linux-kernel - Re: Ping: [PATCH v15 00/13] support "task

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Date:   Wed, 7 Sep 2016 17:39:26 -0400
From:   Francis Giraldeau <francis.giraldeau@...il.com>
To:     Chris Metcalf <cmetcalf@...lanox.com>,
        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>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Andy Lutomirski <luto@...capital.net>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        linux-doc@...r.kernel.org, linux-api@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: Ping: [PATCH v15 00/13] support "task_isolation" mode

On 2016-09-07 05:11 PM, Francis Giraldeau wrote:
> The syscall test fails on x86:
>     $ sudo ./isolation
>     [...]
>     test_syscall: FAIL (0x100)
>     test_syscall (SIGUSR1): FAIL (0x100)
>
> I wanted to debug this problem with gdb and a KVM virtual machine. However, the TSC clock source is detected as non reliable, even with the boot parameter tsc=reliable, and therefore prctl(PR_SET_TASK_ISOLATION, PR_TASK_ISOLATION_ENABLE) always returns EAGAIN. Is there a trick to run task isolation in a VM (at least for debugging purposes)?

OK, got it. The guest kernel must be compiled with CONFIG_KVM_GUEST, and then with virsh edit, set the clock configuration of the VM (under <domain>):

 <clock offset='utc'>
    <timer name='kvmclock'/>
  </clock>

Of course, the jitter is horrible, but at least it is possible to debug with GDB.

Cheers,

Francis