All of lore.kernel.org
 help / color / mirror / Atom feed
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 v2 bpf-next 09/12] bpf: add support for BTF pointers to x86 JIT
Date: Fri, 11 Oct 2019 11:48:19 -0700	[thread overview]
Message-ID: <CAEf4BzZ3A47KQB1uN0nu2JPdm-a+Kx0fkkkp+JRRLNs4DJJ3hw@mail.gmail.com> (raw)
In-Reply-To: <20191010041503.2526303-10-ast@kernel.org>

On Wed, Oct 9, 2019 at 9:15 PM 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>
> ---

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:[~2019-10-11 18:48 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-10  4:14 [PATCH v2 bpf-next 00/12] bpf: revolutionize bpf tracing Alexei Starovoitov
2019-10-10  4:14 ` [PATCH v2 bpf-next 01/12] bpf: add typecast to raw_tracepoints to help BTF generation Alexei Starovoitov
2019-10-10  4:14 ` [PATCH v2 bpf-next 02/12] bpf: add typecast to bpf helpers " Alexei Starovoitov
2019-10-10  4:14 ` [PATCH v2 bpf-next 03/12] bpf: process in-kernel BTF Alexei Starovoitov
2019-10-11 17:56   ` Andrii Nakryiko
2019-10-10  4:14 ` [PATCH v2 bpf-next 04/12] bpf: add attach_btf_id attribute to program load Alexei Starovoitov
2019-10-11 17:58   ` Andrii Nakryiko
2019-10-10  4:14 ` [PATCH v2 bpf-next 05/12] libbpf: auto-detect btf_id of raw_tracepoint Alexei Starovoitov
2019-10-11 18:02   ` Andrii Nakryiko
2019-10-11 18:07   ` Andrii Nakryiko
2019-10-12  0:40     ` Alexei Starovoitov
2019-10-12  1:29       ` Alexei Starovoitov
2019-10-12  4:38         ` Andrii Nakryiko
2019-10-12  4:53           ` Alexei Starovoitov
2019-10-12  4:39       ` Andrii Nakryiko
2019-10-10  4:14 ` [PATCH v2 bpf-next 06/12] bpf: implement accurate raw_tp context access via BTF Alexei Starovoitov
2019-10-11 18:31   ` Andrii Nakryiko
2019-10-11 23:13     ` Andrii Nakryiko
2019-10-10  4:14 ` [PATCH v2 bpf-next 07/12] bpf: attach raw_tp program with BTF via type name Alexei Starovoitov
2019-10-11 18:44   ` Andrii Nakryiko
2019-10-10  4:14 ` [PATCH v2 bpf-next 08/12] bpf: add support for BTF pointers to interpreter Alexei Starovoitov
2019-10-10  4:15 ` [PATCH v2 bpf-next 09/12] bpf: add support for BTF pointers to x86 JIT Alexei Starovoitov
2019-10-11 18:48   ` Andrii Nakryiko [this message]
2019-10-10  4:15 ` [PATCH v2 bpf-next 10/12] bpf: check types of arguments passed into helpers Alexei Starovoitov
2019-10-11 19:02   ` Andrii Nakryiko
2019-10-12  1:39     ` Alexei Starovoitov
2019-10-12  4:25       ` Andrii Nakryiko
2019-10-10  4:15 ` [PATCH v2 bpf-next 11/12] bpf: disallow bpf_probe_read[_str] helpers Alexei Starovoitov
2019-10-11 19:03   ` Andrii Nakryiko
2019-10-10  4:15 ` [PATCH v2 bpf-next 12/12] selftests/bpf: add kfree_skb raw_tp test Alexei Starovoitov
2019-10-10 11:07   ` Ido Schimmel
2019-10-10 19:07     ` Alexei Starovoitov
2019-10-11 19:05   ` Andrii Nakryiko

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=CAEf4BzZ3A47KQB1uN0nu2JPdm-a+Kx0fkkkp+JRRLNs4DJJ3hw@mail.gmail.com \
    --to=andrii.nakryiko@gmail.com \
    --cc=ast@kernel.org \
    --cc=bpf@vger.kernel.org \
    --cc=daniel@iogearbox.net \
    --cc=davem@davemloft.net \
    --cc=kernel-team@fb.com \
    --cc=netdev@vger.kernel.org \
    --cc=x86@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.