Hi Alex,
On Mon, Jun 24, 2024 at 4:21 PM Alexandre Ghiti <alexgh...@rivosinc.com> wrote:
>
> We cannot delay the icache flush after patching some functions as we may
> have patched a function that will get called before the icache flush.
>
> The only way to completely avoid such scenario is by flushing the icache
> as soon as we patch a function. This will probably be costly as we don't
> batch the icache maintenance anymore.
>
> Fixes: 6ca445d8af0e ("riscv: Fix early ftrace nop patching")
> Reported-by: Conor Dooley <conor.doo...@microchip.com>
> Closes:
> https://lore.kernel.org/linux-riscv/20240613-lubricant-breath-061192a9489a@wendy/
> Signed-off-by: Alexandre Ghiti <alexgh...@rivosinc.com>
> ---
> arch/riscv/kernel/ftrace.c | 7 ++-----
> arch/riscv/kernel/patch.c | 26 ++++++++++++++++++--------
> 2 files changed, 20 insertions(+), 13 deletions(-)
>
> diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
> index 87cbd86576b2..4b95c574fd04 100644
> --- a/arch/riscv/kernel/ftrace.c
> +++ b/arch/riscv/kernel/ftrace.c
> @@ -120,9 +120,6 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace
> *rec)
> out = ftrace_make_nop(mod, rec, MCOUNT_ADDR);
> mutex_unlock(&text_mutex);
>
> - if (!mod)
> - local_flush_icache_range(rec->ip, rec->ip + MCOUNT_INSN_SIZE);
> -
> return out;
> }
>
> @@ -156,9 +153,9 @@ static int __ftrace_modify_code(void *data)
> } else {
> while (atomic_read(¶m->cpu_count) <= num_online_cpus())
> cpu_relax();
> - }
>
> - local_flush_icache_all();
> + local_flush_icache_all();
> + }
Sorry, maybe I should point it out directly earlier. But I don't think
this diff chunk is required. Threads running in the else clause from
stop_machine must not run into any patchable entry. If it runs into a
patchable entry, running the local fence.i is not going to fix the
problem.
>
> return 0;
> }
> diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
> index 4007563fb607..ab03732d06c4 100644
> --- a/arch/riscv/kernel/patch.c
> +++ b/arch/riscv/kernel/patch.c
> @@ -89,6 +89,14 @@ static int __patch_insn_set(void *addr, u8 c, size_t len)
>
> memset(waddr, c, len);
>
> + /*
> + * We could have just patched a function that is about to be
> + * called so make sure we don't execute partially patched
> + * instructions by flushing the icache as soon as possible.
> + */
> + local_flush_icache_range((unsigned long)waddr,
> + (unsigned long)waddr + len);
> +
> patch_unmap(FIX_TEXT_POKE0);
>
> if (across_pages)
> @@ -135,6 +143,14 @@ static int __patch_insn_write(void *addr, const void
> *insn, size_t len)
>
> ret = copy_to_kernel_nofault(waddr, insn, len);
>
> + /*
> + * We could have just patched a function that is about to be
> + * called so make sure we don't execute partially patched
> + * instructions by flushing the icache as soon as possible.
> + */
> + local_flush_icache_range((unsigned long)waddr,
> + (unsigned long)waddr + len);
> +
> patch_unmap(FIX_TEXT_POKE0);
>
> if (across_pages)
> @@ -189,9 +205,6 @@ int patch_text_set_nosync(void *addr, u8 c, size_t len)
>
> ret = patch_insn_set(tp, c, len);
>
> - if (!ret)
> - flush_icache_range((uintptr_t)tp, (uintptr_t)tp + len);
> -
> return ret;
> }
> NOKPROBE_SYMBOL(patch_text_set_nosync);
> @@ -224,9 +237,6 @@ int patch_text_nosync(void *addr, const void *insns,
> size_t len)
>
> ret = patch_insn_write(tp, insns, len);
>
> - if (!ret)
> - flush_icache_range((uintptr_t) tp, (uintptr_t) tp + len);
> -
> return ret;
> }
> NOKPROBE_SYMBOL(patch_text_nosync);
> @@ -253,9 +263,9 @@ static int patch_text_cb(void *data)
> } else {
> while (atomic_read(&patch->cpu_count) <= num_online_cpus())
> cpu_relax();
> - }
>
> - local_flush_icache_all();
> + local_flush_icache_all();
> + }
>
> return ret;
> }
> --
> 2.39.2
>
Thanks,
Andy
