Merge tag 'x86-core-2025-12-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull core x86 updates from Ingo Molnar:

 - x86/alternatives: Drop unnecessary test after call to
   alt_replace_call() (Juergen Gross)

 - x86/dumpstack: Prevent KASAN false positive warnings in
   __show_regs() (Tengda Wu)

* tag 'x86-core-2025-12-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/dumpstack: Prevent KASAN false positive warnings in __show_regs()
  x86/alternative: Drop not needed test after call of alt_replace_call()

Author: torvalds

arch/x86/kernel/alternative.c

@@ -541,7 +541,7 @@ EXPORT_SYMBOL(BUG_func);
  * Rewrite the "call BUG_func" replacement to point to the target of the
  * indirect pv_ops call "call *disp(%ip)".
  */
-static int alt_replace_call(u8 *instr, u8 *insn_buff, struct alt_instr *a)
+static unsigned int alt_replace_call(u8 *instr, u8 *insn_buff, struct alt_instr *a)
 {
 	void *target, *bug = &BUG_func;
 	s32 disp;
@@ -625,7 +625,7 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
 	 * order.
 	 */
 	for (a = start; a < end; a++) {
-		int insn_buff_sz = 0;
+		unsigned int insn_buff_sz = 0;
 
 		/*
 		 * In case of nested ALTERNATIVE()s the outer alternative might
@@ -665,11 +665,8 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
 		memcpy(insn_buff, replacement, a->replacementlen);
 		insn_buff_sz = a->replacementlen;
 
-		if (a->flags & ALT_FLAG_DIRECT_CALL) {
+		if (a->flags & ALT_FLAG_DIRECT_CALL)
 			insn_buff_sz = alt_replace_call(instr, insn_buff, a);
-			if (insn_buff_sz < 0)
-				continue;
-		}
 
 		for (; insn_buff_sz < a->instrlen; insn_buff_sz++)
 			insn_buff[insn_buff_sz] = 0x90;

arch/x86/kernel/dumpstack.c

@@ -181,8 +181,8 @@ static void show_regs_if_on_stack(struct stack_info *info, struct pt_regs *regs,
  * in false positive reports. Disable instrumentation to avoid those.
  */
 __no_kmsan_checks
-static void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,
-			unsigned long *stack, const char *log_lvl)
+static void __show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,
+				 unsigned long *stack, const char *log_lvl)
 {
 	struct unwind_state state;
 	struct stack_info stack_info = {0};
@@ -303,6 +303,25 @@ static void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,
 	}
 }
 
+static void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,
+			       unsigned long *stack, const char *log_lvl)
+{
+	/*
+	 * Disable KASAN to avoid false positives during walking another
+	 * task's stacks, as values on these stacks may change concurrently
+	 * with task execution.
+	 */
+	bool disable_kasan = task && task != current;
+
+	if (disable_kasan)
+		kasan_disable_current();
+
+	__show_trace_log_lvl(task, regs, stack, log_lvl);
+
+	if (disable_kasan)
+		kasan_enable_current();
+}
+
 void show_stack(struct task_struct *task, unsigned long *sp,
 		       const char *loglvl)
 {