RE: [PATCH v2 00/11] iommufd: Add nesting infrastructure

Tian, Kevin
2023-06-29T02:16:38Z

> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Wednesday, June 28, 2023 8:36 PM
>
> On Wed, Jun 28, 2023 at 02:47:02AM +0000, Tian, Kevin wrote:
> > > From: Jason Gunthorpe <jgg@nvidia.com>
> > > Sent: Wednesday, June 28, 2023 12:01 AM
> > >
> > > On Tue, Jun 27, 2023 at 06:02:13AM +0000, Tian, Kevin wrote:
> > > > > From: Nicolin Chen <nicolinc@nvidia.com>
> > > > > Sent: Tuesday, June 27, 2023 1:29 AM
> > > > >
> > > > > > I'm not sure whether the MSI region needs a special MSI type or
> > > > > > just a general RESV_DIRECT type for 1:1 mapping, though.
> > > > >
> > > > > I don't quite get this part. Isn't MSI having IOMMU_RESV_MSI
> > > > > and IOMMU_RESV_SW_MSI? Or does it juset mean we should report
> > > > > the iommu_resv_type along with reserved regions in new ioctl?
> > > > >
> > > >
> > > > Currently those are iommu internal types. When defining the new
> > > > ioctl we need think about what are necessary presenting to the user.
> > > >
> > > > Probably just a list of reserved regions plus a flag to mark which
> > > > one is SW_MSI? Except SW_MSI all other reserved region types
> > > > just need the user to reserve them w/o knowing more detail.
> > >
> > > I think I prefer the idea we just import the reserved regions from a
> > > devid and do not expose any of this detail to userspace.
> > >
> > > Kernel can make only the SW_MSI a mandatory cut out when the S2 is
> > > attached.
> > >
> >
> > I'm confused.
> >
> > The VMM needs to know reserved regions per dev_id and report them
> > to the guest.
> >
> > And we have aligned on that reserved regions (except SW_MSI) should
> > not be automatically added to S2 in nesting case. Then the VMM cannot
> > rely on IOAS_IOVA_RANGES to identify the reserved regions.
>
> We also said we need a way to load the reserved regions to create an
> identity compatible version of the HWPT
>
> So we have a model where the VMM will want to load in regions beyond
> the currently attached device needs

No question on this.

>
> > So there needs a new interface for the user to discover reserved regions
> > per dev_id, within which the SW_MSI region should be marked out so
> > identity mapping can be installed properly for it in S1.
> >
> > Did I misunderstand your point in previous discussion?
>
> This is another discussion, if the vmm needs this then we probably
> need a new API to get it.
>

Then it's clear. 😊