Re: [RFC PATCH V1 04/12] xen/arm: Introduce arch specific bits for IOREQ/DM features

[Jan Beulich <jbeulich@xxxxxxxx>]

On 06.08.2020 13:08, Julien Grall wrote:
> On 05/08/2020 20:30, Oleksandr wrote:
>> I was thinking how to split handle_hvm_io_completion() 
>> gracefully but I failed find a good solution for that, so decided to add 
>> two stubs (msix_write_completion and handle_realmode_completion) on Arm. 
>> I could add a comment describing why they are here if appropriate. But 
>> if you think they shouldn't be called from the common code in any way, I 
>> will try to split it.
> 
> I am not entirely sure what msix_write_completion is meant to do on x86. 
> Is it dealing with virtual MSIx? Maybe Jan, Roger or Paul could help?

Due to the split brain model of handling PCI pass-through (between
Xen and qemu), a guest writing to an MSI-X entry needs this write
handed to qemu, and upon completion of the write there Xen also
needs to take some extra action.

Jan