linux-kernel - Re: [PATCH v2 1/3] docs: IOMMU user API

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Date:   Tue, 16 Jun 2020 08:22:12 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        "Lu Baolu" <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Yi Liu <yi.l.liu@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        "Christoph Hellwig" <hch@...radead.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Eric Auger <eric.auger@...hat.com>,
        Jonathan Corbet <corbet@....net>, jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v2 1/3] docs: IOMMU user API

On Thu, 11 Jun 2020 17:27:27 -0700
Jacob Pan <jacob.jun.pan@...ux.intel.com> wrote:

> > 
> > But then I thought it even better if VFIO leaves the entire
> > copy_from_user() to the layer consuming it.
> >   
> OK. Sounds good, that was what Kevin suggested also. I just wasn't
> sure how much VFIO wants to inspect, I thought VFIO layer wanted to
> do a sanity check.
> 
> Anyway, I will move copy_from_user to iommu uapi layer.

Just one more point brought up by Yi when we discuss this offline.

If we move copy_from_user to iommu uapi layer, then there will be
multiple copy_from_user calls for the same data when a VFIO container
has multiple domains, devices. For bind, it might be OK. But might be
additional overhead for TLB flush request from the guest.

Thoughts?

Jacob