linux-kernel - RE: [RFC v2] /dev/iommu uAPI proposal

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Date:   Wed, 4 Aug 2021 22:59:21 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>
CC:     David Gibson <david@...son.dropbear.id.au>,
        "Alex Williamson (alex.williamson@...hat.com)" 
        <alex.williamson@...hat.com>,
        "Jean-Philippe Brucker" <jean-philippe@...aro.org>,
        Jason Wang <jasowang@...hat.com>,
        "parav@...lanox.com" <parav@...lanox.com>,
        "Enrico Weigelt, metux IT consult" <lkml@...ux.net>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Shenming Lu <lushenming@...wei.com>,
        Joerg Roedel <joro@...tes.org>,
        Eric Auger <eric.auger@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>, "Wu, Hao" <hao.wu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Kirti Wankhede <kwankhede@...dia.com>,
        "Robin Murphy" <robin.murphy@....com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "David Woodhouse" <dwmw2@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "Lu Baolu" <baolu.lu@...ux.intel.com>
Subject: RE: [RFC v2] /dev/iommu uAPI proposal

> From: Jason Gunthorpe <jgg@...dia.com>
> Sent: Wednesday, August 4, 2021 10:05 PM
> 
> On Mon, Aug 02, 2021 at 02:49:44AM +0000, Tian, Kevin wrote:
> 
> > Can you elaborate? IMO the user only cares about the label (device cookie
> > plus optional vPASID) which is generated by itself when doing the attaching
> > call, and expects this virtual label being used in various spots (invalidation,
> > page fault, etc.). How the system labels the traffic (the physical RID or RID+
> > PASID) should be completely invisible to userspace.
> 
> I don't think that is true if the vIOMMU driver is also emulating
> PASID. Presumably the same is true for other PASID-like schemes.
> 

I'm getting even more confused with this comment. Isn't it the
consensus from day one that physical PASID should not be exposed
to userspace as doing so breaks live migration? with PASID emulation
vIOMMU only cares about vPASID instead of pPASID, and the uAPI
only requires user to register vPASID instead of reporting pPASID
back to userspace...

Thanks
Kevin