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

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Date:   Tue, 27 Jul 2021 14:32:09 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Cornelia Huck <cohuck@...hat.com>
Cc:     Alex Williamson <alex.williamson@...hat.com>,
        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 Tue, Jul 27, 2021 at 08:04:16AM +0200, Cornelia Huck wrote:
> 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.

If it is a dedicated eventfd for 'device being removed' why is it in
the CCW implementation and not core code?

Is PCI doing the same?

Jason