linux-kernel - Re: [RFC 17/20] iommu/iommufd: Report iova range to userspace

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Date:   Wed, 29 Sep 2021 09:31:18 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Jean-Philippe Brucker <jean-philippe@...aro.org>
Cc:     "Liu, Yi L" <yi.l.liu@...el.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "hch@....de" <hch@....de>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "parav@...lanox.com" <parav@...lanox.com>,
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        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "lushenming@...wei.com" <lushenming@...wei.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "corbet@....net" <corbet@....net>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "yi.l.liu@...ux.intel.com" <yi.l.liu@...ux.intel.com>,
        "Tian, Jun J" <jun.j.tian@...el.com>, "Wu, Hao" <hao.wu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "jacob.jun.pan@...ux.intel.com" <jacob.jun.pan@...ux.intel.com>,
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        "robin.murphy@....com" <robin.murphy@....com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
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        "david@...son.dropbear.id.au" <david@...son.dropbear.id.au>,
        "nicolinc@...dia.com" <nicolinc@...dia.com>
Subject: Re: [RFC 17/20] iommu/iommufd: Report iova range to userspace

On Wed, Sep 29, 2021 at 01:07:56PM +0100, Jean-Philippe Brucker wrote:

> Yes, so the guest knows the size of GPA it can write into the page table.
> For Arm SMMU the GPA size is determined by both the SMMU implementation
> and the host kernel configuration. But maybe that could also be
> vendor-specific, if other architectures don't need to communicate it. 

I think there should be a dedicated query to return HW specific
parmaters for a user page table format. Somehow I think there will be
a lot of these.

So 'user page table format arm smmu v1' can be queried to return its
own unique struct that has everything needed to operate that format of
page table.

Userspace already needs to know how to form that specific HW PTEs,
so processing a HW specific query is not a problem.

Jason