Re: [PATCH v7 07/11] vfio: Set DMA ownership for VFIO devices

[Alex Williamson]

On Mon, 28 Feb 2022 08:50:52 +0800
Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx> wrote:

> Claim group dma ownership when an IOMMU group is set to a container,
> and release the dma ownership once the iommu group is unset from the
> container.
> 
> This change disallows some unsafe bridge drivers to bind to non-ACS
> bridges while devices under them are assigned to user space. This is an
> intentional enhancement and possibly breaks some existing
> configurations. The recommendation to such an affected user would be
> that the previously allowed host bridge driver was unsafe for this use
> case and to continue to enable assignment of devices within that group,
> the driver should be unbound from the bridge device or replaced with the
> pci-stub driver.
> 
> For any bridge driver, we consider it unsafe if it satisfies any of the
> following conditions:
> 
>   1) The bridge driver uses DMA. Calling pci_set_master() or calling any
>      kernel DMA API (dma_map_*() and etc.) is an indicate that the
>      driver is doing DMA.
> 
>   2) If the bridge driver uses MMIO, it should be tolerant to hostile
>      userspace also touching the same MMIO registers via P2P DMA
>      attacks.
> 
> If the bridge driver turns out to be a safe one, it could be used as
> before by setting the driver's .driver_managed_dma field, just like what
> we have done in the pcieport driver.
> 
> Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> ---
>  drivers/vfio/fsl-mc/vfio_fsl_mc.c     |  1 +
>  drivers/vfio/pci/vfio_pci.c           |  1 +
>  drivers/vfio/platform/vfio_amba.c     |  1 +
>  drivers/vfio/platform/vfio_platform.c |  1 +
>  drivers/vfio/vfio.c                   | 10 +++++++++-
>  5 files changed, 13 insertions(+), 1 deletion(-)

Acked-by: Alex Williamson <alex.williamson@xxxxxxxxxx>