Netdev Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Hao Luo <haoluo@google.com>
Cc: Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
	open list <linux-kernel@vger.kernel.org>,
	"open list:KERNEL SELFTEST FRAMEWORK" 
	<linux-kselftest@vger.kernel.org>, Shuah Khan <shuah@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Andrii Nakryiko <andriin@fb.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@chromium.org>,
	Quentin Monnet <quentin@isovalent.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ingo Molnar <mingo@redhat.com>, Andrey Ignatov <rdna@fb.com>,
	Jakub Sitnicki <jakub@cloudflare.com>
Subject: Re: [PATCH bpf-next v1 6/8] bpf: Introduce bpf_per_cpu_ptr()
Date: Sat, 22 Aug 2020 00:55:08 -0700	[thread overview]
Message-ID: <CAEf4BzZwtpvBSE=00XyHGr2p2OD6X_rwnntwvSZBjGvZUEZKCA@mail.gmail.com> (raw)
In-Reply-To: <CA+khW7jQmdw-TZMnST_rBcQWmxZ_eVw4ja+nsrqCM9HSkeWaXQ@mail.gmail.com>

On Sat, Aug 22, 2020 at 12:49 AM Hao Luo <haoluo@google.com> wrote:
>
> On Fri, Aug 21, 2020 at 8:31 PM Andrii Nakryiko
> <andrii.nakryiko@gmail.com> wrote:
> >
> > On Fri, Aug 21, 2020 at 8:26 PM Andrii Nakryiko
> > <andrii.nakryiko@gmail.com> wrote:
> > >
> > > On Wed, Aug 19, 2020 at 3:42 PM Hao Luo <haoluo@google.com> wrote:
> > > >
> > > > Add bpf_per_cpu_ptr() to help bpf programs access percpu vars.
> > > > bpf_per_cpu_ptr() has the same semantic as per_cpu_ptr() in the kernel
> > > > except that it may return NULL. This happens when the cpu parameter is
> > > > out of range. So the caller must check the returned value.
> > > >
> > > > Signed-off-by: Hao Luo <haoluo@google.com>
> > > > ---
> > >
> > > The logic looks correct, few naming nits, but otherwise:
> > >
> > > Acked-by: Andrii Nakryiko <andriin@fb.com>
> > >
> > > >  include/linux/bpf.h      |  3 ++
> > > >  include/linux/btf.h      | 11 +++++++
> > > >  include/uapi/linux/bpf.h | 14 +++++++++
> > > >  kernel/bpf/btf.c         | 10 -------
> > > >  kernel/bpf/verifier.c    | 64 ++++++++++++++++++++++++++++++++++++++--
> > > >  kernel/trace/bpf_trace.c | 18 +++++++++++
> > > >  6 files changed, 107 insertions(+), 13 deletions(-)
> [...]
> >
> > btw, having bpf_this_cpu_ptr(const void *ptr) seems worthwhile as well, WDYT?
> >
>
> It's probably not a good idea, IMHO. How does it interact with
> preemption? Should we treat it as __this_cpu_ptr()? If so, I feel it's
> easy to be misused, if the bpf program is called in a preemptible
> context.
>
> Btw, is bpf programs always called with preemption disabled? How about
> interrupts? I haven't thought about these questions before but I think
> they matter as we start to have more ways for bpf programs to interact
> with the kernel.

non-sleepable BPF is always disabling CPU migration, so there is no
problem with this_cpu_ptr. For sleepable not sure, but we can disable
this helper for sleepable BPF programs, if that's a problem.

>
> Best,
> Hao

  reply	other threads:[~2020-08-22  7:55 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-19 22:40 [PATCH bpf-next v1 0/8] bpf: BTF support for ksyms Hao Luo
2020-08-19 22:40 ` [PATCH bpf-next v1 1/8] bpf: Introduce pseudo_btf_id Hao Luo
2020-08-20 15:22   ` Yonghong Song
2020-08-20 17:04     ` Hao Luo
2020-08-25  0:05     ` Hao Luo
2020-08-25  0:43       ` Yonghong Song
2020-08-20 16:43   ` Yonghong Song
2020-08-20 21:53   ` Alexei Starovoitov
2020-08-21  2:22     ` Hao Luo
2020-08-19 22:40 ` [PATCH bpf-next v1 2/8] bpf: Propagate BPF_PSEUDO_BTF_ID to uapi headers in /tools Hao Luo
2020-08-20 16:44   ` Yonghong Song
2020-08-19 22:40 ` [PATCH bpf-next v1 3/8] bpf: Introduce help function to validate ksym's type Hao Luo
2020-08-20 17:20   ` Yonghong Song
2020-08-21 21:50     ` Andrii Nakryiko
2020-08-22  0:43       ` Hao Luo
2020-08-22  2:43         ` Andrii Nakryiko
2020-08-22  7:04           ` Hao Luo
2020-08-19 22:40 ` [PATCH bpf-next v1 4/8] bpf/libbpf: BTF support for typed ksyms Hao Luo
2020-08-21 22:37   ` Andrii Nakryiko
2020-08-27 22:29     ` Hao Luo
2020-09-01 18:11       ` Andrii Nakryiko
2020-09-01 20:35         ` Hao Luo
2020-09-01 23:54           ` Andrii Nakryiko
2020-09-02  0:46             ` Hao Luo
2020-08-19 22:40 ` [PATCH bpf-next v1 5/8] bpf/selftests: ksyms_btf to test " Hao Luo
2020-08-20 17:28   ` Yonghong Song
2020-08-21 23:03     ` Andrii Nakryiko
2020-08-22  7:26       ` Hao Luo
2020-08-22  7:35         ` Andrii Nakryiko
2020-08-19 22:40 ` [PATCH bpf-next v1 6/8] bpf: Introduce bpf_per_cpu_ptr() Hao Luo
2020-08-22  3:26   ` Andrii Nakryiko
2020-08-22  3:31     ` Andrii Nakryiko
2020-08-22  7:49       ` Hao Luo
2020-08-22  7:55         ` Andrii Nakryiko [this message]
2020-08-25  1:03           ` Hao Luo
2020-08-19 22:40 ` [PATCH bpf-next v1 7/8] bpf: Propagate bpf_per_cpu_ptr() to /tools Hao Luo
2020-08-20 17:30   ` Yonghong Song
2020-08-19 22:40 ` [PATCH bpf-next v1 8/8] bpf/selftests: Test for bpf_per_cpu_ptr() Hao Luo
2020-08-22  3:30   ` Andrii Nakryiko
2020-08-28  3:42     ` Hao Luo
2020-09-01 18:12       ` Andrii Nakryiko
2020-09-01 19:47         ` Hao Luo

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='CAEf4BzZwtpvBSE=00XyHGr2p2OD6X_rwnntwvSZBjGvZUEZKCA@mail.gmail.com' \
    --to=andrii.nakryiko@gmail.com \
    --cc=andriin@fb.com \
    --cc=ast@kernel.org \
    --cc=bpf@vger.kernel.org \
    --cc=daniel@iogearbox.net \
    --cc=haoluo@google.com \
    --cc=jakub@cloudflare.com \
    --cc=john.fastabend@gmail.com \
    --cc=kafai@fb.com \
    --cc=kpsingh@chromium.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-kselftest@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=netdev@vger.kernel.org \
    --cc=quentin@isovalent.com \
    --cc=rdna@fb.com \
    --cc=rostedt@goodmis.org \
    --cc=shuah@kernel.org \
    --cc=songliubraving@fb.com \
    --cc=yhs@fb.com \
    --subject='Re: [PATCH bpf-next v1 6/8] bpf: Introduce bpf_per_cpu_ptr()' \
    /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

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).