linux-kernel - Re: [PATCH V3 1/2] xen: Update dm

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Message-ID: <8466d82c-d4ff-8302-2475-ae1acc09da38@suse.com>
Date:   Tue, 25 Jul 2023 09:54:52 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Jan Beulich <jbeulich@...e.com>,
        Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Vincent Guittot <vincent.guittot@...aro.org>,
        Alex Bennée <alex.bennee@...aro.org>,
        stratos-dev@...lists.linaro.org,
        Erik Schilling <erik.schilling@...aro.org>,
        Manos Pitsidianakis <manos.pitsidianakis@...aro.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
Subject: Re: [PATCH V3 1/2] xen: Update dm_op.h from Xen public header

On 25.07.23 09:49, Jan Beulich wrote:
> On 25.07.2023 09:42, Viresh Kumar wrote:
>> On 25-07-23, 09:18, Jan Beulich wrote:
>>> I question that use, btw, but it is not up to me to decide whether to
>>> accept such a layering violation in Linux. dm-op is, as its name says,
>>> for device models to use. Your intended use doesn't fall in that
>>> category, aiui. Imo the present contents of dm_op.h in Linux is indeed
>>> all a kernel is supposed to know about, unless it was to gain in-kernel
>>> device models.
>>
>> Is there any other way by which an interrupt can be raised for the
>> guest VM ? I was only aware of this method and so implemented it like
>> this.
>>
>> I am open to suggestions on this.
> 
> Well. I don't know your requirements. Generally I would suggest using
> event channels, not interrupts, when talking about injecting events
> into guests. If it strictly needs to be an interrupt, then I guess a
> non-dm-op means would need introducing if none already exists.

I think the best way would be to let the user mode device model (i.e. the
backend) construct the dm-op parameters like qemu is doing it and pass it
via the ioctl to the privcmd driver as part of struct privcmd_irqfd. Then
it would be opaque to the kernel like every other dm-op.


Juergen


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