Subject: Re: Questions on the task isolation patches
To: Paolo Bonzini <pbonzini@redhat.com>,
        yunhong jiang <yunhong.jiang@linux.intel.com>
References: <20161201142812.369f23f8@jnakajim-build>
 <5dd4cbf7-d0c0-074a-c5bc-e2e09ec3dc75@mellanox.com>
 <20161206134355.193c752b@jnakajim-build>
 <fe787860-facb-7605-5279-d6b48af96817@mellanox.com>
 <050e5bb5-b5d3-86a4-f7ff-5f633a4bd2bc@redhat.com>
CC: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
From: Chris Metcalf <cmetcalf@mellanox.com>
Message-ID: <65187421-39c8-617f-56bd-d6bd69dfbaee@mellanox.com>
Date: Thu, 22 Dec 2016 15:56:57 -0500
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On 12/20/2016 4:27 AM, Paolo Bonzini wrote:
> On 16/12/2016 22:00, Chris Metcalf wrote:
>> Sorry, I think I wasn't clear.  Normally when you are running task
>> isolated and you enter the kernel, you will get a fatal signal.  The
>> exception is if you call prctl itself (or exit), the kernel tolerates
>> it without a signal, since obviously that's how you need to cleanly
>> tell the kernel you are done with task isolation.
> Running in a guest is pretty much the same as running in userspace.
> Would it be possible to exclude the KVM_RUN ioctl as well?  QEMU would
> still have to run prctl when a CPU goes to sleep, and KVM_RUN would have
> to enable/disable isolated mode when a VM executes HLT (which should
> never happen anyway in NFV scenarios).

I think that probably makes sense.  The flow would be that qemu executes
first the prctl() for task isolation, then the KVM_RUN ioctl.  We obviously can't
do it in the other order, so we'd need to make task isolation tolerate KVM_RUN.

I won't try to do it for my next patch series (based on 4.10) though, since I'd
like to get the basic support upstreamed before trying to extend it.

-- 
Chris Metcalf, Mellanox Technologies
http://www.mellanox.com