linux-kernel - Re: [PATCH v3 06/14] vfio/type1: Add VFIO_IOMMU_PASID

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Date:   Thu, 9 Jul 2020 11:05:13 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     "Liu, Yi L" <yi.l.liu@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Tian, Jun J" <jun.j.tian@...el.com>,
        "Sun, Yi Y" <yi.y.sun@...el.com>,
        "jean-philippe@...aro.org" <jean-philippe@...aro.org>,
        "peterx@...hat.com" <peterx@...hat.com>,
        "Wu, Hao" <hao.wu@...el.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v3 06/14] vfio/type1: Add VFIO_IOMMU_PASID_REQUEST
 (alloc/free)

On Thu, 9 Jul 2020 08:27:51 -0600
Alex Williamson <alex.williamson@...hat.com> wrote:

> > So I'm wondering can we fall back to prior proposal which only free
> > one PASID for a free request. how about your opinion?  
> 
> Doesn't it still seem like it would be a useful user interface to have
> a mechanism to free all pasids, by calling with exactly [0, MAX_UINT]?
> I'm not sure if there's another use case for this given than the user
> doesn't have strict control of the pasid values they get.  Thanks,

Yes, I agree free all pasids of a guest is a useful interface. Since all
PASIDs under one VM is already tracked by an IOASID set with its XArray,
I don't see a need to track again in VFIO.

Shall we only free one & free all? IMHO, free range isn't that useful
and not really symmetric to PASID allocation in that allocation is one
at a time.

Can we just add a new flag, e.g.  VFIO_IOMMU_FREE_ALL_PASID, and
ignored th range in free?