lkml.org 
[lkml]   [2021]   [Jul]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 2/2] vfio/mdev: don't warn if ->request is not set
On Tue, 27 Jul 2021 14:32:09 -0300
Jason Gunthorpe <jgg@nvidia.com> wrote:

> On Tue, Jul 27, 2021 at 08:04:16AM +0200, Cornelia Huck wrote:
> > On Mon, Jul 26 2021, Alex Williamson <alex.williamson@redhat.com> wrote:
> >
> > > On Mon, 26 Jul 2021 20:09:06 -0300
> > > Jason Gunthorpe <jgg@nvidia.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?

The CCW implementation (likewise the vfio-pci implementation) owns the
IRQ index address space and the decision to make this a signal to
userspace rather than perhaps some handling a device might be able to
do internally. For instance an alternate vfio-pci implementation might
zap all mmaps, block all r/w access, and turn this into a surprise
removal. Another implementation might be more aggressive to sending
SIGKILL to the user process. This was the thought behind why vfio-core
triggers the driver request callback with a counter, leaving the policy
to the driver.

> Is PCI doing the same?

Yes, that's where this handling originated. Thanks,

Alex

\
 
 \ /
  Last update: 2021-07-27 20:53    [W:0.069 / U:0.368 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site