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

[Marcel Apfelbaum]

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