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 09:22:32 -0800 |
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> 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()?
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!)
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