linux-kernel - Re: [PATCH v2 02/12] mm: introduce execmem_text_alloc() and jit_text

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Date:   Fri, 16 Jun 2023 11:18:41 -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 02/12] mm: introduce execmem_text_alloc() and jit_text_alloc()

On Fri, Jun 16, 2023 at 9:48 AM Kent Overstreet
<kent.overstreet@...ux.dev> wrote:
>
> On Fri, Jun 16, 2023 at 11:50:28AM +0300, Mike Rapoport wrote:
> > From: "Mike Rapoport (IBM)" <rppt@...nel.org>
> >
> > module_alloc() is used everywhere as a mean to allocate memory for code.
> >
> > Beside being semantically wrong, this unnecessarily ties all subsystems
> > that need to allocate code, such as ftrace, kprobes and BPF to modules
> > and puts the burden of code allocation to the modules code.
> >
> > Several architectures override module_alloc() because of various
> > constraints where the executable memory can be located and this causes
> > additional obstacles for improvements of code allocation.
> >
> > Start splitting code allocation from modules by introducing
> > execmem_text_alloc(), execmem_free(), jit_text_alloc(), jit_free() APIs.
> >
> > Initially, execmem_text_alloc() and jit_text_alloc() are wrappers for
> > module_alloc() and execmem_free() and jit_free() are replacements of
> > module_memfree() to allow updating all call sites to use the new APIs.
> >
> > The intention semantics for new allocation APIs:
> >
> > * execmem_text_alloc() should be used to allocate memory that must reside
> >   close to the kernel image, like loadable kernel modules and generated
> >   code that is restricted by relative addressing.
> >
> > * jit_text_alloc() should be used to allocate memory for generated code
> >   when there are no restrictions for the code placement. For
> >   architectures that require that any code is within certain distance
> >   from the kernel image, jit_text_alloc() will be essentially aliased to
> >   execmem_text_alloc().
> >
> > The names execmem_text_alloc() and jit_text_alloc() emphasize that the
> > allocated memory is for executable code, the allocations of the
> > associated data, like data sections of a module will use
> > execmem_data_alloc() interface that will be added later.
>
> I like the API split - at the risk of further bikeshedding, perhaps
> near_text_alloc() and far_text_alloc()? Would be more explicit.
>
> Reviewed-by: Kent Overstreet <kent.overstreet@...ux.dev>

Acked-by: Song Liu <song@...nel.org>