From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Florian Weimer <fweimer@redhat.com>
Cc: "Peter Zijlstra" <peterz@infradead.org>,
linux-kernel@vger.kernel.org,
"Thomas Gleixner" <tglx@linutronix.de>,
"Paul E . McKenney" <paulmck@kernel.org>,
"Boqun Feng" <boqun.feng@gmail.com>,
"H . Peter Anvin" <hpa@zytor.com>, "Paul Turner" <pjt@google.com>,
linux-api@vger.kernel.org,
"Christian Brauner" <brauner@kernel.org>,
David.Laight@ACULAB.COM, carlos@redhat.com,
"Peter Oskolkov" <posk@posk.io>,
"Alexander Mikhalitsyn" <alexander@mihalicyn.com>,
"Chris Kennelly" <ckennelly@google.com>,
"Ingo Molnar" <mingo@redhat.com>,
"Darren Hart" <dvhart@infradead.org>,
"Davidlohr Bueso" <dave@stgolabs.net>,
"André Almeida" <andrealmeid@igalia.com>,
libc-alpha@sourceware.org, "Steven Rostedt" <rostedt@goodmis.org>,
"Jonathan Corbet" <corbet@lwn.net>,
"Noah Goldstein" <goldstein.w.n@gmail.com>,
longman@redhat.com, "Olivier Dion" <odion@efficios.com>
Subject: Re: [RFC PATCH v2 1/4] rseq: Add sched_state field to struct rseq
Date: Tue, 30 May 2023 11:13:41 -0400 [thread overview]
Message-ID: <c1064e76-70f8-4a5f-2624-95a1e2dc9d64@efficios.com> (raw)
In-Reply-To: <b0416e8c-9b8f-9b25-dd0c-3b7882e5746f@efficios.com>
On 5/30/23 10:25, Mathieu Desnoyers wrote:
> On 5/30/23 04:20, Florian Weimer wrote:
[...]
>>
>> The challenge is that once we put stuff at fixed offsets, we can't
>> transparently fix it later. It would need more auxv entries with
>> further offsets, or accessing this data through some indirection,
>> perhaps via vDSO helpers.
>
> Perhaps this is more flexibility/complexity than we really need. One
> possible approach would be to split struct rseq into sub-structures, e.g.:
>
> rseq_len = overall size of all sub-structures.
> auxv AT_RSEQ_ALIGN = 256
>
> auxv AT_RSEQ_FEATURE_SIZE = size of first portion of struct rseq,
> at most 256 bytes, meant to contain fields
> stored/loaded from the thread doing the
> registration.
> auxv AT_RSEQ_SHARED_FEATURE_SIZE =
> size of 2nd portion of struct rseq,
> starts at offset 256, at most 256 bytes,
> meant to contain fields stored/loaded by
> any thread.
>
> Then we have this layout:
>
> struct rseq {
> struct rseq_local {
> /* Fields accessed from local thread. */
>
> } __attribute__((aligned((256));
> struct rseq_shared {
> /* Shared fields. */
>
> } __attribute__((aligned(256));
> } __attribute__((aligned(256));
>
> And if someday AT_RSEQ_FEATURE_SIZE needs to grow over 256 bytes
> (32 * u64), we can still extend with a new auxv entry after the "shared"
> features.
Actually, after giving it some more thoughts, I think we can do better:
- Add a sys_rseq() rseq_flag RSEQ_FLAG_SHARED, which changes the
behavior of sys_rseq() to expect an additional "struct rseq_shared *"
argument.
- Introduce auxv AT_RSEQ_SHARED_FEATURE_SIZE.
This way, it's up to the libc to decide how to allocate its private vs
shared rseq structures.
The auxv "AT_RSEQ_ALIGN" would dictate the minimal alignment required
for both private and shared rseq structures.
I don't think we need to express the size of the rseq_shared memory area
allocated by libc because we know that it needs to be large enough to
handle the shared feature size.
Thoughts ?
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
next prev parent reply other threads:[~2023-05-30 15:13 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-29 19:14 [RFC PATCH v2 0/4] Extend rseq with sched_state_ptr field Mathieu Desnoyers
2023-05-29 19:14 ` [RFC PATCH v2 1/4] rseq: Add sched_state field to struct rseq Mathieu Desnoyers
2023-05-29 19:35 ` Florian Weimer
2023-05-29 19:48 ` Mathieu Desnoyers
2023-05-30 8:20 ` Florian Weimer
2023-05-30 14:25 ` Mathieu Desnoyers
2023-05-30 15:13 ` Mathieu Desnoyers [this message]
2023-09-26 20:52 ` Dmitry Vyukov
2023-09-26 23:49 ` Dmitry Vyukov
2023-09-26 23:54 ` Dmitry Vyukov
2023-09-27 4:51 ` Florian Weimer
2023-09-27 15:58 ` Dmitry Vyukov
2023-09-28 8:52 ` Florian Weimer
2023-09-28 14:44 ` Dmitry Vyukov
2023-09-28 14:47 ` Dmitry Vyukov
2023-09-28 10:39 ` Peter Zijlstra
2023-09-28 11:22 ` David Laight
2023-09-28 13:20 ` Mathieu Desnoyers
2023-09-28 14:26 ` Peter Zijlstra
2023-09-28 14:33 ` David Laight
2023-09-28 15:05 ` André Almeida
2023-09-28 14:43 ` Steven Rostedt
2023-09-28 15:51 ` David Laight
2023-10-02 16:51 ` Steven Rostedt
2023-10-02 17:22 ` David Laight
2023-10-02 17:56 ` Steven Rostedt
2023-09-28 20:21 ` Thomas Gleixner
2023-09-28 20:43 ` Mathieu Desnoyers
2023-09-28 20:54 ` Thomas Gleixner
2023-09-28 22:11 ` Mathieu Desnoyers
2023-05-29 19:14 ` [RFC PATCH v2 2/4] selftests/rseq: Add sched_state rseq field and getter Mathieu Desnoyers
2023-05-29 19:14 ` [RFC PATCH v2 3/4] selftests/rseq: Implement sched state test program Mathieu Desnoyers
2023-05-29 19:14 ` [RFC PATCH v2 4/4] selftests/rseq: Implement rseq_mutex " Mathieu Desnoyers
2023-09-28 19:55 ` Thomas Gleixner
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