On 04/09, Jiri Olsa wrote:
>
> > Just it looks a bit strange to me. Even if we do not have a use-case
> > for other nops, why we can't emulate them all just for consistency?
>
> we can, I went with nop5 just for simplicity, if you think
> having all nops support is better, let's do that
Well... Let me repeat, I am not really arguing and I do not want to delay
your next changes. We can always cleanup this code later. Please see below.
> I checked and compact process executes 64bit nops just fine,
> so we should be ok there
OK. Then, for your original patch:
Acked-by: Oleg Nesterov <o...@redhat.com>
I'd only ask to define is_nop5_insn/emulate_nop5_insn regardless of
CONFIG_X86_64. I understand that we have no reason to emulate nop5
on the 32-bit kernel, but at the same time I don't see any reason to
complicate this code to explicitly "nack" nop5 in this case.
As for the new version below:
> --- a/arch/x86/kernel/uprobes.c
> +++ b/arch/x86/kernel/uprobes.c
> @@ -840,12 +840,16 @@ static int branch_setup_xol_ops(struct arch_uprobe
> *auprobe, struct insn *insn)
> insn_byte_t p;
> int i;
>
> + /* x86_nops[i]; same as jmp with .offs = 0 */
> + for (i = 1; i <= ASM_NOP_MAX; ++i) {
> + if (!memcmp(insn->kaddr, x86_nops[i], i))
> + goto setup;
> + }
Well, yes, I'd personally obviously prefer this version ;) Just because
it looks a bit more clear/consistent to me. But this is subjective.
And,
> - case 0x90: /* prefix* + nop; same as jmp with .offs = 0 */
> - goto setup;
No, this is wrong. Please see my reply to myself,
https://lore.kernel.org/all/20250409114950.gb32...@redhat.com/
This way we can no longer emulate, say, "rep; nop". Exactly because
either way memcmp(x86_nops[i]) checks the whole instruction.
Probably we don't really care, but still this patch shouldn't add any
"regression".
So, let me repeat. Up to you. Whatever you prefer. I just tried to
understand your patch.
You have my ACK in any case.
Oleg.
