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

[Ladi Prosek]

On Thu, Dec 7, 2017 at 7:27 PM, Michael S. Tsirkin <address@hidden> wrote:
> On Wed, Nov 22, 2017 at 03:22:50PM +0200, Marcel Apfelbaum wrote:
>> On 22/11/2017 14:32, Ladi Prosek wrote:
>> > 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.
>>
>> Yes, is preferable - I think.
>> If you intend to send V2, please wait first for Alex's remarks if he has any.
>>
>> Thanks,
>> Marcel
>>
>> >
>> > > > 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
>> > > >
>> > >
>
> Do you intend to post v2 or need Marcel to?

I'll post v2 tomorrow.