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Date:   Tue, 13 Jun 2023 14:56:14 -0400
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>,
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Subject: Re: [PATCH 00/13] mm: jit/text allocator
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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.