From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jason Gunthorpe <jgg-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
Subject: Re: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and
 allocation APIs
Date: Tue, 6 Apr 2021 09:15:46 -0300
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To: "Tian, Kevin" <kevin.tian-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Cc: "Liu, Yi L" <yi.l.liu-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>, Jean-Philippe Brucker <jean-philippe-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>, Jacob Pan <jacob.jun.pan-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>, LKML <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Joerg Roedel <joro-zLv9SwRftAIdnm+yROfE0A@public.gmane.org>, Lu Baolu <baolu.lu-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>, David Woodhouse <dwmw2-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>, "iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org" <iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org>, "cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" <cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>, Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>, Jean-Philippe Brucker <jean-philippe-68IGFXMjmZ7QT0dZR+AlfA@public.gmane.org>, Alex Williamson <alex.williamson-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Eric Auger <eric.auger-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Jonathan Corbet <corbet-T1hC0tSOHrs@public.gmane.org>, "Raj, Ashok" <ashok.raj-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>, "Wu, Hao" <hao.wu-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>, "Jiang, Dave" <dave.jiang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>

On Tue, Apr 06, 2021 at 12:37:35AM +0000, Tian, Kevin wrote:

> With nested translation it is GVA->GPA->HPA. The kernel needs to
> fix fault related to GPA->HPA (managed by VFIO/VDPA) while 
> handle_mm_fault only handles HVA->HPA. In this case, the 2nd-level
> page fault is expected to be delivered to VFIO/VDPA first which then
> find HVA related to GPA, call handle_mm_fault to fix HVA->HPA,
> and then call iommu_map to fix GPA->HPA in the IOMMU page table.
> This is exactly like how CPU EPT violation is handled.

No, it should all be in the /dev/ioasid layer not duplicated into
every user.

> > If the fault needs to be fixed in the guest, then it needs to be
> > delivered over /dev/ioasid in some way and injected into the
> > vIOMMU. VFIO and VDPA have nothing to do with vIOMMU driver in quemu.
> > 
> > You need to have an interface under /dev/ioasid to create both page
> > table levels and part of that will be to tell the kernel what VA is
> > mapped and how to handle faults.
> 
> VFIO/VDPA already have their own interface to manage GPA->HPA
> mappings. Why do we want to duplicate it in /dev/ioasid? 

They have their own interface to manage other types of HW, we should
not duplicate PASID programming into there too.

Jason