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author | Alexey Kardashevskiy <aik@ozlabs.ru> | 2015-06-05 16:35:26 +1000 |
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committer | Michael Ellerman <mpe@ellerman.id.au> | 2015-06-11 15:16:55 +1000 |
commit | e633bc86a922468a82300eef5b9802e17be5e23d (patch) | |
tree | ccbe3f4a7dc46dc8caed2aff7733548ba9d60c30 /Documentation | |
parent | 2157e7b82f3b81f57bd80cd67cef09ef26e5f74c (diff) | |
download | linux-e633bc86a922468a82300eef5b9802e17be5e23d.tar.gz linux-e633bc86a922468a82300eef5b9802e17be5e23d.tar.bz2 linux-e633bc86a922468a82300eef5b9802e17be5e23d.zip |
vfio: powerpc/spapr: Support Dynamic DMA windows
This adds create/remove window ioctls to create and remove DMA windows.
sPAPR defines a Dynamic DMA windows capability which allows
para-virtualized guests to create additional DMA windows on a PCI bus.
The existing linux kernels use this new window to map the entire guest
memory and switch to the direct DMA operations saving time on map/unmap
requests which would normally happen in a big amounts.
This adds 2 ioctl handlers - VFIO_IOMMU_SPAPR_TCE_CREATE and
VFIO_IOMMU_SPAPR_TCE_REMOVE - to create and remove windows.
Up to 2 windows are supported now by the hardware and by this driver.
This changes VFIO_IOMMU_SPAPR_TCE_GET_INFO handler to return additional
information such as a number of supported windows and maximum number
levels of TCE tables.
DDW is added as a capability, not as a SPAPR TCE IOMMU v2 unique feature
as we still want to support v2 on platforms which cannot do DDW for
the sake of TCE acceleration in KVM (coming soon).
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
[aw: for the vfio related changes]
Acked-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Diffstat (limited to 'Documentation')
-rw-r--r-- | Documentation/vfio.txt | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/Documentation/vfio.txt b/Documentation/vfio.txt index dcc37e109c68..1dd3fddfd3a1 100644 --- a/Documentation/vfio.txt +++ b/Documentation/vfio.txt @@ -464,6 +464,25 @@ address is from pre-registered range. This separation helps in optimizing DMA for guests. +6) sPAPR specification allows guests to have an additional DMA window(s) on +a PCI bus with a variable page size. Two ioctls have been added to support +this: VFIO_IOMMU_SPAPR_TCE_CREATE and VFIO_IOMMU_SPAPR_TCE_REMOVE. +The platform has to support the functionality or error will be returned to +the userspace. The existing hardware supports up to 2 DMA windows, one is +2GB long, uses 4K pages and called "default 32bit window"; the other can +be as big as entire RAM, use different page size, it is optional - guests +create those in run-time if the guest driver supports 64bit DMA. + +VFIO_IOMMU_SPAPR_TCE_CREATE receives a page shift, a DMA window size and +a number of TCE table levels (if a TCE table is going to be big enough and +the kernel may not be able to allocate enough of physically contiguous memory). +It creates a new window in the available slot and returns the bus address where +the new window starts. Due to hardware limitation, the user space cannot choose +the location of DMA windows. + +VFIO_IOMMU_SPAPR_TCE_REMOVE receives the bus start address of the window +and removes it. + ------------------------------------------------------------------------------- [1] VFIO was originally an acronym for "Virtual Function I/O" in its |