Re: [PATCH v9 3/3] KVM: s390: Introducing kvm_arch_set_irq_inatomic fast inject

[Douglas Freimuth]

On 6/2/26 1:30 PM, Matthew Rosato wrote:
> On 5/31/26 3:03 PM, Douglas Freimuth wrote:
> > s390 needs a fast path for irq injection, and along those lines we
> > introduce kvm_arch_set_irq_inatomic. Instead of placing all interrupts on
> > the global work queue as it does today, this patch provides a fast path for
> > irq injection.
> >
> > The inatomic fast path cannot lose control since it is running with
> > interrupts disabled. This meant making the following changes that exist on
> > the slow path today. First, the adapter_indicators page needs to be mapped
> > since it is accessed with interrupts disabled, so we added map/unmap
> > functions. Second, access to shared resources between the fast and slow
> > paths needed to be changed from mutex and semaphores to spin_lock's.
> > Finally, the memory allocation on the slow path utilizes GFP_KERNEL_ACCOUNT
> > but we had to implement the fast path with GFP_ATOMIC allocation. Each of
> > these enhancements were required to prevent blocking on the fast inject
> > path.
> >
> > Fencing of Fast Inject in Secure Execution environments is enabled in the
> > patch series by not mapping adapter indicator pages. In Secure Execution
> > environments the path of execution available before this patch is followed.
> >
> > Statistical counters have been added to enable analysis of irq injection on
> > the fast path and slow path including io_390_inatomic, io_flic_inject_airq,
> > io_set_adapter_int and io_390_inatomic_no_inject. The no inject counter
> > captures adapter masked, coalesced and suppressed interrupts.
> >
> > Signed-off-by: Douglas Freimuth <freimuth@xxxxxxxxxxxxx>
>
> Reviewed-by: Matthew Rosato <mjrosato@xxxxxxxxxxxxx>

Matt, thank you for all of your inputs across the iterations.>