linux-kernel - Re: [PATCH v6 5/5] vfio/type1: Use mdev bus iommu

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Message-ID: <20201030150625.2dc5fb9b@w520.home>
Date:   Fri, 30 Oct 2020 15:06:25 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Cornelia Huck <cohuck@...hat.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>, "Zeng, Xin" <xin.zeng@...el.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [PATCH v6 5/5] vfio/type1: Use mdev bus iommu_ops for IOMMU
 callbacks

On Fri, 30 Oct 2020 06:16:28 +0000
"Tian, Kevin" <kevin.tian@...el.com> wrote:

> > From: Lu Baolu <baolu.lu@...ux.intel.com>
> > Sent: Friday, October 30, 2020 12:58 PM
> > 
> > With the IOMMU driver registering iommu_ops for the mdev_bus, the
> > IOMMU
> > operations on an mdev could be done in the same way as any normal device
> > (for example, PCI/PCIe). There's no need to distinguish an mdev from
> > others for iommu operations. Remove the unnecessary code.  
> 
> This is really a nice cleanup as the output of this change! :)

It's easy to remove a bunch of code when the result is breaking
everyone else.  Please share with me how SR-IOV backed mdevs continue
to work on AMD platforms, or how they might work on ARM platforms, when
siov_iommu_ops (VT-d only) becomes the one and only provider of
iommu_ops on the mdev bus.  Hard NAK on this series.  Thanks,

Alex