linux-kernel - Re: [PATCH v3 bpf-next 5/7] x86/alternative: introduce text_poke

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Message-ID: <48AD9DA0-5E09-4EBD-AFF0-DA63ADA5A247@fb.com>
Date:   Tue, 11 Jan 2022 17:43:47 +0000
From:   Song Liu <songliubraving@...com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     Song Liu <song@...nel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "andrii@...nel.org" <andrii@...nel.org>,
        Kernel Team <Kernel-team@...com>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH v3 bpf-next 5/7] x86/alternative: introduce text_poke_jit



> On Jan 11, 2022, at 4:13 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> 
> On Wed, Jan 05, 2022 at 06:25:31PM -0800, Song Liu wrote:
> 
>> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
>> index 23fb4d51a5da..02c35725cc62 100644
>> --- a/arch/x86/kernel/alternative.c
>> +++ b/arch/x86/kernel/alternative.c
>> @@ -1102,6 +1102,34 @@ void *text_poke_kgdb(void *addr, const void *opcode, size_t len)
>> 	return __text_poke(addr, opcode, len);
>> }
>> 
>> +/**
>> + * text_poke_jit - Update instructions on a live kernel by jit engine
>> + * @addr: address to modify
>> + * @opcode: source of the copy
>> + * @len: length to copy, could be more than 2x PAGE_SIZE
>> + *
>> + * Only module memory taking jit text (e.g. for bpf) should be patched.
>> + */
> 
> Maybe:
> 
> 	text_poke_copy() - Copy instructions into (an unused part of) RX memory
> 	@args...
> 
> 	Not safe against concurrent execution; useful for JITs to dump
> 	new code blocks into unused regions of RX memory. Can be used in
> 	conjunction with synchronize_rcu_tasks() to wait for existing
> 	execution to quiesce after having made sure no existing
> 	functions pointers are life.
> 
> or something along those lines?

This sounds good! Thanks!

Song