From 39aebe0e89469c2904e60b1e977e0d4dbf33326b Mon Sep 17 00:00:00 2001 From: Vladimir Murzin Date: Mon, 27 Jul 2026 17:34:17 +0100 Subject: [PATCH] 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 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 Signed-off-by: Vladimir Murzin Signed-off-by: Will Deacon --- arch/arm64/kernel/entry-common.c | 30 +++++++++++++++++++++++++----- 1 file changed, 25 insertions(+), 5 deletions(-) diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c index 2be42d7f4eaa..72c03ccea59f 100644 --- a/arch/arm64/kernel/entry-common.c +++ b/arch/arm64/kernel/entry-common.c @@ -52,16 +52,36 @@ static noinstr irqentry_state_t arm64_enter_from_kernel_mode(struct pt_regs *reg * After this function returns it is not safe to call regular kernel code, * instrumentable code, or any code which may trigger an exception. */ -static void noinstr arm64_exit_to_kernel_mode(struct pt_regs *regs, - irqentry_state_t state) +static void noinstr __arm64_exit_to_kernel_mode(struct pt_regs *regs, + irqentry_state_t state) { - local_irq_disable(); - irqentry_exit_to_kernel_mode_preempt(regs, state); local_daif_mask(); mte_check_tfsr_exit(); irqentry_exit_to_kernel_mode_after_preempt(regs, state); } +/* + * We are returning from the context which allows involuntary kernel preemption + */ +static void noinstr arm64_exit_to_kernel_mode_preempt(struct pt_regs *regs, + irqentry_state_t state) +{ + irqentry_exit_to_kernel_mode_preempt(regs, state); + __arm64_exit_to_kernel_mode(regs, state); +} + +static void noinstr arm64_exit_to_kernel_mode(struct pt_regs *regs, + irqentry_state_t state) +{ + if (!regs_irqs_disabled(regs)) { + local_irq_disable(); + arm64_exit_to_kernel_mode_preempt(regs, state); + return; + } + + __arm64_exit_to_kernel_mode(regs, state); +} + static __always_inline void arm64_syscall_enter_from_user_mode(struct pt_regs *regs) { enter_from_user_mode(regs); @@ -510,7 +530,7 @@ static __always_inline void __el1_irq(struct pt_regs *regs, do_interrupt_handler(regs, handler); irq_exit_rcu(); - arm64_exit_to_kernel_mode(regs, state); + arm64_exit_to_kernel_mode_preempt(regs, state); } static void noinstr el1_interrupt(struct pt_regs *regs, void (*handler)(struct pt_regs *))