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

From: Kent Overstreet <kent.overstreet@linux.dev>
To: Mike Rapoport <rppt@kernel.org>
Cc: Song Liu <song@kernel.org>, Mark Rutland <mark.rutland@arm.com>,
	linux-kernel@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Christophe Leroy <christophe.leroy@csgroup.eu>,
	"David S. Miller" <davem@davemloft.net>,
	Dinh Nguyen <dinguyen@kernel.org>,
	Heiko Carstens <hca@linux.ibm.com>, Helge Deller <deller@gmx.de>,
	Huacai Chen <chenhuacai@kernel.org>,
	Luis Chamberlain <mcgrof@kernel.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	"Naveen N. Rao" <naveen.n.rao@linux.ibm.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Russell King <linux@armlinux.org.uk>,
	Steven Rostedt <rostedt@goodmis.org>,
	Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Will Deacon <will@kernel.org>,
	bpf@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-mips@vger.kernel.org, linux-mm@kvack.org,
	linux-modules@vger.kernel.org, linux-parisc@vger.kernel.org,
	linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org,
	linux-trace-kernel@vger.kernel.org,
	linuxppc-dev@lists.ozlabs.org, loongarch@lists.linux.dev,
	netdev@vger.kernel.org, sparclinux@vger.kernel.org,
	x86@kernel.org
Subject: Re: [PATCH 00/13] mm: jit/text allocator
Date: Tue, 13 Jun 2023 14:56:14 -0400	[thread overview]
Message-ID: <ZIi7zmey0w61EG25@moria.home.lan> (raw)
In-Reply-To: <20230608184116.GJ52412@kernel.org>

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@arm.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.

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