Re: [Qemu-devel] [PATCH qemu v7 13/14] spapr_pci/spapr_pci_vfio: Support Dynamic DMA Windows (DDW)

[Markus Armbruster]

David Gibson <address@hidden> writes:

> On Thu, Jun 18, 2015 at 09:35:44PM +1000, Alexey Kardashevskiy wrote:
>> On 05/05/2015 10:49 PM, David Gibson wrote:
>> >On Sat, Apr 25, 2015 at 10:24:43PM +1000, Alexey Kardashevskiy wrote:
>> >>This adds support for Dynamic DMA Windows (DDW) option defined by
>> >>the SPAPR specification which allows to have additional DMA window(s)
>> >>
>> >>This implements DDW for emulated and VFIO devices. As all TCE root regions
>> >>are mapped at 0 and 64bit long (and actual tables are child regions),
>> >>this replaces memory_region_add_subregion() with _overlap() to make
>> >>QEMU memory API happy.
>> >>
>> >>This reserves RTAS token numbers for DDW calls.
>> >>
>> >>This implements helpers to interact with VFIO kernel interface.
>> >>
>> >>This changes the TCE table migration descriptor to support dynamic
>> >>tables as from now on, PHB will create as many stub TCE table objects
>> >>as PHB can possibly support but not all of them might be initialized at
>> >>the time of migration because DDW might or might not be requested by
>> >>the guest.
>> >>
>> >>The "ddw" property is enabled by default on a PHB but for compatibility
>> >>the pseries-2.3 machine and older disable it.
>> >>
>> >>This implements DDW for VFIO. The host kernel support is required.
>> >>This adds a "levels" property to PHB to control the number of levels
>> >>in the actual TCE table allocated by the host kernel, 0 is the default
>> >>value to tell QEMU to calculate the correct value. Current hardware
>> >>supports up to 5 levels.
>> >>
>> >>The existing linux guests try creating one additional huge DMA window
>> >>with 64K or 16MB pages and map the entire guest RAM to. If succeeded,
>> >>the guest switches to dma_direct_ops and never calls TCE hypercalls
>> >>(H_PUT_TCE,...) again. This enables VFIO devices to use the entire RAM
>> >>and not waste time on map/unmap later.
>> >>
>> >>This adds 4 RTAS handlers:
>> >>* ibm,query-pe-dma-window
>> >>* ibm,create-pe-dma-window
>> >>* ibm,remove-pe-dma-window
>> >>* ibm,reset-pe-dma-window
>> >>These are registered from type_init() callback.
>> >>
>> >>These RTAS handlers are implemented in a separate file to avoid polluting
>> >>spapr_iommu.c with PCI.
>> >>
>> >>Signed-off-by: Alexey Kardashevskiy <address@hidden>
>> >
>> >Reviewed-by: David Gibson <address@hidden>
>> 
>> I saw this and decided there are no more coments but I was wrong :)
>
> Right.  Note that if I add a Reviewed-by but also make comments, then
> those comments are seeking clarification and maybe suggesting later
> cleanups, but I think the problems are small enough that the patch is
> still ready to go as it is.

You can help the recipient of your comments by putting your R-by behind
the last comment.

Wouldn't be necessary if people never left reams of quoted material
at the end of their replies, but that's a pipe dream :)

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