Re: [PATCH RFCv1 08/14] iommufd: Add IOMMU_VIOMMU_SET_DEV_ID ioctl

Jason Gunthorpe
2024-06-07T00:27:11Z

On Thu, Jun 06, 2024 at 11:44:58AM -0700, Nicolin Chen wrote:
> On Thu, Jun 06, 2024 at 03:24:23PM -0300, Jason Gunthorpe wrote:
> > On Sun, Jun 02, 2024 at 08:25:34PM -0700, Nicolin Chen wrote:
> >
> > > > I understand the appeal of doing this has been to minimize qemu
> > > > changes in its ACPI parts if we tackle that instead maybe we should
> > > > just not implement viommu to multiple piommu. It is somewhat
> > > > complicated.
> > >
> > > Would you please clarify that suggestion "not implement viommu
> > > to multiple piommu"?
> > >
> > > For regular nesting (SMMU), we are still doing one vSMMU in the
> > > VMM, though VCMDQ case would be an exception....
> >
> > This is what I mean, always do multiple vSMMU if there are multiple
> > physical pSMMUs. Don't replicate any virtual commands across pSMMUs.
>
> Thanks for clarifying. That also means you'd prefer putting the
> command dispatcher in VMM, which is what we have at this moment.

Unless someone knows a reason why we should strive hard to have only a
single vSMMU and accept some invalidation inefficiency?

Jason