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

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Message-ID: <20240308170546.GS9225@ziepe.ca>
Date: Fri, 8 Mar 2024 13:05:46 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: Alex Williamson <alex.williamson@...hat.com>
Cc: "Tian, Kevin" <kevin.tian@...el.com>,
	"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

On Thu, Mar 07, 2024 at 01:23:48PM -0700, Alex Williamson wrote:
> 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,

It helps other distros in the ecosystem to flag patches that really
should be backported. Not everyone runs their backport trees as
agressively as a stable does.

Jason