netdev - Re: [PATCH 00/13] mm: jit/text allocator

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Date: Wed, 14 Jun 2023 00:09:00 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Kent Overstreet <kent.overstreet@...ux.dev>
Cc: Song Liu <song@...nel.org>, Mark Rutland <mark.rutland@....com>,
	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>,
	Michael Ellerman <mpe@...erman.id.au>,
	"Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
	Palmer Dabbelt <palmer@...belt.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 00/13] mm: jit/text allocator

On Tue, Jun 13, 2023 at 02:56:14PM -0400, Kent Overstreet wrote:
> On Thu, Jun 08, 2023 at 09:41:16PM +0300, Mike Rapoport wrote:
> > On Tue, Jun 06, 2023 at 11:21:59AM -0700, Song Liu wrote:
> > > On Mon, Jun 5, 2023 at 3:09 AM Mark Rutland <mark.rutland@....com> wrote:
> > > 
> > > [...]
> > > 
> > > > > > > Can you give more detail on what parameters you need? If the only extra
> > > > > > > parameter is just "does this allocation need to live close to kernel
> > > > > > > text", that's not that big of a deal.
> > > > > >
> > > > > > My thinking was that we at least need the start + end for each caller. That
> > > > > > might be it, tbh.
> > > > >
> > > > > Do you mean that modules will have something like
> > > > >
> > > > >       jit_text_alloc(size, MODULES_START, MODULES_END);
> > > > >
> > > > > and kprobes will have
> > > > >
> > > > >       jit_text_alloc(size, KPROBES_START, KPROBES_END);
> > > > > ?
> > > >
> > > > Yes.
> > > 
> > > How about we start with two APIs:
> > >      jit_text_alloc(size);
> > >      jit_text_alloc_range(size, start, end);
> > > 
> > > AFAICT, arm64 is the only arch that requires the latter API. And TBH, I am
> > > not quite convinced it is needed.
> >  
> > Right now arm64 and riscv override bpf and kprobes allocations to use the
> > entire vmalloc address space, but having the ability to allocate generated
> > code outside of modules area may be useful for other architectures.
> > 
> > Still the start + end for the callers feels backwards to me because the
> > callers do not define the ranges, but rather the architectures, so we still
> > need a way for architectures to define how they want allocate memory for
> > the generated code.
> 
> So, the start + end just comes from the need to keep relative pointers
> under a certain size. I think this could be just a flag, I see no reason
> to expose actual addresses here.

It's the other way around. The start + end comes from the need to restrict
allocation to certain range because of the relative addressing. I don't see
how a flag can help here.

-- 
Sincerely yours,
Mike.