linux-kernel - Re: [PATCH 2/2] vfio/mdev: don't warn if ->request is not set

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Message-ID: <87wnpc47j3.fsf@redhat.com>
Date:   Tue, 27 Jul 2021 08:04:16 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Alex Williamson <alex.williamson@...hat.com>,
        Jason Gunthorpe <jgg@...dia.com>
Cc:     Christoph Hellwig <hch@....de>,
        Kirti Wankhede <kwankhede@...dia.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] vfio/mdev: don't warn if ->request is not set

On Mon, Jul 26 2021, Alex Williamson <alex.williamson@...hat.com> wrote:

> On Mon, 26 Jul 2021 20:09:06 -0300
> Jason Gunthorpe <jgg@...dia.com> wrote:
>
>> On Mon, Jul 26, 2021 at 07:07:04PM +0200, Cornelia Huck wrote:
>> 
>> > But I wonder why nobody else implements this? Lack of surprise removal?  
>> 
>> The only implementation triggers an eventfd that seems to be the same
>> eventfd as the interrupt..
>> 
>> Do you know how this works in userspace? I'm surprised that the
>> interrupt eventfd can trigger an observation that the kernel driver
>> wants to be unplugged?
>
> I think we're talking about ccw, but I see QEMU registering separate
> eventfds for each of the 3 IRQ indexes and the mdev driver specifically
> triggering the req_trigger...?  Thanks,
>
> Alex

Exactly, ccw has a trigger for normal I/O interrupts, CRW (machine
checks), and this one.