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

[Jason Gunthorpe]

On Fri, Dec 10, 2021 at 07:36:12AM +0000, Tian, Kevin wrote:

> /*
>  * The MSIX mappable capability informs that MSIX data of a BAR can be mmapped
>  * which allows direct access to non-MSIX registers which happened to be within
>  * the same system page.
>  *
>  * Even though the userspace gets direct access to the MSIX data, the existing
>  * VFIO_DEVICE_SET_IRQS interface must still be used for MSIX configuration.
     ^^^^^^^^^^^^^^^^^^^^^

It is this I think we don't want, there should be no hypervisor
involvment on installing the addr/data pair

Guessing by what I saw in PPC there is a hypercall to install a MSI
and the guest never touches the page even though it is
mapped. Presumably there is some IR like thing making this secured

PPC has the same basic problem, I think they have a hypercall to
install a MSI, not a hypercall to provision a generic addr/data pair.

Jason