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

[Michael S. Tsirkin]

On Thu, Jul 19, 2012 at 10:32:40AM +1000, Alexey Kardashevskiy wrote:
> On 19/07/12 01:23, Michael S. Tsirkin wrote:
> > 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 <address@hidden>
> >>>
> >>> 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.
> 
> 
> Yes. And the hypervisor does this. On POWER (at least book3s - server 
> powerpc, the whole config space kitchen is hidden behind RTAS (kind of bios). 
> For the guest, this RTAS is implemented in hypervisor, for the host - in the 
> system firmware. So powerpc linux does not have to have PHB drivers. Kinda 
> cool.
> 
> Usual powerpc server is running without the host linux at all, it is running 
> a hypervisor called pHyp. And every guest knows that it is a guest, there is 
> no full machine emulation, it is para-virtualization. In power-kvm, we 
> replace that pHyp with the host linux and now QEMU plays a hypervisor role. 
> Some day We will move the hypervisor to the host kernel completely (?) but 
> now it is in QEMU.

OKay. So it is a POWER-specific weirdness as I suspected.
Sure, if this is what real hardware does we pretty much have to
emulate this.

> >>> 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.
> 
> 
> In para-virt I would expect the guest not to touch config space at all. At 
> least it should use one interface rather than two but this is how it is.

It's not new that firmware developers consistently make inconsistent
design decisions :)

> >>>>  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 <address@hidden>
> >>>>>>>>>> ---
> >>>>>>>>>>  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
>