linux-kernel - Re: [RFC PATCH 3/6] iommu/amd: Introduce Guest-ID struct amd_iommu

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Date: Fri, 5 Jan 2024 10:38:11 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: "Suthikulpanit, Suravee" <suravee.suthikulpanit@....com>
Cc: "Tian, Kevin" <kevin.tian@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	"joro@...tes.org" <joro@...tes.org>,
	"Liu, Yi L" <yi.l.liu@...el.com>,
	"nicolinc@...dia.com" <nicolinc@...dia.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>,
	"pandoh@...gle.com" <pandoh@...gle.com>,
	"loganodell@...gle.com" <loganodell@...gle.com>
Subject: Re: [RFC PATCH 3/6] iommu/amd: Introduce Guest-ID struct
 amd_iommu_vminfo

On Fri, Jan 05, 2024 at 08:39:56PM +0700, Suthikulpanit, Suravee wrote:
> Hi Kevin
> 
> On 12/15/2023 2:35 PM, Tian, Kevin wrote:
> > > From: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
> > > Sent: Wednesday, December 13, 2023 12:02 AM
> > > 
> > > AMD HW-vIOMMU feature requires IOMMU driver to specify a unique 16-bit
> > > Guest ID (GID) for each VM. This ID is used to index into various
> > > data structures for configuring the hardware.
> > > 
> > > Introduce amd_iommu_vminfo_hash hashtable to store per-vm
> > > configuration,
> > > which uses 16-bit GID as a hash key along with helper functions.
> > > 
> > 
> > somehow it's unclear to me whether this series is only for hw
> > supporting vf or broader hw supporting nested capability. for
> > the latter case is GID still necessary?
> 
> I am restructuring the series and might be moving GID stuff until later when
> introduce broader hw support for AMD vIOMMU.

I'm hoping you can just skip enabling the viommu features and still
have nesting? That should be OK right? The SW will manage the
invalidations.

I'd like to do ARM and AMD accelerated viommu nesting together since
they are so similar it will help to make the APIs correct.

Jason