Hi Jean,
Sorry for the late reply, been trying to redesign the notification part.
On Tue, 7 Apr 2020 13:01:07 +0200
Jean-Philippe Brucker <jean-phili...@linaro.org> wrote:
> On Mon, Apr 06, 2020 at 01:02:45PM -0700, Jacob Pan wrote:
> > > > + sdata = kzalloc(sizeof(*sdata), GFP_KERNEL);
> > > > + if (!sdata)
> > > > + return -ENOMEM;
> > >
> > > I don't understand why we need this structure at all, nor why we
> > > need the SID. Users have already allocated an ioasid_set, so why
> > > not just stick the content of ioasid_set_data in there, and pass
> > > the ioasid_set pointer to ioasid_alloc()?
> > >
> >
> > My thinking was that ioasid_set is an opaque user token, e.g. we
> > use mm to identify a common set belong to a VM.
> >
> > This sdata is an IOASID internal structure for managing & servicing
> > per set data. If we let user fill in the content, some of the
> > entries need to be managed by the IOASID code under a lock.
>
> We don't have to let users fill the content. A bit like iommu_domain:
> device drivers don't modify it, they pass it to iommu_map() rather
> than passing a domain ID.
>
much better.
> > IMO, not suitable to let user allocate and manage.
> >
> > Perhaps we should rename struct ioasid_set to ioasid_set_token?
>
> Is the token actually used anywhere? As far as I can tell VFIO does
> its own uniqueness check before calling ioasid_alloc_set(), and
> consumers of notifications don't read the token.
>
for vt-d, the per vm token (preferrably mm) will be used by kvm to
manage its PASID translation table.
when kvm receives a notification about a new guest-host PASID mapping,
it needs to know which vm it belongs to. So if mm is used as token,
both vfio and kvm can identify PASID ownership.
> >
> > /**
> > * struct ioasid_set_data - Meta data about ioasid_set
> > *
> > * @token: Unique to identify an IOASID set
> > * @xa: XArray to store ioasid_set private ID to
> > system-wide IOASID
> > * mapping
> > * @max_id: Max number of IOASIDs can be allocated within
> > the set
> > * @nr_id Number of IOASIDs allocated in the set
> > * @sid ID of the set
> > */
> > struct ioasid_set_data {
> > struct ioasid_set *token;
> > struct xarray xa;
> > int size;
> > int nr_ioasids;
> > int sid;
> > struct rcu_head rcu;
> > };
>
> How about we remove the current ioasid_set, call this structure
> ioasid_set instead of ioasid_set_data, and have ioasid_alloc_set()
> return it, rather than requiring users to allocate the ioasid_set
> themselves?
>
> struct ioasid_set *ioasid_alloc_set(ioasid_t quota):
>
> This way ioasid_set is opaque to users (we could have the definition
> in ioasid.c), but it can be passed to ioasid_alloc() and avoids the
> lookup by SID. Could also add the unique token as a void * argument to
> ioasid_alloc_set(), if needed.
>
Sounds good. still pass a token. Thanks for the idea.
> Thanks,
> Jean
[Jacob Pan]
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