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From:   Song Liu <song@kernel.org>
Date:   Sat, 17 Jun 2023 09:38:17 -0700
Message-ID: <CAPhsuW4KDriCDfQ40MKKQ3AjyeRbEUJxjqoBLipe5AJMxY3U-w@mail.gmail.com>
Subject: Re: [PATCH v2 07/12] arm64, execmem: extend execmem_params for
 generated code definitions
To:     Kent Overstreet <kent.overstreet@linux.dev>
Cc:     Mike Rapoport <rppt@kernel.org>, linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
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On Sat, Jun 17, 2023 at 8:37=E2=80=AFAM Kent Overstreet
<kent.overstreet@linux.dev> wrote:
>
> On Sat, Jun 17, 2023 at 09:57:59AM +0300, Mike Rapoport wrote:
> > > This is growing fast. :) We have 3 now: text, data, jit. And it will =
be
> > > 5 when we split data into rw data, ro data, ro after init data. I won=
der
> > > whether we should still do some type enum here. But we can revisit
> > > this topic later.
> >
> > I don't think we'd need 5. Four at most :)
> >
> > I don't know yet what would be the best way to differentiate RW and RO
> > data, but ro_after_init surely won't need a new type. It either will be
> > allocated as RW and then the caller will have to set it RO after
> > initialization is done, or it will be allocated as RO and the caller wi=
ll
> > have to do something like text_poke to update it.
>
> Perhaps ro_after_init could use the same allocation interface and share
> pages with ro pages - if we just added a refcount for "this page
> currently needs to be rw, module is still loading?"

If we don't relax rules with read only, we will have to separate rw, ro,
and ro_after_init. But we can still have page sharing:

Two modules can put rw data on the same page.
With text poke (ro data poke to be accurate), two modules can put
ro data on the same page.

> text_poke() approach wouldn't be workable, you'd have to audit and fix
> all module init code in the entire kernel.

Agreed. For this reason, each module has to have its own page(s) for
ro_after_init data.

To eventually remove VM_FLUSH_RESET_PERMS, we want
ro_after_init data to share the same allocation interface.

Thanks,
Song