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    SubjectRe: [PATCH v7 06/11] PCI: portdrv: Set driver_managed_dma
    On Mon, Feb 28, 2022 at 08:50:51AM +0800, Lu Baolu wrote:
    > If a switch lacks ACS P2P Request Redirect, a device below the switch can
    > bypass the IOMMU and DMA directly to other devices below the switch, so
    > all the downstream devices must be in the same IOMMU group as the switch
    > itself.
    >
    > The existing VFIO framework allows the portdrv driver to be bound to the
    > bridge while its downstream devices are assigned to user space. The
    > pci_dma_configure() marks the IOMMU group as containing only devices
    > with kernel drivers that manage DMA. Avoid this default behavior for the
    > portdrv driver in order for compatibility with the current VFIO usage.

    It would be nice to explicitly say here how we can look at portdrv
    (and pci_stub) and conclude that ".driver_managed_dma = true" is safe.

    Otherwise I won't know what kind of future change to portdrv might
    make it unsafe.

    > Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
    > Suggested-by: Kevin Tian <kevin.tian@intel.com>
    > Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
    > Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

    Acked-by: Bjorn Helgaas <bhelgaas@google.com>

    > ---
    > drivers/pci/pcie/portdrv_pci.c | 2 ++
    > 1 file changed, 2 insertions(+)
    >
    > diff --git a/drivers/pci/pcie/portdrv_pci.c b/drivers/pci/pcie/portdrv_pci.c
    > index 35eca6277a96..6b2adb678c21 100644
    > --- a/drivers/pci/pcie/portdrv_pci.c
    > +++ b/drivers/pci/pcie/portdrv_pci.c
    > @@ -202,6 +202,8 @@ static struct pci_driver pcie_portdriver = {
    >
    > .err_handler = &pcie_portdrv_err_handler,
    >
    > + .driver_managed_dma = true,
    > +
    > .driver.pm = PCIE_PORTDRV_PM_OPS,
    > };
    >
    > --
    > 2.25.1
    >
    > _______________________________________________
    > iommu mailing list
    > iommu@lists.linux-foundation.org
    > https://lists.linuxfoundation.org/mailman/listinfo/iommu

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