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Re: [PATCH 0/3] spapr: Fix device unplug vs CAS or migration

From: David Gibson
Subject: Re: [PATCH 0/3] spapr: Fix device unplug vs CAS or migration
Date: Fri, 14 Feb 2020 13:29:25 +1100

On Thu, Feb 13, 2020 at 04:10:55PM +0100, Greg Kurz wrote:
> Ping ?
> This series fixes actual bugs. Also, I have another patch on top of
> that to cold plug (or remove) devices pending hot plug (or unplug)
> before CAS, hence removing the need for CAS reboot in these cases.
> This requires SLOF to correctly parse the FDT it gets at CAS. Patches
> have been sent for that too:
> https://git.qemu.org/?p=SLOF.git;a=commitdiff;h=689ff6f6554d94fdab854bf4fc4ec85e2675e43d
> https://git.qemu.org/?p=SLOF.git;a=commitdiff;h=a093be1ebe7a48321646601d94be6cf735c81e12
> https://patchwork.ozlabs.org/patch/1235817/

Yeah, sorry, I've been having a bit of trouble getting my head around
the cases here.  I've sent a comment now.

> On Mon, 03 Feb 2020 23:36:04 +0100
> Greg Kurz <address@hidden> wrote:
> > While working on getting rid of CAS reboot, I realized that we currently
> > don't handle device hot unplug properly in the following situations:
> > 
> > 1) if the device is unplugged between boot and CAS, SLOF doesn't handle
> >    the even, which is a known limitation. The device hence stays around
> >    forever (specifically, until some other event is emitted and the guest
> >    eventually completes the unplug or a reboot). Until we can teach SLOF
> >    to correctly process the full FDT at CAS, we should trigger a CAS reboot,
> >    like we already do for hotplug.
> > 
> > 2) if the guest is migrated after the even was emitted but before the
> >    guest could process it, the destination is unaware of the pending
> >    unplug operation and doesn't remove the device when the guests
> >    releases it. The 'unplug_requested' field of the DRC is actually state
> >    that should be migrated.
> > 

David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!

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