FAILED: Patch "x86/traps: move kmsan check after instrumentation_begin" failed to apply to v6.1-stable tree

The patch below does not apply to the v6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From 1db272864ff250b5e607283eaec819e1186c8e26 Mon Sep 17 00:00:00 2001
From: Sabyrzhan Tasbolatov <[email protected]>
Date: Wed, 16 Oct 2024 20:24:07 +0500
Subject: [PATCH] x86/traps: move kmsan check after instrumentation_begin

During x86_64 kernel build with CONFIG_KMSAN, the objtool warns following:

  AR      built-in.a
  AR      vmlinux.a
  LD      vmlinux.o

vmlinux.o: warning: objtool: handle_bug+0x4: call to
kmsan_unpoison_entry_regs() leaves .noinstr.text section
OBJCOPY modules.builtin.modinfo
GEN modules.builtin
MODPOST Module.symvers
CC .vmlinux.export.o

Moving kmsan_unpoison_entry_regs() _after_ instrumentation_begin() fixes the warning.

There is decode_bug(regs->ip, &imm) is left before KMSAN unpoisoining, but it has the return condition and if we include it after instrumentation_begin() it results the warning "return with instrumentation enabled", hence, I'm concerned that regs will not be KMSAN unpoisoned if ud_type == BUG_NONE is true.

---
 arch/x86/kernel/traps.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

index d05392db5d0fe..2dbadf347b5f4 100644
@@ -261,12 +261,6 @@ static noinstr bool handle_bug(struct pt_regs *regs)
 	int ud_type;
 	u32 imm;
 
-	/*
-	 * Normally @regs are unpoisoned by irqentry_enter(), but handle_bug()
-	 * is a rare case that uses @regs without passing them to
-	 * irqentry_enter().
-	 */
-	kmsan_unpoison_entry_regs(regs);
 	ud_type = decode_bug(regs->ip, &imm);
 	if (ud_type == BUG_NONE)
 		return handled;

@@ -275,6 +269,12 @@ static noinstr bool handle_bug(struct pt_regs *regs)
 	 * All lies, just get the WARN/BUG out.
 	 */
 	instrumentation_begin();
+	/*
+	 * Normally @regs are unpoisoned by irqentry_enter(), but handle_bug()
+	 * is a rare case that uses @regs without passing them to
+	 * irqentry_enter().
+	 */
+	kmsan_unpoison_entry_regs(regs);
 	/*
 	 * Since we're emulating a CALL with exceptions, restore the interrupt
 	 * state to what it was at the exception site.

2.43.0