linux-kernel - Re: [RFC PATCH] text_poke/ftrace/x86: Allow text

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Message-ID: <CAHk-=wj_jxetFqMB8VWcJdtOt+CU0r_isyGV4AhEYFxA7YsU7Q@mail.gmail.com>
Date:   Mon, 24 Oct 2022 18:02:32 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        Linux Trace Kernel <linux-trace-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        linux-arch@...r.kernel.org
Subject: Re: [RFC PATCH] text_poke/ftrace/x86: Allow text_poke() to be called
 in early boot

On Mon, Oct 24, 2022 at 5:21 PM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> It's all about updating read only pages that are executable with a shadow mm.

Right. And it doesn't actually need the mm at all, all it wants is the
kernel page tables. Which is why all the "dup_mmap()" stuff seems so
wrong.

I suspect mm_alloc() does everything that VM actually needs.

IOW, it shouldn't have used the fork() helper, it should have used the
execve() helper that actually starts out from a clean slate. Because a
clean slate is exactly what that code wants.

No?

           Linus