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Date: Fri, 31 Dec 2021 09:58:11 +0800 From: Lu Baolu <baolu.lu@...ux.intel.com> To: Jason Gunthorpe <jgg@...dia.com>, Bjorn Helgaas <helgaas@...nel.org> Cc: baolu.lu@...ux.intel.com, 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 12/31/21 9:10 AM, Lu Baolu wrote: > > On 12/31/21 8:40 AM, Jason Gunthorpe wrote: >> On Thu, Dec 30, 2021 at 04:24:14PM -0600, Bjorn Helgaas wrote: >> >>> I was speculating that maybe the DMA ownership claiming must be done >>> *before* the driver's .probe() method? >> >> This is correct. >> >>> If DMA ownership could be claimed by the .probe() method, we >>> wouldn't need the new flag in struct device_driver. >> >> The other requirement is that every existing driver must claim >> ownership, so pushing this into the device driver's probe op would >> require revising almost every driver in Linux... >> >> In effect the new flag indicates if the driver will do the DMA >> ownership claim in it's probe, or should use the default claim the >> core code does. >> >> In almost every case a driver should do a claim. A driver like >> pci-stub, or a bridge, that doesn't actually operate MMIO on the >> device would be the exception. > > 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. Oh, wait. I didn't think about the hot-plug case. If we call iommu_device_use_dma_api() in bus dma_configure() anyway, we can't bind any (no matter vfio or none-vfio) driver to a device if it's group has already been assigned to user space. It seems that we can't omit this flag. Best regards, baolu
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