Re: Advice for implementing MSI-X support on NetBSD Xen 4.11?

[Jan Beulich <jbeulich@xxxxxxxx>]

On 20.07.2020 09:00, Roger Pau Monné wrote:
> On Sun, Jul 19, 2020 at 05:54:28PM +0200, Jaromír Doleček wrote:
>> I've implemented support for using MSI under NetBSD Dom0 with 4.11.
>> This works well.
>>
>> I have some trouble now with getting MSI-X work under Xen.
>> PHYSDEVOP_map_pirq hypercall succeeds just as well as for MSI, but
>> interrupts don't seem to get delivered.
> 
> How are you filling physdev_map_pirq for MSI-X?
> 
> You need to set entry_nr and table_base.
> 
>> MSI-X interrupts work with NetBSD for the same devices when booted
>> natively, without Xen.
>>
>> Can you give me some advice on where to start looking to get this
>> working? Is there perhaps something special to be done within the PCI
>> subsystem to allow Xen to take over?
> 
> Are you enabling the capability and unmasking the interrupt in the
> MSI-X table?
> 
> IIRC the OS also needs to unmask the entry in the MSI-X table in MMIO
> space, as done natively.

Is this effort for PV or PVH? If the former, I don't think Dom0 is
supposed to write directly to any of these structures. This is all
intended to be hypercall based, despite us intercepting and trying
to emulate direct accesses.

Jaromír - are you making use of PHYSDEVOP_prepare_msix?

Jan