Re: [PATCH v2] ptrace: add PTRACE_GET_RSEQ_CONFIGURATION request

From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Piotr Figiel <figiel@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	paulmck <paulmck@kernel.org>, Boqun Feng <boqun.feng@gmail.com>,
	Oleg Nesterov <oleg@redhat.com>,
	"Dmitry V. Levin" <ldv@altlinux.org>,
	Florian Weimer <fweimer@redhat.com>,
	Alexey Dobriyan <adobriyan@gmail.com>,
	Andrei Vagin <avagin@gmail.com>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Peter Oskolkov <posk@google.com>,
	Kamil Yurtsever <kyurtsever@google.com>,
	Chris Kennelly <ckennelly@google.com>,
	Paul Turner <pjt@google.com>, emmir <emmir@google.com>,
	linux-man <linux-man@vger.kernel.org>,
	linux-api <linux-api@vger.kernel.org>
Subject: Re: [PATCH v2] ptrace: add PTRACE_GET_RSEQ_CONFIGURATION request
Date: Thu, 11 Mar 2021 12:24:44 -0500 (EST)	[thread overview]
Message-ID: <1972946676.5785.1615483484807.JavaMail.zimbra@efficios.com> (raw)
In-Reply-To: <YEpKoa9PgjffO7Q5@hirez.programming.kicks-ass.net>

----- On Mar 11, 2021, at 11:51 AM, Peter Zijlstra peterz@infradead.org wrote:

> On Thu, Mar 11, 2021 at 09:51:56AM -0500, Mathieu Desnoyers wrote:
>> 
>> 
>> ----- On Feb 26, 2021, at 8:51 AM, Piotr Figiel figiel@google.com wrote:
>> 
>> > For userspace checkpoint and restore (C/R) a way of getting process state
>> > containing RSEQ configuration is needed.
>> > 
>> > There are two ways this information is going to be used:
>> > - to re-enable RSEQ for threads which had it enabled before C/R
>> > - to detect if a thread was in a critical section during C/R
>> > 
>> > Since C/R preserves TLS memory and addresses RSEQ ABI will be restored
>> > using the address registered before C/R.
>> > 
>> > Detection whether the thread is in a critical section during C/R is needed
>> > to enforce behavior of RSEQ abort during C/R. Attaching with ptrace()
>> > before registers are dumped itself doesn't cause RSEQ abort.
>> > Restoring the instruction pointer within the critical section is
>> > problematic because rseq_cs may get cleared before the control is passed
>> > to the migrated application code leading to RSEQ invariants not being
>> > preserved. C/R code will use RSEQ ABI address to find the abort handler
>> > to which the instruction pointer needs to be set.
>> > 
>> > To achieve above goals expose the RSEQ ABI address and the signature value
>> > with the new ptrace request PTRACE_GET_RSEQ_CONFIGURATION.
>> > 
>> > This new ptrace request can also be used by debuggers so they are aware
>> > of stops within restartable sequences in progress.
>> > 
>> > Signed-off-by: Piotr Figiel <figiel@google.com>
>> > Reviewed-by: Michal Miroslaw <emmir@google.com>
>> 
>> Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> 
> How do we route this? Do I stick this in tip/sched/core as being an rseq
> patch?

Sure, it's fine with me, thanks!

Mathieu

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