Re: [Qemu-devel] [PATCH] RFC kvm irqfd: add directly mapped MSI IRQ support

[Anthony Liguori <anthony@codemonkey.ws>]

Alex Williamson <alex.williamson@redhat.com> writes:

> On Sun, 2013-06-23 at 10:06 -0500, Anthony Liguori wrote:
>> On Thu, Jun 20, 2013 at 11:46 PM, Alex Williamson
>> <alex.williamson@redhat.com> wrote:
>> > On Fri, 2013-06-21 at 12:49 +1000, Alexey Kardashevskiy wrote:
>> >> On 06/21/2013 12:34 PM, Alex Williamson wrote:
>> >>
>> >>
>> >> Do not follow you, sorry. For x86, is it that MSI routing table which is
>> >> updated via KVM_SET_GSI_ROUTING in KVM? When there is no KVM, what piece of
>> >> code responds on msi_notify() in qemu-x86 and does qemu_irq_pulse()?
>> >
>> > vfio_msi_interrupt->msi[x]_notify->stl_le_phys(msg.address, msg.data)
>> >
>> > This writes directly to the interrupt block on the vCPU.  With KVM, the
>> > in-kernel APIC does the same write, where the pin to MSIMessage is setup
>> > by kvm_irqchip_add_msi_route and the pin is pulled by an irqfd.
>> 
>> What is this "interrupt block on the vCPU" you speak of?  I reviewed
>> the SDM and see nothing in the APIC protocol or the brief description
>> of MSI as a PCI concept that would indicate anything except that the
>> PHB handles MSI writes and feeds them to the I/O APIC.
>
> In all likelihood I'm recalling ia64 details and trying to apply them to
> x86.  Does the MSIMessage not actually get written to the LAPIC on the
> CPU?  Thanks,

There definitely isn't an APIC message for MSI specifically.  I think
the only question is whether the PHB sits on the APIC bus and can
generate an APIC message directly or whether it has a private interface
to the IO APIC to do it.

I suspect that there are systems that do either.  But the important
point is that MSI writes are interpreted by the PHB either way.

Regards,

Anthony Liguori

>
> Alex
>
>> In fact, the wikipedia article on MSI has:
>> 
>> "A common misconception with Message Signaled Interrupts is that they
>> allow the device to send data to a processor as part of the interrupt.
>> The data that is sent as part of the write is used by the chipset to
>> determine which interrupt to trigger on which processor; it is not
>> available for the device to communicate additional information to the
>> interrupt handler."
>> 
>> > Do I understand that on POWER the MSI from the device is intercepted at
>> > the PHB and converted to an IRQ that's triggered by some means other
>> > than a MSI write?
>> 
>> This is exactly the same thing that happens on x86, no?  Can you point
>> me to something in the SDM that says otherwise?
>> 
>> Regards,
>> 
>> Anthony Liguori
>> 
>> >  So to correctly model the hardware, vfio should do a
>> > msi_notify() that does a stl_le_phys that terminates at this IRQ
>> > remapper thing and in turn toggles a qemu_irq.  MSIMessage is only
>> > extraneous data if you want to skip over hardware blocks.
>> >
>> > Maybe you could add a device parameter to kvm_irqchip_add_msi_route so
>> > that it can be implemented on POWER without this pci_bus_map_msi
>> > interface that seems very unique to POWER.  Thanks,
>> >
>> > Alex
>> >
>> >> >>>> ---
>> >> >>>>  hw/misc/vfio.c           |   11 +++++++++--
>> >> >>>>  hw/pci/pci.c             |   13 +++++++++++++
>> >> >>>>  hw/ppc/spapr_pci.c       |   13 +++++++++++++
>> >> >>>>  hw/virtio/virtio-pci.c   |   26 ++++++++++++++++++++------
>> >> >>>>  include/hw/pci/pci.h     |    4 ++++
>> >> >>>>  include/hw/pci/pci_bus.h |    1 +
>> >> >>>>  6 files changed, 60 insertions(+), 8 deletions(-)
>> >> >>>>
>> >> >>>> diff --git a/hw/misc/vfio.c b/hw/misc/vfio.c
>> >> >>>> index 14aac04..2d9eef7 100644
>> >> >>>> --- a/hw/misc/vfio.c
>> >> >>>> +++ b/hw/misc/vfio.c
>> >> >>>> @@ -639,7 +639,11 @@ static int vfio_msix_vector_do_use(PCIDevice *pdev, unsigned int nr,
>> >> >>>>       * Attempt to enable route through KVM irqchip,
>> >> >>>>       * default to userspace handling if unavailable.
>> >> >>>>       */
>> >> >>>> -    vector->virq = msg ? kvm_irqchip_add_msi_route(kvm_state, *msg) : -1;
>> >> >>>> +
>> >> >>>> +    vector->virq = msg ? pci_bus_map_msi(vdev->pdev.bus, *msg) : -1;
>> >> >>>> +    if (vector->virq < 0) {
>> >> >>>> +        vector->virq = msg ? kvm_irqchip_add_msi_route(kvm_state, *msg) : -1;
>> >> >>>> +    }
>> >> >>>>      if (vector->virq < 0 ||
>> >> >>>>          kvm_irqchip_add_irqfd_notifier(kvm_state, &vector->interrupt,
>> >> >>>>                                         vector->virq) < 0) {
>> >> >>>> @@ -807,7 +811,10 @@ retry:
>> >> >>>>           * Attempt to enable route through KVM irqchip,
>> >> >>>>           * default to userspace handling if unavailable.
>> >> >>>>           */
>> >> >>>> -        vector->virq = kvm_irqchip_add_msi_route(kvm_state, msg);
>> >> >>>> +        vector->virq = pci_bus_map_msi(vdev->pdev.bus, msg);
>> >> >>>> +        if (vector->virq < 0) {
>> >> >>>> +            vector->virq = kvm_irqchip_add_msi_route(kvm_state, msg);
>> >> >>>> +        }
>> >> >>>>          if (vector->virq < 0 ||
>> >> >>>>              kvm_irqchip_add_irqfd_notifier(kvm_state, &vector->interrupt,
>> >> >>>>                                             vector->virq) < 0) {
>> >> >>>> diff --git a/hw/pci/pci.c b/hw/pci/pci.c
>> >> >>>> index a976e46..a9875e9 100644
>> >> >>>> --- a/hw/pci/pci.c
>> >> >>>> +++ b/hw/pci/pci.c
>> >> >>>> @@ -1254,6 +1254,19 @@ void pci_device_set_intx_routing_notifier(PCIDevice *dev,
>> >> >>>>      dev->intx_routing_notifier = notifier;
>> >> >>>>  }
>> >> >>>>
>> >> >>>> +void pci_bus_set_map_msi_fn(PCIBus *bus, pci_map_msi_fn map_msi_fn)
>> >> >>>> +{
>> >> >>>> +    bus->map_msi = map_msi_fn;
>> >> >>>> +}
>> >> >>>> +
>> >> >>>> +int pci_bus_map_msi(PCIBus *bus, MSIMessage msg)
>> >> >>>> +{
>> >> >>>> +    if (bus->map_msi) {
>> >> >>>> +        return bus->map_msi(bus, msg);
>> >> >>>> +    }
>> >> >>>> +    return -1;
>> >> >>>> +}
>> >> >>>> +
>> >> >>>>  /*
>> >> >>>>   * PCI-to-PCI bridge specification
>> >> >>>>   * 9.1: Interrupt routing. Table 9-1
>> >> >>>> diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c
>> >> >>>> index 80408c9..9ef9a29 100644
>> >> >>>> --- a/hw/ppc/spapr_pci.c
>> >> >>>> +++ b/hw/ppc/spapr_pci.c
>> >> >>>> @@ -500,6 +500,18 @@ static void spapr_msi_write(void *opaque, hwaddr addr,
>> >> >>>>      qemu_irq_pulse(xics_get_qirq(spapr->icp, irq));
>> >> >>>>  }
>> >> >>>>
>> >> >>>> +static int spapr_msi_get_irq(PCIBus *bus, MSIMessage msg)
>> >> >>>> +{
>> >> >>>> +    DeviceState *par = bus->qbus.parent;
>> >> >>>> +    sPAPRPHBState *sphb = (sPAPRPHBState *) par;
>> >> >>>> +    unsigned long addr = msg.address - sphb->msi_win_addr;
>> >> >>>> +    int ndev = addr >> 16;
>> >> >>>> +    int vec = ((addr & 0xFFFF) >> 2) | msg.data;
>> >> >>>> +    uint32_t irq = sphb->msi_table[ndev].irq + vec;
>> >> >>>> +
>> >> >>>> +    return (int)irq;
>> >> >>>> +}
>> >> >>>> +
>> >> >>>>  static const MemoryRegionOps spapr_msi_ops = {
>> >> >>>>      /* There is no .read as the read result is undefined by PCI spec */
>> >> >>>>      .read = NULL,
>> >> >>>> @@ -664,6 +676,7 @@ static int _spapr_phb_init(SysBusDevice *s)
>> >> >>>>
>> >> >>>>          sphb->lsi_table[i].irq = irq;
>> >> >>>>      }
>> >> >>>> +    pci_bus_set_map_msi_fn(bus, spapr_msi_get_irq);
>> >> >>>>
>> >> >>>>      return 0;
>> >> >>>>  }
>> >> >>>> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
>> >> >>>> index d309416..587f53e 100644
>> >> >>>> --- a/hw/virtio/virtio-pci.c
>> >> >>>> +++ b/hw/virtio/virtio-pci.c
>> >> >>>> @@ -472,6 +472,8 @@ static unsigned virtio_pci_get_features(DeviceState *d)
>> >> >>>>      return proxy->host_features;
>> >> >>>>  }
>> >> >>>>
>> >> >>>> +extern int spapr_msi_get_irq(PCIBus *bus, MSIMessage *msg);
>> >> >>>> +
>> >> >>>>  static int kvm_virtio_pci_vq_vector_use(VirtIOPCIProxy *proxy,
>> >> >>>>                                          unsigned int queue_no,
>> >> >>>>                                          unsigned int vector,
>> >> >>>> @@ -481,7 +483,10 @@ static int kvm_virtio_pci_vq_vector_use(VirtIOPCIProxy *proxy,
>> >> >>>>      int ret;
>> >> >>>>
>> >> >>>>      if (irqfd->users == 0) {
>> >> >>>> -        ret = kvm_irqchip_add_msi_route(kvm_state, msg);
>> >> >>>> +        ret = pci_bus_map_msi(proxy->pci_dev.bus, msg);
>> >> >>>> +        if (ret < 0) {
>> >> >>>> +            ret = kvm_irqchip_add_msi_route(kvm_state, msg);
>> >> >>>> +        }
>> >> >>>>          if (ret < 0) {
>> >> >>>>              return ret;
>> >> >>>>          }
>> >> >>>> @@ -609,14 +614,23 @@ static int virtio_pci_vq_vector_unmask(VirtIOPCIProxy *proxy,
>> >> >>>>      VirtQueue *vq = virtio_get_queue(proxy->vdev, queue_no);
>> >> >>>>      EventNotifier *n = virtio_queue_get_guest_notifier(vq);
>> >> >>>>      VirtIOIRQFD *irqfd;
>> >> >>>> -    int ret = 0;
>> >> >>>> +    int ret = 0, tmp;
>> >> >>>>
>> >> >>>>      if (proxy->vector_irqfd) {
>> >> >>>>          irqfd = &proxy->vector_irqfd[vector];
>> >> >>>> -        if (irqfd->msg.data != msg.data || irqfd->msg.address != msg.address) {
>> >> >>>> -            ret = kvm_irqchip_update_msi_route(kvm_state, irqfd->virq, msg);
>> >> >>>> -            if (ret < 0) {
>> >> >>>> -                return ret;
>> >> >>>> +
>> >> >>>> +        tmp = pci_bus_map_msi(proxy->pci_dev.bus, msg);
>> >> >>>> +        if (tmp >= 0) {
>> >> >>>> +            if (irqfd->virq != tmp) {
>> >> >>>> +                fprintf(stderr, "FIXME: MSI(-X) vector has changed from %X to %x\n",
>> >> >>>> +                        irqfd->virq, tmp);
>> >> >>>> +            }
>> >> >>>> +        } else {
>> >> >>>> +            if (irqfd->msg.data != msg.data || irqfd->msg.address != msg.address) {
>> >> >>>> +                ret = kvm_irqchip_update_msi_route(kvm_state, irqfd->virq, msg);
>> >> >>>> +                if (ret < 0) {
>> >> >>>> +                    return ret;
>> >> >>>> +                }
>> >> >>>>              }
>> >> >>>>          }
>> >> >>>>      }
>> >> >>>> diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
>> >> >>>> index 8797802..632739a 100644
>> >> >>>> --- a/include/hw/pci/pci.h
>> >> >>>> +++ b/include/hw/pci/pci.h
>> >> >>>> @@ -332,6 +332,7 @@ MemoryRegion *pci_address_space_io(PCIDevice *dev);
>> >> >>>>  typedef void (*pci_set_irq_fn)(void *opaque, int irq_num, int level);
>> >> >>>>  typedef int (*pci_map_irq_fn)(PCIDevice *pci_dev, int irq_num);
>> >> >>>>  typedef PCIINTxRoute (*pci_route_irq_fn)(void *opaque, int pin);
>> >> >>>> +typedef int (*pci_map_msi_fn)(PCIBus *bus, MSIMessage msg);
>> >> >>>>
>> >> >>>>  typedef enum {
>> >> >>>>      PCI_HOTPLUG_DISABLED,
>> >> >>>> @@ -375,6 +376,9 @@ bool pci_intx_route_changed(PCIINTxRoute *old, PCIINTxRoute *new);
>> >> >>>>  void pci_bus_fire_intx_routing_notifier(PCIBus *bus);
>> >> >>>>  void pci_device_set_intx_routing_notifier(PCIDevice *dev,
>> >> >>>>                                            PCIINTxRoutingNotifier notifier);
>> >> >>>> +void pci_bus_set_map_msi_fn(PCIBus *bus, pci_map_msi_fn map_msi_fn);
>> >> >>>> +int pci_bus_map_msi(PCIBus *bus, MSIMessage msg);
>> >> >>>> +
>> >> >>>>  void pci_device_reset(PCIDevice *dev);
>> >> >>>>  void pci_bus_reset(PCIBus *bus);
>> >> >>>>
>> >> >>>> diff --git a/include/hw/pci/pci_bus.h b/include/hw/pci/pci_bus.h
>> >> >>>> index 66762f6..81efd2b 100644
>> >> >>>> --- a/include/hw/pci/pci_bus.h
>> >> >>>> +++ b/include/hw/pci/pci_bus.h
>> >> >>>> @@ -16,6 +16,7 @@ struct PCIBus {
>> >> >>>>      pci_set_irq_fn set_irq;
>> >> >>>>      pci_map_irq_fn map_irq;
>> >> >>>>      pci_route_irq_fn route_intx_to_irq;
>> >> >>>> +    pci_map_msi_fn map_msi;
>> >> >>>>      pci_hotplug_fn hotplug;
>> >> >>>>      DeviceState *hotplug_qdev;
>> >> >>>>      void *irq_opaque;
>> >> >>>
>> >> >>>
>> >> >>>
>> >> >>
>> >> >>
>> >> >
>> >> >
>> >> >
>> >>
>> >>
>> >
>> >
>> >
>> >