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.

Reported-by: Breno Leitao <leitao@debian.org>
Fixes: ae654112eac0 ("arm64: entry: Use split preemption logic")
Link: https://lore.kernel.org/all/20260807-arm64_fix-v1-1-d069ccf9d71b@debian.org/
Reviewed-by: Jinjie Ruan <ruanjinjie@huawei.com>
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>

0 files changed, 0 insertions, 0 deletions