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SubjectRe: [PATCH 2/5] ftrace, x86: make kernel text writable only for conversions

* Steven Rostedt <rostedt@goodmis.org> wrote:

> > > +/* used by ftrace */
> > > +void set_kernel_text_rw(void)
> >
> > i'd leave out the 'used by ftrace' bit - more uses might
> > arise. How does kprobes get around readonly pages, it uses
> > these APIs too, right?
>
> kprobes uses text_poke. text_poke uses vmap to create its own
> page table pointers to the text memory, does the modification
> and then removes the pointers. This is quite heavy weight and
> since ftrace needs to modify 10s of thousands of areas,
> converting all of kernel text page tables is much more
> efficient.
>
> Note, if kprobes did change the original page tables, then it
> too would have hit the split_large_page bug too.

i think the real reason is that kprobes was written before we
had this more flexible and more usable CPA code.

Ingo


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