From: David Vernet <void@manifault.com>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net,
andrii@kernel.org, john.fastabend@gmail.com,
martin.lau@linux.dev, song@kernel.org, yhs@fb.com,
kpsingh@kernel.org, sdf@google.com, haoluo@google.com,
jolsa@kernel.org, tj@kernel.org, joannelkoong@gmail.com,
linux-kernel@vger.kernel.org, Kernel-team@fb.com
Subject: Re: [PATCH 2/5] bpf: Define new BPF_MAP_TYPE_USER_RINGBUF map type
Date: Fri, 12 Aug 2022 11:23:24 -0500 [thread overview]
Message-ID: <YvZ+fHcKUnUk8jhc@maniforge.dhcp.thefacebook.com> (raw)
In-Reply-To: <CAEf4BzZdOQwym4Q2QXtWF9uKhtKEb8cya-eQvLU3h3+7wES8UA@mail.gmail.com>
On Thu, Aug 11, 2022 at 04:29:02PM -0700, Andrii Nakryiko wrote:
[...]
> > - /* Consumer and producer counters are put into separate pages to allow
> > - * mapping consumer page as r/w, but restrict producer page to r/o.
> > - * This protects producer position from being modified by user-space
> > - * application and ruining in-kernel position tracking.
> > + /* Consumer and producer counters are put into separate pages to
> > + * allow each position to be mapped with different permissions.
> > + * This prevents a user-space application from modifying the
> > + * position and ruining in-kernel tracking. The permissions of the
> > + * pages depend on who is producing samples: user-space or the
> > + * kernel.
> > + *
> > + * Kernel-producer
> > + * ---------------
> > + * The producer position and data pages are mapped as r/o in
> > + * userspace. For this approach, bits in the header of samples are
> > + * used to signal to user-space, and to other producers, whether a
> > + * sample is currently being written.
> > + *
> > + * User-space producer
> > + * -------------------
> > + * Only the page containing the consumer position, and whether the
> > + * ringbuffer is currently being consumed via a 'busy' bit, are
> > + * mapped r/o in user-space. Sample headers may not be used to
> > + * communicate any information between kernel consumers, as a
> > + * user-space application could modify its contents at any time.
> > */
> > - unsigned long consumer_pos __aligned(PAGE_SIZE);
> > + struct {
> > + unsigned long consumer_pos;
> > + atomic_t busy;
>
> one more thing, why does busy have to be exposed into user-space
> mapped memory at all? Can't it be just a private variable in
> bpf_ringbuf?
It could be moved elsewhere in the struct. I put it here to avoid
increasing the size of struct bpf_ringbuf unnecessarily, as we had all of
this extra space on the consumer_pos page. Specifically, I was trying to
avoid taxing kernel-producer ringbuffers. If you'd prefer, I can just put
it elsewhere in the struct.
next prev parent reply other threads:[~2022-08-12 16:23 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-08 15:53 [PATCH 1/5] bpf: Clear callee saved regs after updating REG0 David Vernet
2022-08-08 15:53 ` [PATCH 2/5] bpf: Define new BPF_MAP_TYPE_USER_RINGBUF map type David Vernet
2022-08-11 23:22 ` Andrii Nakryiko
2022-08-12 16:21 ` David Vernet
2022-08-11 23:29 ` Andrii Nakryiko
2022-08-12 16:23 ` David Vernet [this message]
2022-08-16 18:43 ` Andrii Nakryiko
2022-08-08 15:53 ` [PATCH 3/5] bpf: Add bpf_user_ringbuf_drain() helper David Vernet
2022-08-08 21:55 ` kernel test robot
2022-08-11 23:22 ` Andrii Nakryiko
2022-08-12 0:01 ` David Vernet
2022-08-12 0:46 ` David Vernet
2022-08-16 18:57 ` Andrii Nakryiko
2022-08-16 22:14 ` David Vernet
2022-08-16 22:59 ` Andrii Nakryiko
2022-08-17 20:24 ` David Vernet
2022-08-17 21:03 ` David Vernet
2022-08-08 15:53 ` [PATCH 4/5] bpf: Add libbpf logic for user-space ring buffer David Vernet
2022-08-11 23:39 ` Andrii Nakryiko
2022-08-12 17:28 ` David Vernet
2022-08-16 19:09 ` Andrii Nakryiko
2022-08-17 14:02 ` David Vernet
2022-08-18 3:05 ` David Vernet
2022-08-08 15:53 ` [PATCH 5/5] selftests/bpf: Add selftests validating the user ringbuf David Vernet
2022-08-08 18:14 ` [PATCH 1/5] bpf: Clear callee saved regs after updating REG0 Joanne Koong
2022-08-08 18:50 ` David Vernet
2022-08-08 23:32 ` Joanne Koong
2022-08-09 12:47 ` David Vernet
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=YvZ+fHcKUnUk8jhc@maniforge.dhcp.thefacebook.com \
--to=void@manifault.com \
--cc=Kernel-team@fb.com \
--cc=andrii.nakryiko@gmail.com \
--cc=andrii@kernel.org \
--cc=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=daniel@iogearbox.net \
--cc=haoluo@google.com \
--cc=joannelkoong@gmail.com \
--cc=john.fastabend@gmail.com \
--cc=jolsa@kernel.org \
--cc=kpsingh@kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=martin.lau@linux.dev \
--cc=sdf@google.com \
--cc=song@kernel.org \
--cc=tj@kernel.org \
--cc=yhs@fb.com \
/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 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).