From: Mike Rapoport <rppt@kernel.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
linux-kernel@vger.kernel.org,
Alexandre Ghiti <alexghiti@rivosinc.com>,
Andrew Morton <akpm@linux-foundation.org>,
"Bj\"orn T\"opel" <bjorn@kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Christophe Leroy <christophe.leroy@csgroup.eu>,
"David S. Miller" <davem@davemloft.net>,
Dinh Nguyen <dinguyen@kernel.org>,
Donald Dutile <ddutile@redhat.com>,
Eric Chanudet <echanude@redhat.com>,
Heiko Carstens <hca@linux.ibm.com>, Helge Deller <deller@gmx.de>,
Huacai Chen <chenhuacai@kernel.org>,
Kent Overstreet <kent.overstreet@linux.dev>,
Luis Chamberlain <mcgrof@kernel.org>,
Michael Ellerman <mpe@ellerman.id.au>,
Nadav Amit <nadav.amit@gmail.com>,
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Puranjay Mohan <puranjay12@gmail.com>,
Rick Edgecombe <rick.p.edgecombe@intel.com>,
Russell King <linux@armlinux.org.uk>, Song Liu <song@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
Thomas Gleixner <tglx@linutronix.de>,
Will Deacon <will@kernel.org>,
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linuxppc-dev@lists.ozlabs.org, loongarch@lists.linux.dev,
netdev@vger.kernel.org, sparclinux@vger.kernel.org,
x86@kernel.org
Subject: Re: [PATCH v4 05/15] mm: introduce execmem_alloc() and execmem_free()
Date: Tue, 16 Apr 2024 10:22:14 +0300 [thread overview]
Message-ID: <Zh4nJp8rv1qRBs8m@kernel.org> (raw)
In-Reply-To: <Zh1lnIdgFeM1o8S5@FVFF77S0Q05N.cambridge.arm.com>
On Mon, Apr 15, 2024 at 06:36:39PM +0100, Mark Rutland wrote:
> On Mon, Apr 15, 2024 at 09:52:41AM +0200, Peter Zijlstra wrote:
> > On Thu, Apr 11, 2024 at 07:00:41PM +0300, Mike Rapoport wrote:
> > > +/**
> > > + * enum execmem_type - types of executable memory ranges
> > > + *
> > > + * There are several subsystems that allocate executable memory.
> > > + * Architectures define different restrictions on placement,
> > > + * permissions, alignment and other parameters for memory that can be used
> > > + * by these subsystems.
> > > + * Types in this enum identify subsystems that allocate executable memory
> > > + * and let architectures define parameters for ranges suitable for
> > > + * allocations by each subsystem.
> > > + *
> > > + * @EXECMEM_DEFAULT: default parameters that would be used for types that
> > > + * are not explcitly defined.
> > > + * @EXECMEM_MODULE_TEXT: parameters for module text sections
> > > + * @EXECMEM_KPROBES: parameters for kprobes
> > > + * @EXECMEM_FTRACE: parameters for ftrace
> > > + * @EXECMEM_BPF: parameters for BPF
> > > + * @EXECMEM_TYPE_MAX:
> > > + */
> > > +enum execmem_type {
> > > + EXECMEM_DEFAULT,
> > > + EXECMEM_MODULE_TEXT = EXECMEM_DEFAULT,
> > > + EXECMEM_KPROBES,
> > > + EXECMEM_FTRACE,
> > > + EXECMEM_BPF,
> > > + EXECMEM_TYPE_MAX,
> > > +};
> >
> > Can we please get a break-down of how all these types are actually
> > different from one another?
> >
> > I'm thinking some platforms have a tiny immediate space (arm64 comes to
> > mind) and has less strict placement constraints for some of them?
>
> Yeah, and really I'd *much* rather deal with that in arch code, as I have said
> several times.
>
> For arm64 we have two bsaic restrictions:
>
> 1) Direct branches can go +/-128M
> We can expand this range by having direct branches go to PLTs, at a
> performance cost.
>
> 2) PREL32 relocations can go +/-2G
> We cannot expand this further.
>
> * We don't need to allocate memory for ftrace. We do not use trampolines.
>
> * Kprobes XOL areas don't care about either of those; we don't place any
> PC-relative instructions in those. Maybe we want to in future.
>
> * Modules care about both; we'd *prefer* to place them within +/-128M of all
> other kernel/module code, but if there's no space we can use PLTs and expand
> that to +/-2G. Since modules can refreence other modules, that ends up
> actually being halved, and modules have to fit within some 2G window that
> also covers the kernel.
>
> * I'm not sure about BPF's requirements; it seems happy doing the same as
> modules.
BPF are happy with vmalloc().
> So if we *must* use a common execmem allocator, what we'd reall want is our own
> types, e.g.
>
> EXECMEM_ANYWHERE
> EXECMEM_NOPLT
> EXECMEM_PREL32
>
> ... and then we use those in arch code to implement module_alloc() and friends.
I'm looking at execmem_types more as definition of the consumers, maybe I
should have named the enum execmem_consumer at the first place.
And the arch constrains defined in struct execmem_range describe how memory
should be allocated for each consumer.
These constraints are defined early at boot and remain static, so
initializing them once and letting a common allocator use them makes
perfect sense to me.
I agree that fallback_{start,end} are not ideal, but we have 3
architectures that have preferred and secondary range for modules. And arm
and powerpc use the same logic for kprobes as well, and I don't see why this
code should be duplicated.
And, for instance, if you decide to place PC-relative instructions if
kprobes XOL areas, you'd only need to update execmem_range for kprobes to
be more like the range for modules.
With central allocator it's easier to deal with the things like
VM_FLUSH_RESET_PERMS and caching of ROX memory and I think it will be more
maintainable that module_alloc(), alloc_insn_page() and
bpf_jit_alloc_exec() spread all over the place.
> Mark.
--
Sincerely yours,
Mike.
next prev parent reply other threads:[~2024-04-16 7:23 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-11 16:00 [PATCH v4 00/15] mm: jit/text allocator Mike Rapoport
2024-04-11 16:00 ` [PATCH v4 01/15] arm64: module: remove uneeded call to kasan_alloc_module_shadow() Mike Rapoport
2024-04-11 16:00 ` [PATCH v4 02/15] mips: module: rename MODULE_START to MODULES_VADDR Mike Rapoport
2024-04-11 16:00 ` [PATCH v4 03/15] nios2: define virtual address space for modules Mike Rapoport
2024-04-11 16:00 ` [PATCH v4 04/15] module: make module_memory_{alloc,free} more self-contained Mike Rapoport
2024-04-11 16:00 ` [PATCH v4 05/15] mm: introduce execmem_alloc() and execmem_free() Mike Rapoport
2024-04-11 19:42 ` Luis Chamberlain
2024-04-14 6:53 ` Mike Rapoport
2024-04-12 9:16 ` Ingo Molnar
2024-04-14 6:54 ` Mike Rapoport
2024-04-15 7:52 ` Peter Zijlstra
2024-04-15 16:51 ` Mike Rapoport
2024-04-15 17:36 ` Mark Rutland
2024-04-16 7:22 ` Mike Rapoport [this message]
2024-04-17 23:32 ` Song Liu
2024-04-18 15:35 ` Mike Rapoport
2024-04-18 16:13 ` Song Liu
2024-04-18 17:52 ` Mike Rapoport
2024-04-18 21:01 ` Song Liu
2024-04-19 6:55 ` Mike Rapoport
2024-04-19 15:54 ` Song Liu
2024-04-19 17:02 ` Mike Rapoport
2024-04-19 17:32 ` Song Liu
2024-04-19 19:59 ` Mike Rapoport
2024-04-19 21:42 ` Song Liu
2024-04-20 4:22 ` Mike Rapoport
2024-04-20 9:11 ` Masami Hiramatsu
2024-04-22 18:32 ` Song Liu
2024-04-17 21:06 ` Masami Hiramatsu
2024-04-11 16:00 ` [PATCH v4 06/15] mm/execmem, arch: convert simple overrides of module_alloc to execmem Mike Rapoport
2024-04-11 20:53 ` Sam Ravnborg
2024-04-14 7:26 ` Mike Rapoport
2024-04-15 8:03 ` Peter Zijlstra
2024-04-11 16:00 ` [PATCH v4 07/15] mm/execmem, arch: convert remaining " Mike Rapoport
2024-04-15 9:36 ` Peter Zijlstra
2024-04-11 16:00 ` [PATCH v4 08/15] arm64: extend execmem_info for generated code allocations Mike Rapoport
2024-04-11 16:00 ` [PATCH v4 09/15] riscv: extend execmem_params " Mike Rapoport
2024-04-11 16:00 ` [PATCH v4 10/15] powerpc: extend execmem_params for kprobes allocations Mike Rapoport
2024-04-11 16:00 ` [PATCH v4 11/15] arch: make execmem setup available regardless of CONFIG_MODULES Mike Rapoport
2024-04-11 16:00 ` [PATCH v4 12/15] x86/ftrace: enable dynamic ftrace without CONFIG_MODULES Mike Rapoport
2024-04-11 16:00 ` [PATCH v4 13/15] powerpc: use CONFIG_EXECMEM instead of CONFIG_MODULES where appropiate Mike Rapoport
2024-04-11 16:00 ` [PATCH v4 14/15] kprobes: remove dependency on CONFIG_MODULES Mike Rapoport
2024-04-17 21:16 ` Masami Hiramatsu
2024-04-18 15:37 ` Mike Rapoport
2024-04-19 15:49 ` Mike Rapoport
2024-04-19 15:59 ` Christophe Leroy
2024-04-20 7:33 ` Mike Rapoport
2024-04-20 9:15 ` Masami Hiramatsu
2024-04-20 10:52 ` Mike Rapoport
2024-04-11 16:00 ` [PATCH v4 15/15] bpf: remove CONFIG_BPF_JIT dependency on CONFIG_MODULES of Mike Rapoport
2024-04-11 18:00 ` [PATCH v4 00/15] mm: jit/text allocator Kent Overstreet
2024-04-11 19:45 ` Luis Chamberlain
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