linux-kernel - Re: [PATCH v15 08/13] arch/arm64: enable task isolation functionality

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Date:   Fri, 26 Aug 2016 17:25:16 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Chris Metcalf <cmetcalf@...lanox.com>
Cc:     Gilad Ben Yossef <giladb@...lanox.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Rik van Riel <riel@...hat.com>, Tejun Heo <tj@...nel.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Christoph Lameter <cl@...ux.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Will Deacon <will.deacon@....com>,
        Andy Lutomirski <luto@...capital.net>,
        Mark Rutland <mark.rutland@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v15 08/13] arch/arm64: enable task isolation functionality

On Tue, Aug 16, 2016 at 05:19:31PM -0400, Chris Metcalf wrote:
> In do_notify_resume(), call task_isolation_ready() for
> TIF_TASK_ISOLATION tasks when we are checking the thread-info flags;
> and after we've handled the other work, call task_isolation_enter()
> for such tasks.  To ensure we always call task_isolation_enter() when
> returning to userspace, add _TIF_TASK_ISOLATION to _TIF_WORK_MASK,
> while leaving the old bitmask value as _TIF_WORK_LOOP_MASK to
> check while looping.
> 
> We tweak syscall_trace_enter() slightly to carry the "flags"
> value from current_thread_info()->flags for each of the tests,
> rather than doing a volatile read from memory for each one.  This
> avoids a small overhead for each test, and in particular avoids
> that overhead for TIF_NOHZ when TASK_ISOLATION is not enabled.
> 
> We instrument the smp_send_reschedule() routine so that it checks for
> isolated tasks and generates a suitable warning if we are about
> to disturb one of them in strict or debug mode.
> 
> Finally, report on page faults in task-isolation processes in
> do_page_faults().
> 
> Signed-off-by: Chris Metcalf <cmetcalf@...lanox.com>
> ---
>  arch/arm64/Kconfig                   |  1 +
>  arch/arm64/include/asm/thread_info.h |  5 ++++-
>  arch/arm64/kernel/ptrace.c           | 18 +++++++++++++++---
>  arch/arm64/kernel/signal.c           | 10 ++++++++++
>  arch/arm64/kernel/smp.c              |  2 ++
>  arch/arm64/mm/fault.c                |  8 +++++++-

Not sure when/how this series will be merged (Will already picked patch
07/13 as a general clean-up) but this arm64 patch:

Reviewed-by: Catalin Marinas <catalin.marinas@....com>