {
> >   	 */
> >   	IOMMU_CAP_DEFERRED_FLUSH,
> >   	IOMMU_CAP_DIRTY_TRACKING,	/* IOMMU supports dirty
> > tracking */
> > +	/*
> > +	 * IOMMU driver supports user-managed IOASID table. There is no
> > +	 * user domain for each PASID and the I/O page faults are forwarded
> > +	 * through the user domain attached to the device RID.
> > +	 */
> > +	IOMMU_CAP_USER_IOASID_TABLE,
> >   };
>
> Given all other context are around PASID let's just call it as USER_PASID_TABLE.
>
> btw this goes differently from your plan in [1] which tried to introduce
> different nesting types between Intel and other vendors.
>
> I guess the reason might be that you want to avoid getting the handle
> for RID on Intel platform in case of failing to find the handle for the
> faulting PASID. and save a new domain type.
>
> this looks fine to me but should be explained.

Yeah! I was considering this in two aspects and chose this simple
solution in the end.

- If we choose to add a new domain type, we need to change iommufd,
  iommu core and the individual driver. That seems too complicated to
  address a small issue here.

- Fundamentally, this is a hardware implementation difference, hence use
  the existing per-device iommu capability interface sounds more
  reasonable.

> [1] https://lore.kernel.org/linux-iommu/0de7c71f-571a-4800-8f2b-9eda0c6b75de@xxxxxxxxxxxxxxx/

Best regards,
baolu