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Date: Mon, 17 Mar 2014 15:49:17 +0100
From: Laszlo Ersek <lersek@redhat.com>
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Subject: Re: [Qemu-devel] virtio device error reporting best practice?
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: Dave Airlie <airlied@gmail.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, Seiji Aguchi <saguchi@redhat.com>

On 03/17/14 15:40, Peter Maydell wrote:
> On 17 March 2014 14:28, Laszlo Ersek <lersek@redhat.com> wrote:
>> On 03/17/14 07:02, Dave Airlie wrote:
>>> The main reason I'm considering this stuff is for security reasons if
>>> the guest asks for something really illegal or crazy what should the
>>> expected behaviour of the host be? (at least secure I know that).
>>
>> exit(1).
> 
> No thanks -- the guest should never be able to cause QEMU
> to exit (in an ideal world). Use
>    qemu_log_mask(LOG_GUEST_ERROR, ...)
> and continue.

How do you continue with a garbled virtio ring? Say you detect an error
that would cause integer overflow or buffer overflow in the host, a
clear virtio protocol violation etc. Error reporting is just one thing
-- what are the semantics of continuing?

Exit(1) is considered guest crash. "The guest should never be able to
cause QEMU to exit" is identical to "a bare metal kernel should never be
able to crash a physical machine, even if it wants to". Some behavior is
left undefined even in hardware manuals. Crashing as early as possible
is safe and helpful.

Just my opinion, naturally.

Thanks,
Laszlo