linux-kernel - Re: [RFC PATCH for 4.16 02/21] rseq: Introduce restartable sequences system call (v12)

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1772818221.34575.1513281428902.JavaMail.zimbra@efficios.com>
Date:   Thu, 14 Dec 2017 19:57:08 +0000 (UTC)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Chris Lameter <cl@...ux.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Andy Lutomirski <luto@...capital.net>,
        Dave Watson <davejwatson@...com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-api <linux-api@...r.kernel.org>,
        Paul Turner <pjt@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Russell King <linux@....linux.org.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Andrew Hunter <ahh@...gle.com>,
        Andi Kleen <andi@...stfloor.org>, Ben Maurer <bmaurer@...com>,
        rostedt <rostedt@...dmis.org>,
        Josh Triplett <josh@...htriplett.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [RFC PATCH for 4.16 02/21] rseq: Introduce restartable
 sequences system call (v12)

----- On Dec 14, 2017, at 2:48 PM, Peter Zijlstra peterz@...radead.org wrote:

> On Thu, Dec 14, 2017 at 12:50:13PM -0600, Christopher Lameter wrote:
>> Ultimately I wish fast increments like done by this_cpu_inc() could be
>> implemented in an efficient way on non x86 platforms that do not have
>> cheap instructions like that.
> 
> So the problem isn't migration; for that we could wrap the operation in
> preempt_disable() which is not more expensive than rseq would be. And a
> lot more deterministic.
> 
> The problem instead is interrupts, which can result in nested load-store
> operations, and that comes apart. This then means having to disable
> interrupts over these things and _that_ is expensive.

Then could we consider checking a per task-struct rseq_cs pointer when
returning from interrupt handler ? This rseq_cs pointer would track
kernel restartable sequences. This would also work for NMI handlers.

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com