Re: [patch 21/32] NTB/msi: Convert to msi_on_each_desc()

Thomas Gleixner
2021-12-01T18:41:11Z

Dave,

please trim your replies.

On Wed, Dec 01 2021 at 09:28, Dave Jiang wrote:

> On 12/1/2021 3:16 AM, Thomas Gleixner wrote:
>> Jason,
>>
>> CC+ IOMMU folks
>>
>> On Tue, Nov 30 2021 at 20:17, Jason Gunthorpe wrote:
>>> On Tue, Nov 30, 2021 at 10:23:16PM +0100, Thomas Gleixner wrote:
>>
>> Though I fear there is also a use case for MSI-X and IMS tied to the
>> same device. That network card you are talking about might end up using
>> MSI-X for a control block and then IMS for the actual network queues
>> when it is used as physical function device as a whole, but that's
>> conceptually a different case.
>
> Hi Thomas. This is actually the IDXD usage for a mediated device passed
> to a guest kernel when we plumb the pass through of IMS to the guest
> rather than doing previous implementation of having a MSIX vector on
> guest backed by IMS.

Which makes a lot of sense.

> The control block for the mediated device is emulated and therefore an
> emulated MSIX vector will be surfaced as vector 0. However the queues
> will backed by IMS vectors. So we end up needing MSIX and IMS coexist
> running on the guest kernel for the same device.

Why? What's wrong with using straight MSI-X for all of them?

Thanks,

tglx