Messages in this thread | | | Date | Wed, 26 Oct 2022 09:02:47 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 4/5] x86/ftrace: Remove SYSTEM_BOOTING exceptions |
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On Tue, Oct 25, 2022 at 04:59:56PM -0400, Steven Rostedt wrote: > On Tue, 25 Oct 2022 22:07:00 +0200 > Peter Zijlstra <peterz@infradead.org> wrote: > > > Now that text_poke is available before ftrace, remove the > > SYSTEM_BOOTING exceptions. > > > > Specifically, this cures a W+X case during boot. > > We have W+X all over the place (the entire kernel text). And I don't think > we really want this. > > This will slow down boots in general, as it will cause all static_branches > to use this memory page logic. And I don't think we really want to do > that at boot up when we don't need to.
Both static_call and jump_label explicitly call text_poke_early() when appropriate.
> I would change this to: > > if (unlikely(system_state == SYSTEM_BOOTING) && > core_kernel_text((unsigned long)addr)) { > > This way we still do memcpy() on all core kernel text which is still > writable. It was the ftrace allocated trampoline that caused issues, not > the locations that were being updated.
I would suggest changing ftrace to call text_poke_early() when appropriate if it matters (it already does a little of that); doing a boot test with and without my patch 4 on shows no noticable overhead over being horribly slow either way.
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