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

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Date:   Thu, 1 Apr 2021 13:38:46 +0000
From:   "Liu, Yi L" <yi.l.liu@...el.com>
To:     Jean-Philippe Brucker <jean-philippe@...aro.org>
CC:     Jason Gunthorpe <jgg@...dia.com>,
        "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

> 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.

> 
> * 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.

> * 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.

Regards,
Yi Liu

> 
> Thanks,
> Jean