linux-kernel - Re: [PATCH 0/2] virtio-balloon: make it spec compliant

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Message-ID: <df74b121-c0fd-41e1-b42f-64dd73ace352@redhat.com>
Date: Wed, 10 Jul 2024 05:09:16 +0200
From: David Hildenbrand <david@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: linux-kernel@...r.kernel.org,
 Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 0/2] virtio-balloon: make it spec compliant

Sorry for the late reply!

>> I understand that concern, IIUC it would imply that:
>>
>> a) In case of a hypervisor, we never ran with a Linux guest
>> b) In case of a guest, we never ran under QEMU
> 
> Or maybe VIRTIO_BALLOON_F_FREE_PAGE_HINT is set.

Right, in which case it would be according to the spec.

>> It's certainly possible, although I would assume that most other
>> implementation candidates (e.g., cloud-hypervisor) would have complained by
>> now about Linux issues.
> 
> They either set VIRTIO_BALLOON_F_FREE_PAGE_HINT or followed linux bug to
> work around.

Okay, in the latter case it would be the unofficial way of doing it.

>> What's your experience: if someone would actually implement it according to
>> the spec, would they watch out on the virtio mailing lists for changes (or
>> even be able to vote) and would be able to comment that adjusting the spec
>> to the real first implementation is wrong?
> 
> Unfortunately my experience is that it's not that likely :(

That's what I thought, unfortunately.

> 
> 
> Whatever we do, we need to take existing setups into account.
> 
> How would we do it in the spec without breaking working setups?  I guess
> we could say that both behaviours are legal.  That would still mean we
> need the qemu and linux patches, right?

That makes sense to me. Let me take a look at the patches.

-- 
Cheers,

David / dhildenb