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Date:   Thu, 6 May 2021 09:23:48 +0200
From:   Jean-Philippe Brucker <jean-philippe@linaro.org>
To:     Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc:     Jason Gunthorpe <jgg@nvidia.com>,
        "Tian, Kevin" <kevin.tian@intel.com>,
        Alex Williamson <alex.williamson@redhat.com>,
        "Liu, Yi L" <yi.l.liu@intel.com>,
        Auger Eric <eric.auger@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Joerg Roedel <joro@8bytes.org>,
        Lu Baolu <baolu.lu@linux.intel.com>,
        David Woodhouse <dwmw2@infradead.org>,
        "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>,
        "cgroups@vger.kernel.org" <cgroups@vger.kernel.org>,
        Tejun Heo <tj@kernel.org>, Li Zefan <lizefan@huawei.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Jean-Philippe Brucker <jean-philippe@linaro.com>,
        Jonathan Corbet <corbet@lwn.net>,
        "Raj, Ashok" <ashok.raj@intel.com>, "Wu, Hao" <hao.wu@intel.com>,
        "Jiang, Dave" <dave.jiang@intel.com>
Subject: Re: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and
 allocation APIs
Message-ID: <YJOZhPGheTSlHtQc@myrica>
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 <20210504180050.GB1370958@nvidia.com>
 <20210504151154.02908c63@jacob-builder>
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On Wed, May 05, 2021 at 01:04:46PM -0700, Jacob Pan wrote:
> > > For ARM, since the guest owns the per device PASID table. There is no
> > > need to allocate PASIDs from the host nor the hypervisor. Without SWQ,
> > > there is no need for global PASID/SSID either. So PASID being global
> > > for ARM is for simplicity in case of host PASID/SSID.  
> > 
> > It isn't clear how ARM can support PASID and mdev but that is an
> > unrelated issue..
> > 
> AFAIK, the current SMMU device assignment is per RID, since only one stage2
> page tables per RID, not per PASID. This is equivalent to the older VT-d
> spec. prior to scalable mode.

Yes that's right. Since SMMUv3 has a single level-2 page table per RID, it
doesn't support assigning level-1 page tables to guests for mdevs (sub-VF
devices). So no PASIDs for mdevs, which also means each guest has its own
PASID space and the host doesn't track guest PASIDs.

Thanks,
Jean