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SubjectRe: [PATCH 2/7] vfio/pci: Lock external INTx masking ops
On Thu, 7 Mar 2024 08:37:53 +0000
"Tian, Kevin" <kevin.tian@intel.com> wrote:

> > From: Alex Williamson <alex.williamson@redhat.com>
> > Sent: Thursday, March 7, 2024 5:15 AM
> >
> > Mask operations through config space changes to DisINTx may race INTx
> > configuration changes via ioctl. Create wrappers that add locking for
> > paths outside of the core interrupt code.
> >
> > In particular, irq_type is updated holding igate, therefore testing
> > is_intx() requires holding igate. For example clearing DisINTx from
> > config space can otherwise race changes of the interrupt configuration.
> >
>
> Looks the suspend path still checks irq_type w/o holding igate:
>
> vdev->pm_intx_masked = ((vdev->irq_type == VFIO_PCI_INTX_IRQ_INDEX) &&
> vfio_pci_intx_mask(vdev));
>
> Is it with assumption that no change of configuration is possible at
> that point?

Yes, I believe this is relatively safe because userspace is frozen at
this point. That's not however to claim that irq_type is absolutely
used consistently after this series. I just didn't see the other
violations rise to the same level as the fixes in this series and
wanted to avoid the distraction. I've stashed a number of patches that
I'd eventually like to post as follow-ups to this series. Thanks,

Alex


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