From: Song Liu <songliubraving@fb.com>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Ilya Leoshkevich <iii@linux.ibm.com>, Song Liu <song@kernel.org>,
bpf <bpf@vger.kernel.org>,
Network Development <netdev@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
"Kernel Team" <Kernel-team@fb.com>,
Peter Zijlstra <peterz@infradead.org>, X86 ML <x86@kernel.org>
Subject: Re: [PATCH v6 bpf-next 6/7] bpf: introduce bpf_prog_pack allocator
Date: Sun, 23 Jan 2022 01:03:25 +0000 [thread overview]
Message-ID: <5E70BF53-E3FB-4F7A-B55D-199C54A8FDCA@fb.com> (raw)
In-Reply-To: <CAADnVQLXGu_eF8VT6NmxKVxOHmfx7C=mWmmWF8KmsjFXg6P5OA@mail.gmail.com>
> On Jan 21, 2022, at 6:12 PM, Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:
>
> On Fri, Jan 21, 2022 at 5:30 PM Song Liu <songliubraving@fb.com> wrote:
>>
>>
>>
>>> On Jan 21, 2022, at 5:12 PM, Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:
>>>
>>> On Fri, Jan 21, 2022 at 5:01 PM Song Liu <songliubraving@fb.com> wrote:
>>>>
>>>> In this way, we need to allocate rw_image here, and free it in
>>>> bpf_jit_comp.c. This feels a little weird to me, but I guess that
>>>> is still the cleanest solution for now.
>>>
>>> You mean inside bpf_jit_binary_alloc?
>>> That won't be arch independent.
>>> It needs to be split into generic piece that stays in core.c
>>> and callbacks like bpf_jit_fill_hole_t
>>> or into multiple helpers with prep in-between.
>>> Don't worry if all archs need to be touched.
>>
>> How about we introduce callback bpf_jit_set_header_size_t? Then we
>> can split x86's jit_fill_hole() into two functions, one to fill the
>> hole, the other to set size. The rest of the logic gonna stay the same.
>>
>> Archs that do not use bpf_prog_pack won't need bpf_jit_set_header_size_t.
>
> That's not any better.
>
> Currently the choice of bpf_jit_binary_alloc_pack vs bpf_jit_binary_alloc
> leaks into arch bits and bpf_prog_pack_max_size() doesn't
> really make it generic.
>
> Ideally all archs continue to use bpf_jit_binary_alloc()
> and magic happens in a generic code.
> If not then please remove bpf_prog_pack_max_size(),
> since it doesn't provide much value and pick
> bpf_jit_binary_alloc_pack() signature to fit x86 jit better.
> It wouldn't need bpf_jit_fill_hole_t callback at all.
> Please think it through so we don't need to redesign it
> when another arch will decide to use huge pages for bpf progs.
>
> cc-ing Ilya for ideas on how that would fit s390.
I guess we have a few different questions here:
1. Can we use bpf_jit_binary_alloc() for both regular page and shared
huge page?
I think the answer is no, as bpf_jit_binary_alloc() allocates a rw
buffer, and arch calls bpf_jit_binary_lock_ro after JITing. The new
allocator will return a slice of a shared huge page, which is locked
RO before JITing.
2. The problem with bpf_prog_pack_max_size() limitation.
I think this is the worst part of current version of bpf_prog_pack,
but it shouldn't be too hard to fix. I will remove this limitation
in the next version.
3. How to set proper header->size?
I guess we can introduce something similar to bpf_arch_text_poke()
for this?
My proposal for the next version is:
1. No changes to archs that do not use huge page, just keep using
bpf_jit_binary_alloc.
2. For x86_64 (and other arch that would support bpf program on huge
pages):
2.1 arch/bpf_jit_comp calls bpf_jit_binary_alloc_pack() to allocate
an RO bpf_binary_header;
2.2 arch allocates a temporary buffer for JIT. Once JIT is done,
use text_poke_copy to copy the code to the RO bpf_binary_header.
3. Remove bpf_prog_pack_max_size limitation.
Does this sound reasonable?
Thanks,
Song
next prev parent reply other threads:[~2022-01-23 1:03 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-21 19:49 [PATCH v6 bpf-next 0/7] bpf_prog_pack allocator Song Liu
2022-01-21 19:49 ` [PATCH v6 bpf-next 1/7] x86/Kconfig: select HAVE_ARCH_HUGE_VMALLOC with HAVE_ARCH_HUGE_VMAP Song Liu
2022-01-21 19:49 ` [PATCH v6 bpf-next 2/7] bpf: use bytes instead of pages for bpf_jit_[charge|uncharge]_modmem Song Liu
2022-01-21 19:49 ` [PATCH v6 bpf-next 3/7] bpf: use size instead of pages in bpf_binary_header Song Liu
2022-01-21 19:49 ` [PATCH v6 bpf-next 4/7] bpf: add a pointer of bpf_binary_header to bpf_prog Song Liu
2022-01-21 19:49 ` [PATCH v6 bpf-next 5/7] x86/alternative: introduce text_poke_copy Song Liu
2022-01-21 19:49 ` [PATCH v6 bpf-next 6/7] bpf: introduce bpf_prog_pack allocator Song Liu
2022-01-21 23:55 ` Alexei Starovoitov
2022-01-22 0:23 ` Song Liu
2022-01-22 0:41 ` Alexei Starovoitov
2022-01-22 1:01 ` Song Liu
2022-01-22 1:12 ` Alexei Starovoitov
2022-01-22 1:30 ` Song Liu
2022-01-22 2:12 ` Alexei Starovoitov
2022-01-23 1:03 ` Song Liu [this message]
2022-01-24 12:29 ` Ilya Leoshkevich
2022-01-24 18:27 ` Song Liu
2022-01-25 5:21 ` Alexei Starovoitov
2022-01-25 7:21 ` Song Liu
2022-01-25 19:59 ` Alexei Starovoitov
2022-01-25 22:25 ` Song Liu
2022-01-25 22:48 ` Alexei Starovoitov
2022-01-25 23:09 ` Song Liu
2022-01-26 0:38 ` Alexei Starovoitov
2022-01-26 0:50 ` Song Liu
2022-01-26 1:20 ` Alexei Starovoitov
2022-01-26 1:28 ` Song Liu
2022-01-26 1:31 ` Song Liu
2022-01-26 1:34 ` Alexei Starovoitov
2022-01-24 12:45 ` Peter Zijlstra
2022-01-21 19:49 ` [PATCH v6 bpf-next 7/7] bpf, x86_64: use " Song Liu
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