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

[Jan Kiszka]

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.

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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