linux-kernel - Re: [PATCH V3 2/4] misc: vop: do not allocate and reassign the used ring

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Message-ID: <20201028091410.o2odlqrhzzbiqh44@axis.com>
Date:   Wed, 28 Oct 2020 10:14:10 +0100
From:   Vincent Whitchurch <vincent.whitchurch@...s.com>
To:     Sherry Sun <sherry.sun@....com>
CC:     "sudeep.dutt@...el.com" <sudeep.dutt@...el.com>,
        "ashutosh.dixit@...el.com" <ashutosh.dixit@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "arnd@...db.de" <arnd@...db.de>, "kishon@...com" <kishon@...com>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: Re: [PATCH V3 2/4] misc: vop: do not allocate and reassign the used
 ring

On Wed, Oct 28, 2020 at 02:47:49AM +0100, Sherry Sun wrote:
> > Subject: Re: [PATCH V3 2/4] misc: vop: do not allocate and reassign the used
> > ring
> > 
> > On Tue, Oct 27, 2020 at 08:05:43AM +0100, Sherry Sun wrote:
> > > Can you help test the patch about removing the codes of reassign used
> > > ring, and comment on the impact for Intel MIC platform?  Thanks for
> > > any help.
> > 
> > I don't have access to MIC hardware myself, either.
> > 
> > But this patch is quite certainly going to break it since guests using a kernel
> > without the patch will not work with hosts with a kernel with the patch.
> 
> Thanks for your reply.
> This patch can be used by both guests and hosts.
> I have tested it on imx8qm platform(both guest and host are ARM64 architecture), and it works well.
> So I guess Intel MIC won't meet big problems when both guest and host
> apply this patch. But it is best if it can be tested.

The guest and host are different systems and it should be possible to
upgrade the host kernel without being forced to upgrade the guest
kernel, and vice-versa.  This patch breaks that.

If MIC hardware has no users and the drivers are being deleted then of
course backward compatibility doesn't matter.