Re: [Qemu-devel] [PATCH V10 7/9] hw/misc/pvpanic: preparing foradding configure interface

From: Peter Maydell <peter.maydell@linaro.org>
To: Peng Hao <peng.hao2@zte.com.cn>
Cc: "Andrew Jones" <drjones@redhat.com>,
	qemu-arm <qemu-arm@nongnu.org>,
	"Philippe Mathieu-Daudé" <philmd@redhat.com>,
	"QEMU Developers" <qemu-devel@nongnu.org>
Subject: Re: [Qemu-devel] [PATCH V10 7/9] hw/misc/pvpanic: preparing foradding configure interface
Date: Sat, 1 Dec 2018 12:05:02 +0000	[thread overview]
Message-ID: <CAFEAcA-0DPo=4vzHtfD-bmAsfguOd7RiQUnHMpg0Q0e8aNZ_vA@mail.gmail.com> (raw)
In-Reply-To: <201812011728499706543@zte.com.cn>

On Sat, 1 Dec 2018 at 09:28, <peng.hao2@zte.com.cn> wrote:
> Peter Maydell wrote:
> >This kind of thing is why a PCI device is cleaner -- it just
> >works on any machine with a PCI controller, it by default is
> >something that the user can provide if they want to and not if
> >they don't, and it's not a custom UI that management layers
> >might need to special-case. The guest does need to do a bit
> >of PCI probing and setup initially, but then it can just leave
> >the MMIO BAR permanently mapped and write to that address
> >when the guest panics.

> Usually, it doesn't matter if there is this pvpanic device or not, so I
> haven't considered configurability from the beginning.

It matters to people who don't want it, because it increases
the attack surface presented to the guest.

>  I didn't expect you to strongly recommend the use of PCI devices.
> Doing so is not just going to roll back some of the code in the kernel...
> I'll think about your suggestions.

My view on this hasn't changed since October:
https://lists.nongnu.org/archive/html/qemu-devel/2018-10/msg03861.html
if this really really needs to be an MMIO device then it can
be done, but a PCI device is a much cleaner interface which
is more widely usable than just the virt board.

thanks
-- PMM