linux-kernel - Re: [PATCH 2/7] vfio/pci: Lock external INTx masking ops

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Date: Thu, 7 Mar 2024 13:21:29 -0700
From: Alex Williamson <alex.williamson@...hat.com>
To: "Tian, Kevin" <kevin.tian@...el.com>
Cc: "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "eric.auger@...hat.com"
 <eric.auger@...hat.com>, "clg@...hat.com" <clg@...hat.com>, "Chatre,
 Reinette" <reinette.chatre@...el.com>, "linux-kernel@...r.kernel.org"
 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/7] vfio/pci: Lock external INTx masking ops

On Thu, 7 Mar 2024 08:37:53 +0000
"Tian, Kevin" <kevin.tian@...el.com> wrote:

> > From: Alex Williamson <alex.williamson@...hat.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