linux-kernel - Re: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and allocation APIs

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Message-ID: <20210401134236.GF1463678@nvidia.com>
Date:   Thu, 1 Apr 2021 10:42:36 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Liu, Yi L" <yi.l.liu@...el.com>
Cc:     Jean-Philippe Brucker <jean-philippe@...aro.org>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        David Woodhouse <dwmw2@...radead.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        Tejun Heo <tj@...nel.org>, Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Eric Auger <eric.auger@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        "Raj, Ashok" <ashok.raj@...el.com>, "Wu, Hao" <hao.wu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>
Subject: Re: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and
 allocation APIs

On Thu, Apr 01, 2021 at 01:38:46PM +0000, Liu, Yi L wrote:
> > From: Jean-Philippe Brucker <jean-philippe@...aro.org>
> > Sent: Thursday, April 1, 2021 8:05 PM
> [...]
> > 
> > Also wondering about:
> > 
> > * Querying IOMMU nesting capabilities before binding page tables (which
> >   page table formats are supported?). We were planning to have a VFIO cap,
> >   but I'm guessing we need to go back to the sysfs solution?
> 
> I think it can also be with /dev/ioasid.

Sure, anything to do with page table formats and setting page tables
should go through ioasid.

> > * Invalidation, probably an ioasid_fd ioctl?
> 
> yeah, if we are doing bind/unbind_pagtable via ioasid_fd, then yes,
> invalidation should go this way as well. This is why I worried it may
> fail to meet the requirement from you and Eric.

Yes, all manipulation of page tables, including removing memory ranges, or
setting memory ranges to trigger a page fault behavior should go
through here.

> > * Page faults, page response. From and to devices, and don't necessarily
> >   have a PASID. But needed by vdpa as well, so that's also going through
> >   /dev/ioasid?
> 
> page faults should still be per-device, but the fault event fd may be stored
> in /dev/ioasid. page response would be in /dev/ioasid just like invalidation.

Here you mean non-SVA page faults that are delegated to userspace to handle?

Why would that be per-device?

Can you show the flow you imagine?

Jason