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

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Date: Thu, 20 Jun 2024 19:58:06 +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 18:52, Oleg Nesterov 写道:
> On 06/20, Liao, Chang wrote:
>>
>> 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'?
> 
> Well. IMO the changelog should explain that the current code is correct,
> but you are going to change arm64 and arch_uprobe_trampoline(psize) on
> arm64 can return with *psize > UPROBE_XOL_SLOT_BYTES.

You are absolutely right, Here is a draft of the revised changelog for your
suggestion:

    uprobes: Adjust the xol slots reserved for the uretprobe trampoline on arm64

    Adjust ixol slots reservation logic to ensure to accommodate the uretprobe
    trampoline on arm64, which is potentailly larger than single xol slot. This
    ensure the trampoline code fis within the reserved memory and avoids potential
    errors.

> 
> Oleg.
> 
> 

-- 
BR
Liao, Chang