Messages in this thread | | | Date | Thu, 15 Oct 2015 15:40:25 -0700 | From | Stephen Hemminger <> | Subject | Re: [RFC PATCH v2] vfio: Include No-IOMMU mode |
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On Wed, 14 Oct 2015 15:51:18 -0600 Alex Williamson <alex.williamson@redhat.com> wrote:
> There is really no way to safely give a user full access to a DMA > capable device without an IOMMU to protect the host system. There is > also no way to provide DMA translation, for use cases such as device > assignment to virtual machines. However, there are still those users > that want userspace drivers even under those conditions. The UIO > driver exists for this use case, but does not provide the degree of > device access and programming that VFIO has. In an effort to avoid > code duplication, this introduces a No-IOMMU mode for VFIO. > > This mode requires building VFIO with CONFIG_VFIO_NOIOMMU and enabling > the "enable_unsafe_noiommu_mode" option on the vfio driver. This > should make it very clear that this mode is not safe. Additionally, > CAP_SYS_RAWIO privileges are necessary to work with groups and > containers using this mode. Groups making use of this support are > named /dev/vfio/noiommu-$GROUP and can only make use of the special > VFIO_NOIOMMU_IOMMU for the container. Use of this mode, specifically > binding a device without a native IOMMU group to a VFIO bus driver > will taint the kernel and should therefore not be considered > supported. This patch includes no-iommu support for the vfio-pci bus > driver only. > > Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
The concept looks good.
I am trying it now to see how well this works for the use case of DPDK in a VM.
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