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From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Alexei Starovoitov <ast@kernel.org>
Cc: "David S. Miller" <davem@davemloft.net>,
	Daniel Borkmann <daniel@iogearbox.net>,
	x86@kernel.org, Networking <netdev@vger.kernel.org>,
	bpf <bpf@vger.kernel.org>, Kernel Team <kernel-team@fb.com>
Subject: Re: [PATCH v3 bpf-next 09/11] bpf: add support for BTF pointers to x86 JIT
Date: Wed, 16 Oct 2019 13:15:23 -0700	[thread overview]
Message-ID: <CAEf4BzZ+p718RBxQUO5hDv3bfXz=KPcuxmLhHw3P9hHKSp4MCA@mail.gmail.com> (raw)
In-Reply-To: <20191016032505.2089704-10-ast@kernel.org>

On Wed, Oct 16, 2019 at 4:16 AM Alexei Starovoitov <ast@kernel.org> wrote:
>
> Pointer to BTF object is a pointer to kernel object or NULL.
> Such pointers can only be used by BPF_LDX instructions.
> The verifier changed their opcode from LDX|MEM|size
> to LDX|PROBE_MEM|size to make JITing easier.
> The number of entries in extable is the number of BPF_LDX insns
> that access kernel memory via "pointer to BTF type".
> Only these load instructions can fault.
> Since x86 extable is relative it has to be allocated in the same
> memory region as JITed code.
> Allocate it prior to last pass of JITing and let the last pass populate it.
> Pointer to extable in bpf_prog_aux is necessary to make page fault
> handling fast.
> Page fault handling is done in two steps:
> 1. bpf_prog_kallsyms_find() finds BPF program that page faulted.
>    It's done by walking rb tree.
> 2. then extable for given bpf program is binary searched.
> This process is similar to how page faulting is done for kernel modules.
> The exception handler skips over faulting x86 instruction and
> initializes destination register with zero. This mimics exact
> behavior of bpf_probe_read (when probe_kernel_read faults dest is zeroed).
>
> JITs for other architectures can add support in similar way.
> Until then they will reject unknown opcode and fallback to interpreter.
>
> Since extable should be aligned and placed near JITed code
> make bpf_jit_binary_alloc() return 4 byte aligned image offset,
> so that extable aligning formula in bpf_int_jit_compile() doesn't need
> to rely on internal implementation of bpf_jit_binary_alloc().
> On x86 gcc defaults to 16-byte alignment for regular kernel functions
> due to better performance. JITed code may be aligned to 16 in the future,
> but it will use 4 in the meantime.
>
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> ---

Missed my ack from v2:

Acked-by: Andrii Nakryiko <andriin@fb.com>

>  arch/x86/net/bpf_jit_comp.c | 97 +++++++++++++++++++++++++++++++++++--
>  include/linux/bpf.h         |  3 ++
>  include/linux/extable.h     | 10 ++++
>  kernel/bpf/core.c           | 20 +++++++-
>  kernel/bpf/verifier.c       |  1 +
>  kernel/extable.c            |  2 +
>  6 files changed, 128 insertions(+), 5 deletions(-)
>

[...]

  reply	other threads:[~2019-10-16 20:15 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-16  3:24 [PATCH v3 bpf-next 00/11] bpf: revolutionize bpf tracing Alexei Starovoitov
2019-10-16  3:24 ` [PATCH v3 bpf-next 01/11] bpf: add typecast to raw_tracepoints to help BTF generation Alexei Starovoitov
2019-10-16  3:24 ` [PATCH v3 bpf-next 02/11] bpf: add typecast to bpf helpers " Alexei Starovoitov
2019-10-16  3:24 ` [PATCH v3 bpf-next 03/11] bpf: process in-kernel BTF Alexei Starovoitov
2019-10-16  3:24 ` [PATCH v3 bpf-next 04/11] bpf: add attach_btf_id attribute to program load Alexei Starovoitov
2019-10-16 19:45   ` Andrii Nakryiko
2019-10-16 19:50     ` Alexei Starovoitov
2019-10-16  3:24 ` [PATCH v3 bpf-next 05/11] libbpf: auto-detect btf_id of BTF-based raw_tracepoints Alexei Starovoitov
2019-10-16 19:49   ` Andrii Nakryiko
2019-10-16  3:25 ` [PATCH v3 bpf-next 06/11] bpf: implement accurate raw_tp context access via BTF Alexei Starovoitov
2019-10-16 20:09   ` Andrii Nakryiko
2019-10-16 21:21   ` Daniel Borkmann
2019-10-16 21:28     ` Alexei Starovoitov
2019-10-16 22:08       ` Daniel Borkmann
2019-10-16 23:52         ` Alexei Starovoitov
2019-10-16  3:25 ` [PATCH v3 bpf-next 07/11] bpf: attach raw_tp program with BTF via type name Alexei Starovoitov
2019-10-16 20:13   ` Andrii Nakryiko
2019-10-16  3:25 ` [PATCH v3 bpf-next 08/11] bpf: add support for BTF pointers to interpreter Alexei Starovoitov
2019-10-16  3:25 ` [PATCH v3 bpf-next 09/11] bpf: add support for BTF pointers to x86 JIT Alexei Starovoitov
2019-10-16 20:15   ` Andrii Nakryiko [this message]
2019-10-16  3:25 ` [PATCH v3 bpf-next 10/11] bpf: check types of arguments passed into helpers Alexei Starovoitov
2019-10-16  3:25 ` [PATCH v3 bpf-next 11/11] selftests/bpf: add kfree_skb raw_tp test Alexei Starovoitov
2019-10-16 18:01 ` [PATCH v3 bpf-next 00/11] bpf: revolutionize bpf tracing Martin Lau
2019-10-17 15:14 ` Daniel Borkmann

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