Re: [Qemu-ppc] [PATCH qemu v10 00/14] spapr: vfio: Enable Dynamic DMA windows (DDW)

[David Gibson]

On Mon, Jul 06, 2015 at 12:10:56PM +1000, Alexey Kardashevskiy wrote:
> 
> (cut-n-paste from kernel patchset)
> 
> Each Partitionable Endpoint (IOMMU group) has an address range on a PCI bus
> where devices are allowed to do DMA. These ranges are called DMA windows.
> By default, there is a single DMA window, 1 or 2GB big, mapped at zero
> on a PCI bus.
> 
> PAPR defines a DDW RTAS API which allows pseries guests
> querying the hypervisor about DDW support and capabilities (page size mask
> for now). A pseries guest may request an additional (to the default)
> DMA windows using this RTAS API.
> The existing pseries Linux guests request an additional window as big as
> the guest RAM and map the entire guest window which effectively creates
> direct mapping of the guest memory to a PCI bus.
> 
> This patchset reworks PPC64 IOMMU code and adds necessary structures
> to support big windows.
> 
> Once a Linux guest discovers the presence of DDW, it does:
> 1. query hypervisor about number of available windows and page size masks;
> 2. create a window with the biggest possible page size (today 4K/64K/16M);
> 3. map the entire guest RAM via H_PUT_TCE* hypercalls;
> 4. switche dma_ops to direct_dma_ops on the selected PE.
> 
> Once this is done, H_PUT_TCE is not called anymore for 64bit devices and
> the guest does not waste time on DMA map/unmap operations.
> 
> Note that 32bit devices won't use DDW and will keep using the default
> DMA window so KVM optimizations will be required (to be posted later).
> 
> This patchset adds DDW support for pseries. The host kernel changes are
> required, available in the current upstream.
> 
> This patchset is based on git://github.com/dgibson/qemu.git spapr-next branch.
> 
> Please comment. Thanks!

I've applied this to my "spapr-dev" branch.  Here's what needs to
happen before I move it into spapr-next (which is what I'll be pushing
to Alex Graf).

 * For you and Gavin to test it to see that DDW and EEH work properly
   together
 * Some word from Alex W on how he wants to go about merging 12-13/14
 * Some indication about who should be merging 2/14
 * Review from at least one more person - I've looked at so many
   versions of the ddw patches I no longer trust that I've got it all
   straight in my head

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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