Re: [Qemu-devel] [PATCH 1/3] msi/msix: added functions to API to set up message address and data

[Alex Williamson <alex.williamson@redhat.com>]

On Thu, 2012-06-14 at 15:17 +1000, Alexey Kardashevskiy wrote:
> On 14/06/12 14:56, Alex Williamson wrote:
> > On Thu, 2012-06-14 at 14:31 +1000, Alexey Kardashevskiy wrote:
> >> Normally QEMU expects the guest to initialize MSI/MSIX vectors.
> >> However on POWER the guest uses RTAS subsystem to configure MSI/MSIX and
> >> does not write these vectors to device's config space or MSIX BAR.
> >>
> >> On the other hand, msi_notify()/msix_notify() write to these vectors to
> >> signal the guest about an interrupt so we have to write correct vectors
> >> to the devices in order not to change every user of MSI/MSIX.
> >>
> >> The first aim is to support MSIX for virtio-pci on POWER. There is
> >> another patch for POWER coming which introduces a special memory region
> >> where MSI/MSIX vectors point to.
> >>
> >> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> >> ---
> >>  hw/msi.c  |   14 ++++++++++++++
> >>  hw/msi.h  |    1 +
> >>  hw/msix.c |   10 ++++++++++
> >>  hw/msix.h |    3 +++
> >>  4 files changed, 28 insertions(+), 0 deletions(-)
> >>
> >> diff --git a/hw/msi.c b/hw/msi.c
> >> index 5d6ceb6..124878a 100644
> >> --- a/hw/msi.c
> >> +++ b/hw/msi.c
> >> @@ -358,3 +358,17 @@ unsigned int msi_nr_vectors_allocated(const PCIDevice *dev)
> >>      uint16_t flags = pci_get_word(dev->config + msi_flags_off(dev));
> >>      return msi_nr_vectors(flags);
> >>  }
> >> +
> >> +void msi_set_address_data(PCIDevice *dev, uint64_t address, uint16_t data)
> >> +{
> >> +    uint16_t flags = pci_get_word(dev->config + msi_flags_off(dev));
> >> +    bool msi64bit = flags & PCI_MSI_FLAGS_64BIT;
> >> +
> >> +    if (msi64bit) {
> >> +        pci_set_quad(dev->config + msi_address_lo_off(dev), address);
> >> +    } else {
> >> +        pci_set_long(dev->config + msi_address_lo_off(dev), address);
> >> +    }
> >> +    pci_set_word(dev->config + msi_data_off(dev, msi64bit), data);
> >> +}
> > 
> > Why not make it msi_set_message() and pass MSIMessage?  I'd be great if
> > you tossed in a msi_get_message() as well, I think we need it to be able
> > to do a kvm_irqchip_add_msi_route() with MSI.  Thanks,
> 
> 
> I am missing the point. What is that MSIMessage?
> It is just an address and data, making a struct from this is a bit too much :)
> I am totally unfamiliar with kvm_irqchip_add_msi_route to see the bigger picture, sorry.

MSIVectorUseNotifier passes a MSIMessage back to the device when a
vector is unmasked.  We can then add a route in KVM for that message
with kvm_irqchip_add_msi_route.  Finally, kvm_irqchip_add_irqfd allows
us to connect that MSI route to an eventfd, such as from virtio or vfio.
Then MSI eventfds can bypass qemu and be injected directly into KVM and
on into the guest.  So we seem to already have some standardization on
passing address/data via an MSIMessage.

You need a "set" interface, I need a "get" interface.  msix already has
a static msix_get_message().  So I'd suggest that an exported
get/set_message for each seems like the right way to go.  Thanks,

Alex