linux-kernel - Re: [PATCH v4 03/13] PCI: pci_stub: Suppress kernel DMA ownership auto-claiming

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Message-ID: <2bbe6e20-6b1a-64ae-a4c6-2f414a8665f2@linux.intel.com>
Date:   Tue, 4 Jan 2022 09:54:31 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     baolu.lu@...ux.intel.com, Bjorn Helgaas <helgaas@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Joerg Roedel <joro@...tes.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Christoph Hellwig <hch@...radead.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Dan Williams <dan.j.williams@...el.com>, rafael@...nel.org,
        Diana Craciun <diana.craciun@....nxp.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        Chaitanya Kulkarni <kch@...dia.com>,
        Stuart Yoder <stuyoder@...il.com>,
        Laurentiu Tudor <laurentiu.tudor@....com>,
        Thierry Reding <thierry.reding@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Li Yang <leoyang.li@....com>,
        Dmitry Osipenko <digetx@...il.com>,
        iommu@...ts.linux-foundation.org, linux-pci@...r.kernel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 03/13] PCI: pci_stub: Suppress kernel DMA ownership
 auto-claiming

On 1/4/22 3:53 AM, Jason Gunthorpe wrote:
> On Fri, Dec 31, 2021 at 09:10:43AM +0800, Lu Baolu wrote:
> 
>> We still need to call iommu_device_use_dma_api() in bus dma_configure()
>> callback. But we can call iommu_device_unuse_dma_api() in the .probe()
>> of vfio (and vfio-approved) drivers, so that we don't need the new flag
>> anymore.
> 
> No, we can't. The action that iommu_device_use_dma_api() takes is to
> not call probe, it obviously cannot be undone by code inside probe.

Yes. Agreed.

> Jason
> 

Best regards,
baolu