Re: [Qemu-devel] [PATCH] msix: don't mask already masked vectors on reset

[Ladi Prosek]

On Wed, Nov 22, 2017 at 11:46 AM, Marcel Apfelbaum <address@hidden> wrote:
> Hi Ladi,
>
> On 20/11/2017 16:22, Ladi Prosek wrote:
>>
>> msix_mask_all() is supposed to invoke the release vector notifier if the
>> state of the
>> respective vector changed from unmasked or masked.
>
>
> You mean from unmasked "to" masked right?

Yes, that's a typo.

> The way it's currently called from
>>
>> msix_reset(), though, may result in calling the release notifier even if
>> the vector
>> is already masked.
>>
>> 1) msix_reset() clears out the msix_cap field and the msix_table.
>> 2) msix_mask_all() runs with was_masked=false for all vectors because of
>> 1), which
>>     results in calling the release notifier on all vectors.
>> 3) if msix_reset() is subsequently called again, it goes through the same
>> steps and
>>     calls the release notifier on all vectors again.
>>
>
> As far as I can see in the code you are right.(very reset will trigger the
> release notifiers
> again)
>
>> This commit moves msix_mask_all() up so it runs before the device state is
>> lost.
>
>
> OK
>
>> And
>> it adds a call to msix_update_function_masked() so that the device
>> remembers that
>> MSI-X is masked.
>>
>
> msix_update_function_masked checks the msix is enabled or masked-off.
> You are building on the fact the msix will not be enabled to set
> "msix_function_masked" to "true", right?
> (I just want to be sure I understand the patch)

Correct. msix_enabled() will return false because we've just reset

  dev->config[dev->msix_cap + MSIX_CONTROL_OFFSET]

I guess we could also simply assign true to it:

  dev->msix_function_masked = true;

just like msix_init() does.

>> This is likely a low impact issue, found while debugging an already broken
>> device. It
>> is however easy to fix and the expectation that the use and release
>> notifier invocations
>> are always balanced is very natural.
>>
>
> I would leave it (maybe) out of 2.11 because it may expose other bugs
> and we are after rc2 already.
>
> Adding Alex Williamson to see it does not affect device assignment,
> other than that the patch looks OK to me.
>
>
> Thanks,
> Marcel
>
>
>> Signed-off-by: Ladi Prosek <address@hidden>
>> ---
>>   hw/pci/msix.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/hw/pci/msix.c b/hw/pci/msix.c
>> index c944c02135..34656de9b0 100644
>> --- a/hw/pci/msix.c
>> +++ b/hw/pci/msix.c
>> @@ -500,11 +500,12 @@ void msix_reset(PCIDevice *dev)
>>           return;
>>       }
>>       msix_clear_all_vectors(dev);
>> +    msix_mask_all(dev, dev->msix_entries_nr);
>>       dev->config[dev->msix_cap + MSIX_CONTROL_OFFSET] &=
>>             ~dev->wmask[dev->msix_cap + MSIX_CONTROL_OFFSET];
>>       memset(dev->msix_table, 0, dev->msix_entries_nr *
>> PCI_MSIX_ENTRY_SIZE);
>>       memset(dev->msix_pba, 0, QEMU_ALIGN_UP(dev->msix_entries_nr, 64) /
>> 8);
>> -    msix_mask_all(dev, dev->msix_entries_nr);
>> +    msix_update_function_masked(dev);
>>   }
>>     /* PCI spec suggests that devices make it possible for software to
>> configure
>>
>