linux-kernel - Re: [PATCH v3 1/6] x86/alternatives: Teach text_poke

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Message-ID: <b72b9c83-154e-010d-d8c2-3e163073426d@redhat.com>
Date:   Wed, 9 Oct 2019 14:03:16 +0200
From:   Daniel Bristot de Oliveira <bristot@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>, x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, rostedt@...dmis.org,
        mhiramat@...nel.org, jbaron@...mai.com,
        torvalds@...ux-foundation.org, tglx@...utronix.de,
        mingo@...nel.org, namit@...are.com, hpa@...or.com, luto@...nel.org,
        ard.biesheuvel@...aro.org, jpoimboe@...hat.com
Subject: Re: [PATCH v3 1/6] x86/alternatives: Teach text_poke_bp() to emulate
 instructions

On 07/10/2019 10:17, Peter Zijlstra wrote:
> In preparation for static_call and variable size jump_label support,
> teach text_poke_bp() to emulate instructions, namely:
> 
>   JMP32, JMP8, CALL, NOP2, NOP_ATOMIC5, INT3
> 
> The current text_poke_bp() takes a @handler argument which is used as
> a jump target when the temporary INT3 is hit by a different CPU.
> 
> When patching CALL instructions, this doesn't work because we'd miss
> the PUSH of the return address. Instead, teach poke_int3_handler() to
> emulate an instruction, typically the instruction we're patching in.
> 
> This fits almost all text_poke_bp() users, except
> arch_unoptimize_kprobe() which restores random text, and for that site
> we have to build an explicit emulate instruction.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Reviewed-by: Masami Hiramatsu <mhiramat@...nel.org>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Daniel Bristot de Oliveira <bristot@...hat.com>

Reviewed-by: Daniel Bristot de Oliveira <bristot@...hat.com>

Thanks!
-- Daniel