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Date: Thu, 6 Jun 2024 21:27:07 -0300
From: Jason Gunthorpe <jgg@nvidia.com>
To: Nicolin Chen <nicolinc@nvidia.com>
Cc: "Tian, Kevin" <kevin.tian@intel.com>,
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Subject: Re: [PATCH RFCv1 08/14] iommufd: Add IOMMU_VIOMMU_SET_DEV_ID ioctl
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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