Re: [PATCH v2 3/8] iommu/vt-d: Implement device_pasid domain attach ops

Jacob Pan
2022-03-28T22:08:13Z

Hi Kevin,

On Fri, 18 Mar 2022 05:33:38 +0000, "Tian, Kevin" <kevin.tian@intel.com>
wrote:

> > From: Jacob Pan
> > Sent: Thursday, March 17, 2022 5:02 AM
> >
> > Hi Kevin,
> >
> > On Wed, 16 Mar 2022 07:41:34 +0000, "Tian, Kevin" <kevin.tian@intel.com>
> > wrote:
> >
> > > > From: Jason Gunthorpe <jgg@nvidia.com>
> > > > Sent: Tuesday, March 15, 2022 10:33 PM
> > > >
> > > > On Mon, Mar 14, 2022 at 10:07:07PM -0700, Jacob Pan wrote:
> > > > > + /*
> > > > > + * Each domain could have multiple devices attached with
> > > > > shared or
> > > > per
> > > > > + * device PASIDs. At the domain level, we keep track of
> > > > > unique PASIDs
> > > > and
> > > > > + * device user count.
> > > > > + * E.g. If a domain has two devices attached, device A
> > > > > has PASID 0, 1;
> > > > > + * device B has PASID 0, 2. Then the domain would have
> > > > > PASID 0, 1, 2.
> > > > > + */
> > > >
> > > > A 2d array of xarray's seems like a poor data structure for this
> > > > task.
> > >
> > Perhaps i mis-presented here, I am not using 2D array. It is an 1D
> > xarray for domain PASIDs only. Then I use the existing device list in
> > each domain, adding another xa to track per-device-domain PASIDs.
> > > besides that it also doesn't work when we support per-device PASID
> > > allocation in the future. In that case merging device PASIDs together
> > > is conceptually wrong.
> > >
> > Sorry, could you elaborate? If we do per-dev PASID allocation, we could
> > use the ioasid_set for each pdev, right?
>
> My point is simply about the comment above which says the domain
> will have PASID 0, 1, 2 when there is [devA, PASID0] and [devB, PASID0].
> You can maintain a single PASID list only when it's globally allocated
> cross devices. otherwise this has to be a tuple including device and
> PASID.
>
Got you, you are right we don't want to limit to globally allocated scheme.

Thanks,

Jacob