Re: [PATCH 6/6] pcie: expire pending delete

[Michael S. Tsirkin]

On Tue, Oct 12, 2021 at 07:30:34AM +0200, Gerd Hoffmann wrote:
> > > index f3ac04399969..477c8776aa27 100644
> > > --- a/hw/pci/pcie.c
> > > +++ b/hw/pci/pcie.c
> > > @@ -549,6 +549,8 @@ void pcie_cap_slot_unplug_request_cb(HotplugHandler 
> > > *hotplug_dev,
> > >      }
> > >  
> > >      dev->pending_deleted_event = true;
> > > +    dev->pending_deleted_expires_ms =
> > > +        qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL) + 5000; /* 5 secs */
> > >  
> > >      /* In case user cancel the operation of multi-function hot-add,
> > >       * remove the function that is unexposed to guest individually,
> > 
> > 
> > Well this will be barely enough, right?
> > 
> >     Once the Power
> >     Indicator begins blinking, a 5-second abort interval exists during 
> > which a second depression of the
> >     Attention Button cancels the operation.
> 
> Well, canceling the hot-plug is not supported in qemu right now (there
> is no qmp command for that).  I'm also not sure it makes sense in the
> first place for virtual machines.

Yes. However if you resend an attention button press within the
5 second window, guest will think you cancelled hot-plug
and act accordingly.
It's a fundamentally racy algorithm :(


> > So I guess it needs to be more. Problem is of course if guest is
> > busy because of interrupts and whatnot, it might not get to
> > handling that in time ...
> 
> See patch #3, that one should take care of a busy guest ...
> 
> take care,
>   Gerd