linux-kernel - RE: [PATCH RFCv1 08/14] iommufd: Add IOMMU_VIOMMU_SET_DEV

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Date: Fri, 7 Jun 2024 00:36:46 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Jason Gunthorpe <jgg@...dia.com>, Nicolin Chen <nicolinc@...dia.com>
CC: "will@...nel.org" <will@...nel.org>, "robin.murphy@....com"
	<robin.murphy@....com>, "suravee.suthikulpanit@....com"
	<suravee.suthikulpanit@....com>, "joro@...tes.org" <joro@...tes.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "linux-tegra@...r.kernel.org"
	<linux-tegra@...r.kernel.org>, "Liu, Yi L" <yi.l.liu@...el.com>,
	"eric.auger@...hat.com" <eric.auger@...hat.com>, "vasant.hegde@....com"
	<vasant.hegde@....com>, "jon.grimm@....com" <jon.grimm@....com>,
	"santosh.shukla@....com" <santosh.shukla@....com>, "Dhaval.Giani@....com"
	<Dhaval.Giani@....com>, "shameerali.kolothum.thodi@...wei.com"
	<shameerali.kolothum.thodi@...wei.com>
Subject: RE: [PATCH RFCv1 08/14] iommufd: Add IOMMU_VIOMMU_SET_DEV_ID ioctl

> From: Jason Gunthorpe <jgg@...dia.com>
> Sent: Friday, June 7, 2024 8:27 AM
> 
> 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?
> 

migration? a single vSMMU provides better compatibility between
src/dest...