Re: [PATCH 4/5] KVM: arm64: Unmap vLPIs affected by changes to GSI routing information

[Oliver Upton <oliver.upton@linux.dev>]

On Fri, May 23, 2025 at 01:54:01PM -0700, Sean Christopherson wrote:
> On Fri, May 23, 2025, Marc Zyngier wrote:
> > On Fri, 23 May 2025 18:48:02 +0100,
> > Sean Christopherson <seanjc@google.com> wrote:
> > > 
> > > On Fri, May 23, 2025, Marc Zyngier wrote:
> > > > > @@ -2803,6 +2804,28 @@ void kvm_arch_irq_bypass_del_producer(struct irq_bypass_consumer *cons,
> > > > >  	kvm_vgic_v4_unset_forwarding(irqfd->kvm, prod->irq);
> > > > >  }
> > > > >  
> > > > > +bool kvm_arch_irqfd_route_changed(struct kvm_kernel_irq_routing_entry *old,
> > > > > +				  struct kvm_kernel_irq_routing_entry *new)
> > > > > +{
> > > > > +	if (new->type != KVM_IRQ_ROUTING_MSI)
> > > > > +		return true;
> > > > > +
> > > > > +	return memcmp(&old->msi, &new->msi, sizeof(new->msi));
> > > > > +}
> > > > > +
> > > > > +int kvm_arch_update_irqfd_routing(struct kvm *kvm, unsigned int host_irq,
> > > > > +				  uint32_t guest_irq, bool set)
> > > > 
> > > > If we're adding this, can we take out the trash and get rid of this
> > > > 'set' parameter? Its only purpose is to be set to '1' and fed to the
> > > > x86-specific stuff. How about this:
> > > 
> > > Can we hold off on any changes to the common APIs?  Unless they're urgent and
> > > need to land in 6.16, I've got a massive series that I've been slowing working
> > > on for ~7 months that fixes this wart, and several more, e.g. gets rid of
> > > kvm_arch_irqfd_route_changed() entirely, and make the above ugliness into:
> > > 
> > > void kvm_arch_update_irqfd_routing(struct kvm_kernel_irqfd *irqfd,
> > > 				   struct kvm_kernel_irq_routing_entry *old,
> > > 				   struct kvm_kernel_irq_routing_entry *new)
> > > 
> > > 
> > > I'm ~90% confident it'll land in 6.17:
> > > https://lore.kernel.org/all/20250523010004.3240643-1-seanjc@google.com
> > 
> > Sure, if you want to preserve this fossil for another round, I don't
> > really care. But if you are planning your grand plan for 6.17, you
> > could as well rebase on top of theses patches which are aimed at -rc1
> > (yes, they are bug fixes), and it would then be perfectly acceptable
> > to have this cleanup early.
> 
> I'll be rebasing either way, so I'm not comletely opposed to it, I just don't
> see much value in rushing this particular change into 6.16 given that there's a
> bigger cleanup looming.

+1. Having a minor refactor that survives for a single kernel release is
just unnecessary churn. I imagine some folks will want to backport this
and basing the fixes series on the existing pile of crap will make that
a bit easier.

Thanks,
Oliver