linux-kernel - RE: [PATCH 1/7] vfio/pci: Disable auto-enable of exclusive INTx IRQ

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Message-ID: <BN9PR11MB5276DBB5FBC36939EB39A3CA8C272@BN9PR11MB5276.namprd11.prod.outlook.com>
Date: Fri, 8 Mar 2024 07:23:21 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Alex Williamson <alex.williamson@...hat.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 1/7] vfio/pci: Disable auto-enable of exclusive INTx IRQ

> From: Alex Williamson <alex.williamson@...hat.com>
> Sent: Friday, March 8, 2024 4:24 AM
> 
> On Thu, 7 Mar 2024 08:39:16 +0000
> "Tian, Kevin" <kevin.tian@...el.com> wrote:
> 
> > > From: Alex Williamson <alex.williamson@...hat.com>
> > > Sent: Thursday, March 7, 2024 5:15 AM
> > >
> > > Currently for devices requiring masking at the irqchip for INTx, ie.
> > > devices without DisINTx support, the IRQ is enabled in request_irq()
> > > and subsequently disabled as necessary to align with the masked status
> > > flag.  This presents a window where the interrupt could fire between
> > > these events, resulting in the IRQ incrementing the disable depth twice.
> > > This would be unrecoverable for a user since the masked flag prevents
> > > nested enables through vfio.
> > >
> > > Instead, invert the logic using IRQF_NO_AUTOEN such that exclusive INTx
> > > is never auto-enabled, then unmask as required.
> > >
> > > Fixes: 89e1f7d4c66d ("vfio: Add PCI device driver")
> > > Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
> >
> > CC stable?
> 
> I've always found that having a Fixes: tag is sufficient to get picked
> up for stable, so I typically don't do both.  If it helps out someone's
> process I'd be happy to though.  Thanks,
> 

According to "Documentation/process/submitting-patches.rst":

  Note: Attaching a Fixes: tag does not subvert the stable kernel rules
  process nor the requirement to Cc: stable@...r.kernel.org on all stable
  patch candidates. For more information, please read
  Documentation/process/stable-kernel-rules.rst.

Probably it's fine as long as the stable kernel maintainers don't complain. 😊