linux-kernel - RE: [PATCH v7 1/3] iommufd: Add data structure for Intel VT-d stage-1 cache invalidation

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Date: Sun, 17 Dec 2023 23:28:24 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Nicolin Chen <nicolinc@...dia.com>, "Liu, Yi L" <yi.l.liu@...el.com>
CC: "joro@...tes.org" <joro@...tes.org>, "alex.williamson@...hat.com"
	<alex.williamson@...hat.com>, "jgg@...dia.com" <jgg@...dia.com>,
	"robin.murphy@....com" <robin.murphy@....com>, "baolu.lu@...ux.intel.com"
	<baolu.lu@...ux.intel.com>, "cohuck@...hat.com" <cohuck@...hat.com>,
	"eric.auger@...hat.com" <eric.auger@...hat.com>, "kvm@...r.kernel.org"
	<kvm@...r.kernel.org>, "mjrosato@...ux.ibm.com" <mjrosato@...ux.ibm.com>,
	"chao.p.peng@...ux.intel.com" <chao.p.peng@...ux.intel.com>,
	"yi.y.sun@...ux.intel.com" <yi.y.sun@...ux.intel.com>, "peterx@...hat.com"
	<peterx@...hat.com>, "jasowang@...hat.com" <jasowang@...hat.com>,
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	"suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>, "Duan,
 Zhenzhong" <zhenzhong.duan@...el.com>, "joao.m.martins@...cle.com"
	<joao.m.martins@...cle.com>, "Zeng, Xin" <xin.zeng@...el.com>, "Zhao, Yan Y"
	<yan.y.zhao@...el.com>
Subject: RE: [PATCH v7 1/3] iommufd: Add data structure for Intel VT-d stage-1
 cache invalidation

> From: Nicolin Chen <nicolinc@...dia.com>
> Sent: Sunday, December 17, 2023 2:49 AM
> 
> On Fri, Dec 15, 2023 at 12:01:19PM +0800, Yi Liu wrote:
> > On 2023/12/15 11:32, Nicolin Chen wrote:
> > > On Fri, Dec 15, 2023 at 03:04:44AM +0000, Tian, Kevin wrote:
> > > > > From: Nicolin Chen <nicolinc@...dia.com>
> > > > > Sent: Friday, December 15, 2023 10:28 AM
> > > > > On Fri, Dec 15, 2023 at 01:50:07AM +0000, Tian, Kevin wrote:
> > > > > > > From: Liu, Yi L <yi.l.liu@...el.com>
> > > > > > > Sent: Thursday, December 14, 2023 7:27 PM
> > > > > > >
> > > > > > > On 2023/11/17 21:18, Yi Liu wrote:
> > > > > > and for this error reporting case what we actually require is the
> > > > > > reverse map i.e. pRID->vRID. Not sure whether we can leverage the
> > > > > > same RID mapping uAPI as for ARM/AMD but ignore viommu_id
> > > > > > and then store vRID under device_domain_info. a bit tricky on
> > > > > > life cycle management and also incompatible with SIOV...
> > > > >
> > > > > One thing that I am not very clear here: since both vRID and dev_id
> > > > > are given by the VMM, shouldn't it already know the mapping if the
> > > > > point is to translate (pRID->)dev_id->vRID?
> > > > >
> > > >
> > > > it's true for current Qemu.
> > > >
> > > > but there is plan to support Qemu accepting a fd passed by Libvirt.
> > > > In that case Qemu even doesn't see the sysfs path hence is not
> > > > aware of pRID. otherwise yes we could leave the translation to
> > > > VMM instead.
> > >
> > > I think I misread Yi's narrative: dev_id is a working approach
> > > for VMM to convert to a vRID, while he is asking for a better
> > > alternative :)
> >
> > In concept, dev_id works, but in reality we have problem to get a dev_id
> > for a given device in intel iommu driver, hence I'm asking for help here. :)
> 
> Yea, I got that.
> 
> Would it be possible for us to postpone this error report in the
> vtd driver?
> 

that is the plan. We'll still report error code but no dev_id error
data. this is allowed by vtd spec.