arm64: entry: Avoid unnecessary local_irq_disable() on kernel exit

Summary

In the Linux kernel, the following vulnerability has been resolved: arm64: entry: Avoid unnecessary local_irq_disable() on kernel exit Currently, when exiting to kernel mode, we attempt involuntary preemption. The preemption logic expects IRQs to be disabled, which is why we call local_irq_disable() before attempting preemption. However, depending on the context, local_irq_disable() may be unnecessary: - __el1_irq(), the non-NMI EL1 IRQ path, already has IRQs disabled, so local_irq_disable() is redundant. - irqentry_exit_to_kernel_mode_preempt() immediately returns when exiting from an NMI-like context, so calling local_irq_disable() beforehand is unnecessary work. Furthermore, it confuses the pNMI state tracking when we are in a context with interrupts disabled and the GIC_PRIO_PSR_I_SET bit is set in the PMR, leading to a warning when CONFIG_ARM64_DEBUG_PRIORITY_MASKING=y: WARNING: ./arch/arm64/include/asm/irqflags.h:63 at arm64_exit_to_kernel_mode+0xb8/0xc0, CPU#40: retsnoop/31805 CPU: 40 UID: 0 PID: 31805 Comm: retsnoop Not tainted 7.2.0-rc6-next-20260805 #7 PREEMPTLAZY pstate: 234013c9 (nzCv DAIF +PAN -UAO +TCO +DIT +SSBS BTYPE=--) pc : arm64_exit_to_kernel_mode (arch/arm64/kernel/entry-common.c:63) lr : el1_abort (arch/arm64/kernel/entry-common.c:323) pmr: 000000f0 Call trace: arm64_exit_to_kernel_mode (arch/arm64/kernel/entry-common.c:63) (P) el1_abort (arch/arm64/kernel/entry-common.c:323) el1h_64_sync_handler (arch/arm64/kernel/entry-common.c:449) el1h_64_sync (arch/arm64/kernel/entry.S:589) [...] Split arm64_exit_to_kernel_mode() into preempt, non-preempt, and dispatch parts so that we can avoid this extra work where it is not needed and avoid breaking the pNMI tracking logic.