linux-kernel - Re: [PATCH 05/10] iommu/ioasid: Create an IOASID set for host SVA use

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Message-ID: <20200415151043.GB738821@myrica>
Date:   Wed, 15 Apr 2020 17:10:43 +0200
From:   Jean-Philippe Brucker <jean-philippe@...aro.org>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     Joerg Roedel <joro@...tes.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Yi Liu <yi.l.liu@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        Jonathan Cameron <jic23@...nel.org>,
        Eric Auger <eric.auger@...hat.com>
Subject: Re: [PATCH 05/10] iommu/ioasid: Create an IOASID set for host SVA use

On Mon, Apr 13, 2020 at 03:06:31PM -0700, Jacob Pan wrote:
> > > > But quotas are only necessary for VMs, when the host shares the
> > > > PASID space with them (which isn't a use-case for Arm systems as
> > > > far as I know, each VM gets its own PASID space).  
> > > Is there a host-guest PASID translation? or the PASID used by the
> > > VM is physical PASID? When a page request comes in to SMMU, how
> > > does it know the owner of the PASID if PASID range can overlap
> > > between host and guest?  
> > 
> > We assign PCI functions to VMs, so Page Requests are routed with
> > RID:PASID, not PASID alone. The SMMU finds the struct device
> > associated with the RID, and submits the fault with
> > iommu_report_device_fault(). If the VF is assigned to a VM, then the
> > page request gets injected into the VM, otherwise it uses the host
> > IOPF handler
> > 
> Got it, VM private PASID space works then.
> For VM, the IOASID search is within the VM ioasid_set.
> For SVA, the IOASID search is within host default set.
> Should be faster than global search once we have per set xarray.
> I guess the PASID table is per VM instead of per RID (device)? Sorry if
> you already answered it before.

The PASID table is per IOMMU domain, so it's closer to per RID than per
VM, unless userspace puts all devices in the same VFIO container (hence in
the same IOMMU domain).

Thanks,
Jean