Messages in this thread | | | Date | Fri, 6 Mar 2009 14:15:17 -0500 | From | Mathieu Desnoyers <> | Subject | Re: [PATCH -tip 4/4] Atomic text_poke() with fixmap take2 |
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* Ingo Molnar (mingo@elte.hu) wrote: > > * Masami Hiramatsu <mhiramat@redhat.com> wrote: > > > @@ -523,14 +526,17 @@ void *__kprobes text_poke(void *addr, co > > pages[1] = virt_to_page(addr + PAGE_SIZE); > > } > > BUG_ON(!pages[0]); > > - if (!pages[1]) > > - nr_pages = 1; > > - vaddr = vmap(pages, nr_pages, VM_MAP, PAGE_KERNEL); > > - BUG_ON(!vaddr); > > - local_irq_disable(); > > + local_irq_save(flags); > > + set_fixmap(FIX_TEXT_POKE0, page_to_phys(pages[0])); > > + if (pages[1]) > > + set_fixmap(FIX_TEXT_POKE1, page_to_phys(pages[1])); > > + vaddr = (char *)fix_to_virt(FIX_TEXT_POKE0); > > memcpy(&vaddr[(unsigned long)addr & ~PAGE_MASK], opcode, len); > > - local_irq_enable(); > > - vunmap(vaddr); > > + clear_fixmap(FIX_TEXT_POKE0); > > + if (pages[1]) > > + clear_fixmap(FIX_TEXT_POKE1); > > + local_flush_tlb(); > > + local_irq_restore(flags); > > sync_core(); > > I'm not sure at all about this widening of the irq-atomic > section and the idea of allowing non-locked access on single-CPU > situations - we dont really want to micro-optimize any of this > on such a level, holding the text lock is a robust rule all code > should be listening to. (Creating locking assymetry always > inserts a certain amount of fragility - adding to an already > fragile concept here.) > > And note that there's no reason why text_poke could not be used > in stop_machine_run() - the stop_machine_run() handler must not > take the text_lock of course - but outside code calling > stop_machine_run() can do it and can hence serialize properly. > > Note that even if we did this then your v2 patch is not fully > correct: you need to move the sync_core() at the end of the > sequence inside the critical section too. (right now this is > mostly harmless because the INVLPG inside the clear_fixmap() > happens to be serializing so it has an implicit sync_core() > property - but nevertheless we better do this straight away to > not cause problems later down the line.) > > Ingo
Agreed. The alternatives_smp_lock/alternatives_smp_unlock specific case does not bring us much if it has no perceivable performance impact. It's better to keep a standard interface and clear requirements.
Mathieu
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