linux-kernel - Re: [PATCH bpf-next] uprobes: Fix the xol slots reserved for uretprobe trampoline

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Date: Thu, 20 Jun 2024 17:58:11 +0800
From: "Liao, Chang" <liaochang1@...wei.com>
To: Oleg Nesterov <oleg@...hat.com>
CC: <jolsa@...nel.org>, <rostedt@...dmis.org>, <mhiramat@...nel.org>,
	<ast@...nel.org>, <daniel@...earbox.net>, <andrii@...nel.org>,
	<nathan@...nel.org>, <peterz@...radead.org>, <mingo@...hat.com>,
	<mark.rutland@....com>, <linux-perf-users@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next] uprobes: Fix the xol slots reserved for
 uretprobe trampoline



在 2024/6/20 16:36, Oleg Nesterov 写道:
> On 06/20, Liao, Chang wrote:
>>
>> However, when i asm porting uretprobe trampoline to arm64
>> to explore its benefits on that architecture, i discovered the problem that
>> single slot is not large enought for trampoline code.
> 
> Ah, but then I'd suggest to make the changelog more clear. It looks as
> if the problem was introduced by the patch from Jiri. Note that we was
> confused as well ;)

Perhaps i should use 'RFC' in the subject line, instead of 'PATCH'?

> 
> And,
> 
> 	+	/* Reserve enough slots for the uretprobe trampoline */
> 	+	for (slot_nr = 0;
> 	+	     slot_nr < max((insns_size / UPROBE_XOL_SLOT_BYTES), 1);
> 	+	     slot_nr++)
> 
> this doesn't look right. Just suppose that insns_size = UPROBE_XOL_SLOT_BYTES + 1.
> I'd suggest DIV_ROUND_UP(insns_size, UPROBE_XOL_SLOT_BYTES).

Oh, what a stupid mistake to me. thanks for pointing that out.

> 
> And perhaps it would be better to send this change along with
> uretprobe_trampoline_for_arm64 ?

Sure, i would send them out in next revision.


> 
> Oleg.
> 

-- 
BR
Liao, Chang