Re: [RFC PATCH v3 12/15] context_tracking,x86: Defer kernel text patching IPIs

From: Peter Zijlstra
Date: Wed Nov 20 2024 - 10:17:17 EST


On Tue, Nov 19, 2024 at 04:34:59PM +0100, Valentin Schneider wrote:

> +static void __text_poke_sync(smp_cond_func_t cond_func)
> +{
> + on_each_cpu_cond(cond_func, do_sync_core, NULL, 1);
> +}
> +
> void text_poke_sync(void)
> {
> - on_each_cpu(do_sync_core, NULL, 1);
> + __text_poke_sync(NULL);
> +}
> +
> +void text_poke_sync_deferrable(void)
> +{
> + __text_poke_sync(do_sync_core_defer_cond);
> }

How about we unwrap some of that like so:

> /*
> @@ -2257,6 +2273,8 @@ static int tp_vec_nr;
> static void text_poke_bp_batch(struct text_poke_loc *tp, unsigned int nr_entries)
> {
> unsigned char int3 = INT3_INSN_OPCODE;
> + bool force_ipi = false;
> + void (*sync_fn)(void);

smp_cond_func_t cond = do_sync_core_defer_cond;

> unsigned int i;
> int do_sync;
>
> @@ -2291,11 +2309,18 @@ static void text_poke_bp_batch(struct text_poke_loc *tp, unsigned int nr_entries
> * First step: add a int3 trap to the address that will be patched.
> */
> for (i = 0; i < nr_entries; i++) {
> + /*
> + * Record that we need to send the IPI if at least one location
> + * in the batch requires it.
> + */
> + force_ipi |= tp[i].force_ipi;

if (tp[i].force_ipi)
cond = NULL;

> tp[i].old = *(u8 *)text_poke_addr(&tp[i]);
> text_poke(text_poke_addr(&tp[i]), &int3, INT3_INSN_SIZE);
> }
>
> - text_poke_sync();
> + sync_fn = force_ipi ? text_poke_sync : text_poke_sync_deferrable;
> +
> + sync_fn();

__text_poke_sync(cond);