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

[Matthew Rosato <mjrosato@linux.ibm.com>]

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@linux.ibm.com>

Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>