Re: [PATCH v7 1/3] iommufd: Add data structure for Intel VT-d stage-1 cache invalidation

[Nicolin Chen <nicolinc@nvidia.com>]

On Fri, Dec 15, 2023 at 03:04:44AM +0000, Tian, Kevin wrote:
> > From: Nicolin Chen <nicolinc@nvidia.com>
> > Sent: Friday, December 15, 2023 10:28 AM
> > On Fri, Dec 15, 2023 at 01:50:07AM +0000, Tian, Kevin wrote:
> > > > From: Liu, Yi L <yi.l.liu@intel.com>
> > > > Sent: Thursday, December 14, 2023 7:27 PM
> > > >
> > > > On 2023/11/17 21:18, Yi Liu wrote:> This adds the data structure for
> > > > flushing iotlb for the nested domain
> > > >
> > > > +struct iommu_hwpt_vtd_s1_invalidate {
> > > > +     __aligned_u64 addr;
> > > > +     __aligned_u64 npages;
> > > > +     __u32 flags;
> > > > +     __u32 __reserved;
> > > > +     __u32 error;
> > > > +     __u32 dev_id;
> > > > +};
> > > >
> > > > dev_id is used to report the failed device, userspace should be able to
> > map
> > > > it to a vRID, and inject it to VM as part of ITE/ICE error.

> > > and for this error reporting case what we actually require is the
> > > reverse map i.e. pRID->vRID. Not sure whether we can leverage the
> > > same RID mapping uAPI as for ARM/AMD but ignore viommu_id
> > > and then store vRID under device_domain_info. a bit tricky on
> > > life cycle management and also incompatible with SIOV...
> >
> > One thing that I am not very clear here: since both vRID and dev_id
> > are given by the VMM, shouldn't it already know the mapping if the
> > point is to translate (pRID->)dev_id->vRID?
> >
> 
> it's true for current Qemu.
> 
> but there is plan to support Qemu accepting a fd passed by Libvirt.
> In that case Qemu even doesn't see the sysfs path hence is not
> aware of pRID. otherwise yes we could leave the translation to
> VMM instead.

I think I misread Yi's narrative: dev_id is a working approach
for VMM to convert to a vRID, while he is asking for a better
alternative :)