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Re: [Qemu-devel] [PATCH] pci: Don't deliver MSI/MSI-X messages if bus ma


From: Michael S. Tsirkin
Subject: Re: [Qemu-devel] [PATCH] pci: Don't deliver MSI/MSI-X messages if bus master support is off
Date: Mon, 21 Jul 2014 00:03:01 +0300

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?
Doesn't regulat driver disable MSI?


> 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
> >>
> > 
> > 
> 
> 





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