[PATCH v2 RESEND 1/2] ARM: spectre-v2: Fix potential missing mitigations

[Sebastian Andrzej Siewior]

On 2025-10-28 17:20:06 [+0100], To Xie Yuanbin wrote:
> The requirement is to invoke the mitigation callback of the right CPU.
> What about disabling preemption before getting the callback and doing
> the invocation?

Something like this:

diff --git a/arch/arm/include/asm/system_misc.h b/arch/arm/include/asm/system_misc.h
--- a/arch/arm/include/asm/system_misc.h
+++ b/arch/arm/include/asm/system_misc.h
@@ -20,8 +20,10 @@ typedef void (*harden_branch_predictor_fn_t)(void);
 DECLARE_PER_CPU(harden_branch_predictor_fn_t, harden_branch_predictor_fn);
 static inline void harden_branch_predictor(void)
 {
-	harden_branch_predictor_fn_t fn = per_cpu(harden_branch_predictor_fn,
-						  smp_processor_id());
+	harden_branch_predictor_fn_t fn;
+
+	guard(preempt)();
+	fn = per_cpu(harden_branch_predictor_fn, smp_processor_id());
 	if (fn)
 		fn();
 }

Sebastian