Re: [Qemu-devel] [PATCH v2] msix: don't mask already masked vectors on reset

[Marcel Apfelbaum <marcel@redhat.com>]

On 21/12/2017 16:01, Michael S. Tsirkin wrote:
> On Fri, Dec 08, 2017 at 09:09:06AM -0500, Marcel Apfelbaum wrote:
>>
>>
>> ----- Original Message -----
>>> From: "Ladi Prosek" <lprosek@redhat.com>
>>> To: qemu-devel@nongnu.org
>>> Cc: marcel@redhat.com, geoff@hostfission.com, mst@redhat.com, "alex williamson" <alex.williamson@redhat.com>
>>> Sent: Friday, December 8, 2017 8:31:13 AM
>>> Subject: [PATCH v2] msix: don't mask already masked vectors on reset
>>>
>>> msix_mask_all() is supposed to invoke the release vector notifier if the
>>> state of the
>>> respective vector changed from unmasked to masked. 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.
>>>
>>> This commit moves msix_mask_all() up so it runs before the device state is
>>> lost. And
>>> it adds an assignment to msix_function_masked so that the device remembers
>>> that
>>> MSI-X is masked.
>>>
>>> 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.
>>>
>>> Signed-off-by: Ladi Prosek <lprosek@redhat.com>
>>> ---
>>>
>>> v1->v2:
>>> * fixed typo in commit message "or" -> "to" (Marcel)
>>> * directly set msix_function_masked to true instead of calling
>>>    msix_update_function_masked() (Marcel)
>>>
>>>
>>>   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..d6a4dbdb6b 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);
>>> +    dev->msix_function_masked = true;
>>>   }
>>>   
>>>   /* PCI spec suggests that devices make it possible for software to configure
>>> --
>>> 2.13.6
>>>
>>>
>>
>> Thanks Ladi!
>>
>> Reviewed-by: Marcel Apfelbaum <marcel@redhat.com>
> 
> This breaks make check though.
> 
> Marcel - could you take a look please?
> 

Sure

Thanks,
Marcel