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

[Jan Kiszka <jan.kiszka@web.de>]

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On 2014-07-22 21:06, Michael S. Tsirkin wrote:
> 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 <jan.kiszka@siemens.com>
>>>>>>
>>>>>> 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 <jan.kiszka@siemens.com>
>>>>>
>>>>> 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?

Agree.

I'll look into Paolo's suggestion how to model this asap.

Jan



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