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

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Message-ID: <20210715135757.GC590891@otc-nc-03>
Date:   Thu, 15 Jul 2021 06:57:57 -0700
From:   "Raj, Ashok" <ashok.raj@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     "Tian, Kevin" <kevin.tian@...el.com>,
        Shenming Lu <lushenming@...wei.com>,
        "Alex Williamson (alex.williamson@...hat.com)" 
        <alex.williamson@...hat.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        David Gibson <david@...son.dropbear.id.au>,
        Jason Wang <jasowang@...hat.com>,
        "parav@...lanox.com" <parav@...lanox.com>,
        "Enrico Weigelt, metux IT consult" <lkml@...ux.net>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        Eric Auger <eric.auger@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        "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>,
        "wanghaibin.wang@...wei.com" <wanghaibin.wang@...wei.com>
Subject: Re: [RFC v2] /dev/iommu uAPI proposal

On Thu, Jul 15, 2021 at 09:48:13AM -0300, Jason Gunthorpe wrote:
> On Thu, Jul 15, 2021 at 06:49:54AM +0000, Tian, Kevin wrote:
> 
> > No. You are right on this case. I don't think there is a way to 
> > differentiate one mdev from the other if they come from the
> > same parent and attached by the same guest process. In this
> > case the fault could be reported on either mdev (e.g. the first
> > matching one) to get it fixed in the guest.
> 
> If the IOMMU can't distinguish the two mdevs they are not isolated
> and would have to share a group. Since group sharing is not supported
> today this seems like a non-issue

Does this mean we have to prevent 2 mdev's from same pdev being assigned to
the same guest?