Re: [PATCH v8 15/17] vfio-user: handle device interrupts

[Stefan Hajnoczi]

On Mon, Apr 25, 2022 at 05:40:01PM +0000, Jag Raman wrote:
> > On Apr 25, 2022, at 6:27 AM, Stefan Hajnoczi <stefanha@redhat.com> wrote:
> > 
> > On Tue, Apr 19, 2022 at 04:44:20PM -0400, Jagannathan Raman wrote:
> >> +static MSIMessage vfu_object_msi_prepare_msg(PCIDevice *pci_dev,
> >> +                                             unsigned int vector)
> >> +{
> >> +    MSIMessage msg;
> >> +
> >> +    msg.address = 0;
> >> +    msg.data = vector;
> >> +
> >> +    return msg;
> >> +}
> >> +
> >> +static void vfu_object_msi_trigger(PCIDevice *pci_dev, MSIMessage msg)
> >> +{
> >> +    vfu_ctx_t *vfu_ctx = pci_dev->irq_opaque;
> >> +
> >> +    vfu_irq_trigger(vfu_ctx, msg.data);
> >> +}
> > 
> > Why did you switch to vfu_object_msi_prepare_msg() +
> > vfu_object_msi_trigger() in this revision?
> 
> We previously did not do this switch because the server didn’t get updates
> to the MSIx table & PBA.
> 
> The latest client version (which is not part of this series) forwards accesses
> to the MSIx table & PBA over to the server. It also reads the PBA set by the
> server. These change make it possible for the server to make this switch.

Interesting. That's different from kernel VFIO. Before vfio-user commits
to a new approach it would be worth checking with Alex that he agrees
with the design.

I remember sending an email asking about why VFIO MSI-X PBA does not
offer the full semantics described in the PCIe spec but didn't get a
response from Alex (Message-Id:
YkMWp0lUJAHhivJA@stefanha-x1.localdomain).

Stefan

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