Re: [Qemu-devel] [PATCH] pci: Don't deliver MSI/MSI-X messages if bus master support is off

[Michael S. Tsirkin]

On Mon, Jul 21, 2014 at 12:04:22AM +0200, Jan Kiszka wrote:
> On 2014-07-20 23:03, Michael S. Tsirkin wrote:
> > On Sun, Jul 20, 2014 at 11:45:10PM +0200, Jan Kiszka wrote:
> >> On 2014-07-20 21:48, Michael S. Tsirkin wrote:
> >>> On Sat, Jul 19, 2014 at 06:55:48PM +0200, Jan Kiszka wrote:
> >>>> From: Jan Kiszka <address@hidden>
> >>>>
> >>>> The spec says (and real HW confirms this) that, if the bus master bit
> >>>> is 0, the device will not generate any PCI accesses. MSI and MSI-X
> >>>> messages fall among these.
> >>>>
> >>>> Signed-off-by: Jan Kiszka <address@hidden>
> >>>
> >>> I guess an alternative is for callers to check before
> >>> invoking msi_notify. Please note is this is only option
> >>> when using e.g. irqfd, so this has some advantages.
> >>> Is there a specific device that is affected by this?
> >>> I would expect drivers to disable msi before clearing
> >>> bus master bit ...
> >>
> >> This is about emulating conforming behaviour without touching each and
> >> every device. I stumbled over this while playing with emulated vs. real
> >> Intel HDA.
> > 
> > Right so that's my question.
> > How did you hit it? With a custom driver?
> 
> So to say: with a hand full lines of code to tickle some MSI event out
> of that device for testing purposes.
> 
> > Doesn't regulat driver disable MSI?
> 
> Sure. This is not fixing a regular's driver problem. It's a behavioral
> correction for faulty corner cases.
> 
> Jan

OK based on this I think this is not 2.1 material. Agree?

> > 
> > 
> >> It may not be complete, but I think it's a step forward. Irqfd users
> >> apparently have to do this themselves then, I didn't look into this. But
> >> all the rest should not open-code this logic.
> >>
> >> Jan
> >>
> >>>
> >>>> ---
> >>>>  hw/pci/msi.c  | 4 ++++
> >>>>  hw/pci/msix.c | 4 ++++
> >>>>  2 files changed, 8 insertions(+)
> >>>>
> >>>> diff --git a/hw/pci/msi.c b/hw/pci/msi.c
> >>>> index a4a3040..36b651b 100644
> >>>> --- a/hw/pci/msi.c
> >>>> +++ b/hw/pci/msi.c
> >>>> @@ -285,6 +285,10 @@ void msi_notify(PCIDevice *dev, unsigned int vector)
> >>>>          return;
> >>>>      }
> >>>>  
> >>>> +    if (!(pci_get_word(dev->config + PCI_COMMAND) & 
> >>>> PCI_COMMAND_MASTER)) {
> >>>> +        return;
> >>>> +    }
> >>>> +
> >>>>      msg = msi_get_message(dev, vector);
> >>>>  
> >>>>      MSI_DEV_PRINTF(dev,
> >>>> diff --git a/hw/pci/msix.c b/hw/pci/msix.c
> >>>> index 5c49bfc..c77ae7d 100644
> >>>> --- a/hw/pci/msix.c
> >>>> +++ b/hw/pci/msix.c
> >>>> @@ -437,6 +437,10 @@ void msix_notify(PCIDevice *dev, unsigned vector)
> >>>>          return;
> >>>>      }
> >>>>  
> >>>> +    if (!(pci_get_word(dev->config + PCI_COMMAND) & 
> >>>> PCI_COMMAND_MASTER)) {
> >>>> +        return;
> >>>> +    }
> >>>> +
> >>>>      msg = msix_get_message(dev, vector);
> >>>>  
> >>>>      stl_le_phys(&address_space_memory, msg.address, msg.data);
> >>>> -- 
> >>>> 1.8.1.1.298.ge7eed54
> >>>>
> >>>
> >>>
> >>
> >>
> > 
> > 
> 
>