The following commit has been merged into the x86/alternatives branch of tip:
Commit-ID: d60e4b2410e1b9f7c5ca347c78c6b07175c2e873
Gitweb: https://git.kernel.org/tip/d60e4b2410e1b9f7c5ca347c78c6b07175c2e873
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Fri, 11 Apr 2025 07:40:14 +02:00
Committer: Ingo Molnar <mingo@kernel.org>
CommitterDate: Fri, 11 Apr 2025 11:01:33 +02:00
x86/alternatives: Document the text_poke_bp_batch() synchronization rules a bit more
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Juergen Gross <jgross@suse.com>
Cc: "H . Peter Anvin" <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20250411054105.2341982-3-mingo@kernel.org
---
arch/x86/kernel/alternative.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 85089c7..5f44814 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -2751,6 +2751,13 @@ static void text_poke_bp_batch(struct text_poke_loc *tp, unsigned int nr_entries
/*
* Remove and wait for refs to be zero.
+ *
+ * Notably, if after step-3 above the INT3 got removed, then the
+ * text_poke_sync() will have serialized against any running INT3
+ * handlers and the below spin-wait will not happen.
+ *
+ * IOW. unless the replacement instruction is INT3, this case goes
+ * unused.
*/
for_each_possible_cpu(i) {
atomic_t *refs = per_cpu_ptr(&bp_refs, i);