Messages in this thread | | | Subject | Re: [PATCH v3 2/7] x86/jump_label: Use text_poke_early() during early_init | From | Andy Lutomirski <> | Date | Mon, 5 Nov 2018 11:03:49 -0800 |
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> On Nov 5, 2018, at 9:49 AM, Nadav Amit <namit@vmware.com> wrote: > > From: Andy Lutomirski > Sent: November 5, 2018 at 5:22:32 PM GMT >> To: Peter Zijlstra <peterz@infradead.org> >> Cc: Nadav Amit <namit@vmware.com>, Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org, x86@kernel.org, H. Peter Anvin <hpa@zytor.com>, Thomas Gleixner <tglx@linutronix.de>, Borislav Petkov <bp@alien8.de>, Dave Hansen <dave.hansen@linux.intel.com>, Andy Lutomirski <luto@kernel.org>, Kees Cook <keescook@chromium.org>, Dave Hansen <dave.hansen@intel.com>, Masami Hiramatsu <mhiramat@kernel.org> >> Subject: Re: [PATCH v3 2/7] x86/jump_label: Use text_poke_early() during early_init >> >> >> >>>> On Nov 5, 2018, at 6:09 AM, Peter Zijlstra <peterz@infradead.org> wrote: >>>> >>>> On Fri, Nov 02, 2018 at 04:29:41PM -0700, Nadav Amit wrote: >>>> diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c >>>> index aac0c1f7e354..367c1d0c20a3 100644 >>>> --- a/arch/x86/kernel/jump_label.c >>>> +++ b/arch/x86/kernel/jump_label.c >>>> @@ -52,7 +52,13 @@ static void __ref __jump_label_transform(struct jump_entry *entry, >>>> jmp.offset = jump_entry_target(entry) - >>>> (jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE); >>>> >>>> - if (early_boot_irqs_disabled) >>>> + /* >>>> + * As long as we are in early boot, we can use text_poke_early(), which >>>> + * is more efficient: the memory was still not marked as read-only (it >>>> + * is only marked after poking_init()). This also prevents us from using >>>> + * text_poke() before poking_init() is called. >>>> + */ >>>> + if (!early_boot_done) >>>> poker = text_poke_early; >>>> >>>> if (type == JUMP_LABEL_JMP) { >>> >>> It took me a while to untangle init/maze^H^Hin.c... but I think this >>> is all we need: >>> >>> diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c >>> index aac0c1f7e354..ed5fe274a7d8 100644 >>> --- a/arch/x86/kernel/jump_label.c >>> +++ b/arch/x86/kernel/jump_label.c >>> @@ -52,7 +52,12 @@ static void __ref __jump_label_transform(struct jump_entry *entry, >>> jmp.offset = jump_entry_target(entry) - >>> (jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE); >>> >>> - if (early_boot_irqs_disabled) >>> + /* >>> + * As long as we're UP and not yet marked RO, we can use >>> + * text_poke_early; SYSTEM_BOOTING guarantees both, as we switch to >>> + * SYSTEM_SCHEDULING before going either. >>> + */ >>> + if (system_state == SYSTEM_BOOTING) >>> poker = text_poke_early; >>> >>> if (type == JUMP_LABEL_JMP) { >> >> Can we move this logic into text_poke() and get rid of text_poke_early()? > > This will negatively affect poking of modules doing module loading, e.g., > apply_paravirt(). This can be resolved by keeping track when the module is > write-protected and giving a module parameter to text_poke(). Does it worth > the complexity?
Probably not.
OTOH, why does alternative patching need text_poke() at all? Can’t it just write to the text?
> >> FWIW, alternative patching was, at some point, a significant fraction of >> total boot time in some cases. This was probably mostly due to unnecessary >> sync_core() calls. Although I think this was reported on a VM, and >> sync_core() used to be *extremely* expensive on a VM, but that’s fixed >> now, and it even got backported, I think. >> >> (Hmm. Maybe we can also make jump label patching work in early boot, too!) > > It may be possible to resolve the dependencies between poking_init() and the > other *_init(). I first considered doing that, yet, it makes the code very > fragile, and I don’t see the value in getting rid of text_poke_early() from > security or simplicity point of views. Let me know if you think otherwise. > > Regards, > Nadav
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