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

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Date:   Thu, 1 Apr 2021 13:10:48 +0000
From:   "Liu, Yi L" <yi.l.liu@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>
CC:     "Tian, Kevin" <kevin.tian@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        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: Jason Gunthorpe <jgg@...dia.com>
> Sent: Thursday, April 1, 2021 7:47 PM
[...]
> I'm worried Intel views the only use of PASID in a guest is with
> ENQCMD, but that is not consistent with the industry. We need to see
> normal nested PASID support with assigned PCI VFs.

I'm not quire flow here. Intel also allows PASID usage in guest without
ENQCMD. e.g. Passthru a PF to guest, and use PASID on it without ENQCMD.

[...]

> I'm sure there will be some small differences, and you should clearly
> explain the entire uAPI surface so that soneone from AMD and ARM can
> review it.

good suggestion, will do.

> > - this per-ioasid SVA operations is not aligned with the native SVA usage
> >   model. Native SVA bind is per-device.
> 
> Seems like that is an error in native SVA.
> 
> SVA is a particular mode of the PASID's memory mapping table, it has
> nothing to do with a device.

I think it still has relationship with device. This is determined by the
DMA remapping hierarchy in hardware. e.g. Intel VT-d, the DMA isolation is
enforced first in device granularity and then PASID granularity. SVA makes
usage of both PASID and device granularity isolation.

Regards,
Yi Liu

> Jason