[PATCH v3 21/22] x86/int3: Avoid atomic instrumentation

Peter Zijlstra
2020-02-19T15:14:37Z

Use arch_atomic_*() and READ_ONCE_NOCHECK() to ensure nothing untoward
creeps in and ruins things.

That is; this is the INT3 text poke handler, strictly limit the code
that runs in it, lest we inadvertenly hit yet another INT3.

Reported-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/kernel/alternative.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -960,9 +960,9 @@ static struct bp_patching_desc *bp_desc;
static __always_inline
struct bp_patching_desc *try_get_desc(struct bp_patching_desc **descp)
{
- struct bp_patching_desc *desc = READ_ONCE(*descp); /* rcu_dereference */
+ struct bp_patching_desc *desc = READ_ONCE_NOCHECK(*descp); /* rcu_dereference */

- if (!desc || !atomic_inc_not_zero(&desc->refs))
+ if (!desc || !arch_atomic_inc_not_zero(&desc->refs))
return NULL;

return desc;
@@ -971,7 +971,7 @@ struct bp_patching_desc *try_get_desc(st
static __always_inline void put_desc(struct bp_patching_desc *desc)
{
smp_mb__before_atomic();
- atomic_dec(&desc->refs);
+ arch_atomic_dec(&desc->refs);
}

static __always_inline void *text_poke_addr(struct text_poke_loc *tp)