Re: [Qemu-devel] [PATCH] msi/msix: added API to set MSI message address and data

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Jul 18, 2012 at 11:17:12PM +1000, Alexey Kardashevskiy wrote:
> On 18/07/12 22:43, Michael S. Tsirkin wrote:
> > On Thu, Jun 21, 2012 at 09:39:10PM +1000, Alexey Kardashevskiy wrote:
> >> Added (msi|msix)_set_message() functions.
> >>
> >> Currently msi_notify()/msix_notify() write to these vectors to
> >> signal the guest about an interrupt so the correct values have to
> >> written there by the guest or QEMU.
> >>
> >> For example, POWER guest never initializes MSI/MSIX vectors, instead
> >> it uses RTAS hypercalls. So in order to support MSIX for virtio-pci on
> >> POWER we have to initialize MSI/MSIX message from QEMU.
> >>
> >> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> > 
> > So guests do enable MSI through config space, but do
> > not fill in vectors? 
> 
> Yes. msix_capability_init() calls arch_setup_msi_irqs() which does everything it needs to do (i.e. calls hypervisor) before msix_capability_init() writes PCI_MSIX_FLAGS_ENABLE to the PCI_MSIX_FLAGS register.
> 
> These vectors are the PCI bus addresses, the way they are set is specific for a PCI host controller, I do not see why the current scheme is a bug.

I won't work with any real PCI device, will it? Real pci devices expect
vectors to be written into their memory.

> > Very strange. Are you sure it's not
> > just a guest bug? How does it work for other PCI devices?
> 
> Did not get the question. It works the same for every PCI device under POWER guest.

I mean for real PCI devices.

> > Can't we just fix guest drivers to program the vectors properly?
> > 
> > Also pls address the comment below.
> 
> Comment below.
> 
> > Thanks!
> > 
> >> ---
> >>  hw/msi.c  |   13 +++++++++++++
> >>  hw/msi.h  |    1 +
> >>  hw/msix.c |    9 +++++++++
> >>  hw/msix.h |    2 ++
> >>  4 files changed, 25 insertions(+)
> >>
> >> diff --git a/hw/msi.c b/hw/msi.c
> >> index 5233204..cc6102f 100644
> >> --- a/hw/msi.c
> >> +++ b/hw/msi.c
> >> @@ -105,6 +105,19 @@ static inline uint8_t msi_pending_off(const PCIDevice* dev, bool msi64bit)
> >>      return dev->msi_cap + (msi64bit ? PCI_MSI_PENDING_64 : PCI_MSI_PENDING_32);
> >>  }
> >>  
> >> +void msi_set_message(PCIDevice *dev, MSIMessage msg)
> >> +{
> >> +    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), msg.address);
> >> +    } else {
> >> +        pci_set_long(dev->config + msi_address_lo_off(dev), msg.address);
> >> +    }
> >> +    pci_set_word(dev->config + msi_data_off(dev, msi64bit), msg.data);
> >> +}
> >> +
> > 
> > Please add documentation. Something like
> > 
> > /*
> >  * Special API for POWER to configure the vectors through
> >  * a side channel. Should never be used by devices.
> >  */
> 
> 
> It is useful for any para-virtualized environment I believe, is not it?
> For s390 as well. Of course, if it supports PCI, for example, what I am not sure it does though :)

I expect the normal guest to program the address into MSI register using
config accesses, same way that it enables MSI/MSIX.
Why POWER does it differently I did not yet figure out but I hope
this weirdness is not so widespread.

> >>  bool msi_enabled(const PCIDevice *dev)
> >>  {
> >>      return msi_present(dev) &&
> >> diff --git a/hw/msi.h b/hw/msi.h
> >> index 75747ab..6ec1f99 100644
> >> --- a/hw/msi.h
> >> +++ b/hw/msi.h
> >> @@ -31,6 +31,7 @@ struct MSIMessage {
> >>  
> >>  extern bool msi_supported;
> >>  
> >> +void msi_set_message(PCIDevice *dev, MSIMessage msg);
> >>  bool msi_enabled(const PCIDevice *dev);
> >>  int msi_init(struct PCIDevice *dev, uint8_t offset,
> >>               unsigned int nr_vectors, bool msi64bit, bool msi_per_vector_mask);
> >> diff --git a/hw/msix.c b/hw/msix.c
> >> index ded3c55..5f7d6d3 100644
> >> --- a/hw/msix.c
> >> +++ b/hw/msix.c
> >> @@ -45,6 +45,15 @@ static MSIMessage msix_get_message(PCIDevice *dev, unsigned vector)
> >>      return msg;
> >>  }
> >>  
> >> +void msix_set_message(PCIDevice *dev, int vector, struct MSIMessage msg)
> >> +{
> >> +    uint8_t *table_entry = dev->msix_table_page + vector * PCI_MSIX_ENTRY_SIZE;
> >> +
> >> +    pci_set_quad(table_entry + PCI_MSIX_ENTRY_LOWER_ADDR, msg.address);
> >> +    pci_set_long(table_entry + PCI_MSIX_ENTRY_DATA, msg.data);
> >> +    table_entry[PCI_MSIX_ENTRY_VECTOR_CTRL] &= ~PCI_MSIX_ENTRY_CTRL_MASKBIT;
> >> +}
> >> +
> >>  /* Add MSI-X capability to the config space for the device. */
> >>  /* Given a bar and its size, add MSI-X table on top of it
> >>   * and fill MSI-X capability in the config space.
> >> diff --git a/hw/msix.h b/hw/msix.h
> >> index 50aee82..26a437e 100644
> >> --- a/hw/msix.h
> >> +++ b/hw/msix.h
> >> @@ -4,6 +4,8 @@
> >>  #include "qemu-common.h"
> >>  #include "pci.h"
> >>  
> >> +void msix_set_message(PCIDevice *dev, int vector, MSIMessage msg);
> >> +
> >>  int msix_init(PCIDevice *pdev, unsigned short nentries,
> >>                MemoryRegion *bar,
> >>                unsigned bar_nr, unsigned bar_size);
> >> -- 
> >> 1.7.10
> >>
> >> ps. double '-' and git version is an end-of-patch scissor as I read somewhere, cannot recall where exactly :)
> >>
> >>
> >>
> >>
> >>
> >>
> >> On 21/06/12 20:56, Jan Kiszka wrote:
> >>> On 2012-06-21 12:50, Alexey Kardashevskiy wrote:
> >>>> On 21/06/12 20:38, Jan Kiszka wrote:
> >>>>> On 2012-06-21 12:28, Alexey Kardashevskiy wrote:
> >>>>>> On 21/06/12 17:39, Jan Kiszka wrote:
> >>>>>>> On 2012-06-21 09:18, Alexey Kardashevskiy wrote:
> >>>>>>>>
> >>>>>>>> agrhhh. sha1 of the patch changed after rebasing :)
> >>>>>>>>
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> Added (msi|msix)_(set|get)_message() function for whoever might
> >>>>>>>> want to use them.
> >>>>>>>>
> >>>>>>>> Currently msi_notify()/msix_notify() write to these vectors to
> >>>>>>>> signal the guest about an interrupt so the correct values have to
> >>>>>>>> written there by the guest or QEMU.
> >>>>>>>>
> >>>>>>>> For example, POWER guest never initializes MSI/MSIX vectors, instead
> >>>>>>>> it uses RTAS hypercalls. So in order to support MSIX for virtio-pci on
> >>>>>>>> POWER we have to initialize MSI/MSIX message from QEMU.
> >>>>>>>>
> >>>>>>>> As only set* function are required by now, the "get" functions were added
> >>>>>>>> or made public for a symmetry.
> >>>>>>>>
> >>>>>>>> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> >>>>>>>> ---
> >>>>>>>>  hw/msi.c  |   29 +++++++++++++++++++++++++++++
> >>>>>>>>  hw/msi.h  |    2 ++
> >>>>>>>>  hw/msix.c |   11 ++++++++++-
> >>>>>>>>  hw/msix.h |    3 +++
> >>>>>>>>  4 files changed, 44 insertions(+), 1 deletion(-)
> >>>>>>>>
> >>>>>>>> diff --git a/hw/msi.c b/hw/msi.c
> >>>>>>>> index 5233204..9ad84a4 100644
> >>>>>>>> --- a/hw/msi.c
> >>>>>>>> +++ b/hw/msi.c
> >>>>>>>> @@ -105,6 +105,35 @@ static inline uint8_t msi_pending_off(const PCIDevice* dev, bool msi64bit)
> >>>>>>>>      return dev->msi_cap + (msi64bit ? PCI_MSI_PENDING_64 : PCI_MSI_PENDING_32);
> >>>>>>>>  }
> >>>>>>>>  
> >>>>>>>> +MSIMessage msi_get_message(PCIDevice *dev)
> >>>>>>>
> >>>>>>> MSIMessage msi_get_message(PCIDevice *dev, unsigned vector)
> >>>>>>
> >>>>>>
> >>>>>> Who/how/why is going to calculate the vector here?
> >>>>>>
> >>>>>>>
> >>>>>>>> +{
> >>>>>>>> +    uint16_t flags = pci_get_word(dev->config + msi_flags_off(dev));
> >>>>>>>> +    bool msi64bit = flags & PCI_MSI_FLAGS_64BIT;
> >>>>>>>> +    MSIMessage msg;
> >>>>>>>> +
> >>>>>>>> +    if (msi64bit) {
> >>>>>>>> +        msg.address = pci_get_quad(dev->config + msi_address_lo_off(dev));
> >>>>>>>> +    } else {
> >>>>>>>> +        msg.address = pci_get_long(dev->config + msi_address_lo_off(dev));
> >>>>>>>> +    }
> >>>>>>>> +    msg.data = pci_get_word(dev->config + msi_data_off(dev, msi64bit));
> >>>>>>>
> >>>>>>> And I have this here in addition:
> >>>>>>>
> >>>>>>>     unsigned int nr_vectors = msi_nr_vectors(flags);
> >>>>>>>     ...
> >>>>>>>
> >>>>>>>     if (nr_vectors > 1) {
> >>>>>>>         msg.data &= ~(nr_vectors - 1);
> >>>>>>>         msg.data |= vector;
> >>>>>>>     }
> >>>>>>>
> >>>>>>> See PCI spec and existing code.
> >>>>>>
> >>>>>>
> >>>>>> What for? I really do not get it why someone might want to read something but not real value.
> >>>>>> What PCI code should I look?
> >>>>>
> >>>>> I'm not sure what your use case for reading the message is. For KVM
> >>>>> device assignment it is preparing an alternative message delivery path
> >>>>> for MSI vectors. And for this we will need vector notifier support for
> >>>>> MSI as well. You can check the MSI-X code for corresponding use cases of
> >>>>> msix_get_message.
> >>>>
> >>>>> And when we already have msi_get_message, another logical use case is
> >>>>> msi_notify. See msix.c again.
> >>>>
> >>>> Aaaa.
> >>>>
> >>>> I have no case for reading the message. All I need is writing. And I want it public as I want to use
> >>>> it from hw/spapr_pci.c. You suggested to add reading, I added "get" to be _symmetric_ to "set"
> >>>> ("get" returns what "set" wrote). You want a different thing which I can do but it is not
> >>>> msi_get_message(), it is something like msi_prepare_message(MSImessage msg) or
> >>>> msi_set_vector(uint16_t data) or simply internal kitchen of msi_notify().
> >>>>
> >>>> Still can do what you suggested, it just does not seem right.
> >>>
> >>> It is right - when looking at it from a different angle. ;)
> >>>
> >>> I don't mind if you add msi_get_message now or leave this to me. Likely
> >>> the latter is better as you have no use case for msi_get_message (and
> >>> also msix_get_message!) outside of their modules, thus we should not
> >>> export those functions anyway.
> 
> 
> 
> -- 
> Alexey
>