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Re: [PATCH 0/8] Add support for pvpanic mmio device

From: Mihai Carabas
Subject: Re: [PATCH 0/8] Add support for pvpanic mmio device
Date: Mon, 26 Oct 2020 15:50:59 +0200
User-agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.12.1

On 10/22/2020 1:17 PM, Peter Maydell wrote:
On Thu, 22 Oct 2020 at 09:25, Mihai Carabas <mihai.carabas@oracle.com> wrote:
The patchset was assembled from chuncks from some old patches from 2018 [1]
which were left unmerged and some additions from me. Surprisingly their Linux
kernel counterpart were merged (so the pvpanic driver from the kernel supports

I have seen the discussions about moving the pvpanic to PCI [1]. Those patches
were sent but nothing happened. Also they are not trivial and require major
modifications at the driver level also. Given the fact that we already have
mmio driver support for pvpanic in the Linux kernel, I have sent these patches
to ask again the maintainers if this can be merged.

I'm afraid the answer is still the same. You need to provide
a convincing argument for why this needs to be an MMIO
device rather than a PCI device. I really don't want to
add MMIO devices to the virt board if I can avoid it,
because they're all extra code and potential extra
security boundary attack surface. PCI devices are guest
probeable and user-pluggable so they're almost always
nicer to use than MMIO.

Thank you for your input.

The reason why pvpanic should be MMIO is that is a special device which is not used commonly by the user (aka VM), it is not need to be hot-plugable and it does not have a hardware correspondent to be a PCI device. Another reason is that MMIO support was accepted in the kernel driver and it is pretty useless there without a device.

I know it seems that I want to get this on the short-path, but at this point having a kernel driver in the upstream and no device to test it against it is pretty weird.

Thank you,

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