Re: [PATCH v5 5/6] kprobes: Use text_alloc() and text_free()

[Jarkko Sakkinen]

On Fri, Jul 24, 2020 at 11:27:46AM +0200, Ingo Molnar wrote:
> 
> * Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx> wrote:
> 
> > Use text_alloc() and text_free() instead of module_alloc() and
> > module_memfree() when an arch provides them.
> > 
> > Cc: linux-mm@xxxxxxxxx
> > Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> > Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
> > ---
> >  kernel/kprobes.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> > 
> > diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> > index 4e46d96d4e16..611fcda9f6bf 100644
> > --- a/kernel/kprobes.c
> > +++ b/kernel/kprobes.c
> > @@ -40,6 +40,7 @@
> >  #include <asm/cacheflush.h>
> >  #include <asm/errno.h>
> >  #include <linux/uaccess.h>
> > +#include <linux/vmalloc.h>
> >  
> >  #define KPROBE_HASH_BITS 6
> >  #define KPROBE_TABLE_SIZE (1 << KPROBE_HASH_BITS)
> > @@ -111,12 +112,20 @@ enum kprobe_slot_state {
> >  
> >  void __weak *alloc_insn_page(void)
> >  {
> > +#ifdef CONFIG_ARCH_HAS_TEXT_ALLOC
> > +	return text_alloc(PAGE_SIZE);
> > +#else
> >  	return module_alloc(PAGE_SIZE);
> > +#endif
> >  }
> >  
> >  void __weak free_insn_page(void *page)
> >  {
> > +#ifdef CONFIG_ARCH_HAS_TEXT_ALLOC
> > +	text_free(page);
> > +#else
> >  	module_memfree(page);
> > +#endif
> >  }
> 
> I've read the observations in the other threads, but this #ifdef 
> jungle is silly, it's a de-facto open coded text_alloc() with a 
> module_alloc() fallback...

In the previous version I had:

  https://lore.kernel.org/lkml/20200717030422.679972-4-jarkko.sakkinen@xxxxxxxxxxxxxxx/

and I had just calls to text_alloc() and text_free() in corresponding
snippet to the above.

I got this feedback from Mike:

  https://lore.kernel.org/lkml/20200718162359.GA2919062@xxxxxxxxxx/

I'm not still sure that I fully understand this feedback as I don't see
any inherent and obvious difference to the v4. In that version fallbacks
are to module_alloc() and module_memfree() and text_alloc() and
text_memfree() can be overridden by arch.

> Thanks,
> 
> 	Ingo

/Jarkko