netdev - Re: [PATCH v2 07/12] arm64, execmem: extend execmem

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Date: Sat, 17 Jun 2023 09:38:17 -0700
From: Song Liu <song@...nel.org>
To: Kent Overstreet <kent.overstreet@...ux.dev>
Cc: Mike Rapoport <rppt@...nel.org>, linux-kernel@...r.kernel.org, 
	Andrew Morton <akpm@...ux-foundation.org>, Catalin Marinas <catalin.marinas@....com>, 
	Christophe Leroy <christophe.leroy@...roup.eu>, "David S. Miller" <davem@...emloft.net>, 
	Dinh Nguyen <dinguyen@...nel.org>, Heiko Carstens <hca@...ux.ibm.com>, Helge Deller <deller@....de>, 
	Huacai Chen <chenhuacai@...nel.org>, Luis Chamberlain <mcgrof@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, Michael Ellerman <mpe@...erman.id.au>, 
	Nadav Amit <nadav.amit@...il.com>, "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>, 
	Palmer Dabbelt <palmer@...belt.com>, Puranjay Mohan <puranjay12@...il.com>, 
	Rick Edgecombe <rick.p.edgecombe@...el.com>, Russell King <linux@...linux.org.uk>, 
	Steven Rostedt <rostedt@...dmis.org>, Thomas Bogendoerfer <tsbogend@...ha.franken.de>, 
	Thomas Gleixner <tglx@...utronix.de>, Will Deacon <will@...nel.org>, bpf@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-mips@...r.kernel.org, 
	linux-mm@...ck.org, linux-modules@...r.kernel.org, 
	linux-parisc@...r.kernel.org, linux-riscv@...ts.infradead.org, 
	linux-s390@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
	linuxppc-dev@...ts.ozlabs.org, loongarch@...ts.linux.dev, 
	netdev@...r.kernel.org, sparclinux@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v2 07/12] arm64, execmem: extend execmem_params for
 generated code definitions

On Sat, Jun 17, 2023 at 8:37 AM Kent Overstreet
<kent.overstreet@...ux.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 wonder
> > > 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 will
> > 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