Re: [PATCH 4.14 1/2] genirq/affinity: Handle affinity setting on inactive interrupts correctly

[Greg KH <greg@kroah.com>]

On Wed, Aug 19, 2020 at 04:05:51PM +0000, Frank van der Linden wrote:
> On Wed, Aug 19, 2020 at 11:55:37AM +0200, Greg KH wrote:
> > On Mon, Aug 10, 2020 at 08:11:43PM +0000, Frank van der Linden wrote:
> > > From: Thomas Gleixner <tglx@linutronix.de>
> > >
> > > commit baedb87d1b53532f81b4bd0387f83b05d4f7eb9a upstream.
> > >
> > > Setting interrupt affinity on inactive interrupts is inconsistent when
> > > hierarchical irq domains are enabled. The core code should just store the
> > > affinity and not call into the irq chip driver for inactive interrupts
> > > because the chip drivers may not be in a state to handle such requests.
> > >
> > > X86 has a hacky workaround for that but all other irq chips have not which
> > > causes problems e.g. on GIC V3 ITS.
> > >
> > > Instead of adding more ugly hacks all over the place, solve the problem in
> > > the core code. If the affinity is set on an inactive interrupt then:
> > >
> > >     - Store it in the irq descriptors affinity mask
> > >     - Update the effective affinity to reflect that so user space has
> > >       a consistent view
> > >     - Don't call into the irq chip driver
> > >
> > > This is the core equivalent of the X86 workaround and works correctly
> > > because the affinity setting is established in the irq chip when the
> > > interrupt is activated later on.
> > >
> > > Note, that this is only effective when hierarchical irq domains are enabled
> > > by the architecture. Doing it unconditionally would break legacy irq chip
> > > implementations.
> > >
> > > For hierarchial irq domains this works correctly as none of the drivers can
> > > have a dependency on affinity setting in inactive state by design.
> > >
> > > Remove the X86 workaround as it is not longer required.
> > >
> > > Fixes: 02edee152d6e ("x86/apic/vector: Ignore set_affinity call for inactive interrupts")
> > 
> > Why is this needed for 4.14.y, when this "Fixes:" tag says a commit that
> > showed up in 4.15?
> 
> The issue of set_affinity being called on inactive interrupts, and it
> not being handled correctly, was already there in 4.14. The commit in
> the Fixes: tag is the x86 workaround, which came in in 4.15, and is
> no longer needed.
> 
> So we still need the backport of the genirq changes, to fix it in 4.14.
> This is mostly for arm64 (gicv3), where this issue results in interrupts
> getting messed up.

Ok, thanks, both now queued up.

greg k-h