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

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Date: Thu, 14 Dec 2023 19:32:40 -0800
From: Nicolin Chen <nicolinc@...dia.com>
To: "Tian, Kevin" <kevin.tian@...el.com>
CC: "Liu, Yi L" <yi.l.liu@...el.com>, "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>,
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	<shameerali.kolothum.thodi@...wei.com>, "lulu@...hat.com" <lulu@...hat.com>,
	"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

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:> This adds the data structure for
> > > > flushing iotlb for the nested domain
> > > >
> > > > +struct iommu_hwpt_vtd_s1_invalidate {
> > > > +     __aligned_u64 addr;
> > > > +     __aligned_u64 npages;
> > > > +     __u32 flags;
> > > > +     __u32 __reserved;
> > > > +     __u32 error;
> > > > +     __u32 dev_id;
> > > > +};
> > > >
> > > > dev_id is used to report the failed device, userspace should be able to
> > map
> > > > it to a vRID, and inject it to VM as part of ITE/ICE error.

> > > 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 :)