[RFC PATCH] uprobes: copy to user-space xol page with proper cache flushing

[Linus Torvalds]

On Fri, Apr 11, 2014 at 11:02 AM, David Miller <davem at davemloft.net> wrote:
>
> It's not enough, we need to have the 'mm' so we can know what cpu's this
> address space has executed upon, and therefore what cpus need the broadcast
> flush.

Ok. But still, it shouldn't need "vma".

> See my other reply, we can just make a __copy_to_user_page() that takes 'mm'
> and a boolean 'executable' which uprobes can unconditionally pass as true.

Sure, that doesn't look disgusting. That said, I thought at least one
architecture (powerpc) did more than just check the executable bit: I
think somebody actually does a page-per-page "has this been mapped
executably" thing because their icache flush is *so* expensive. So
that boolean "executable" bit is potentially architecture-specific.

And quite frankly, using the "vma->vm_flags" sounds potentially
*incorrect* to me, since it really isn't about the vma. If you change
a page through a non-executable vma, you'd want to flush the icache
entry for that page mapped in a totally different vma. So I really get
the feeling that passing in "vma" is actively *wrong*. The vma
interface really makes little to no sense.

Hmm?

            Linus