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Re: [Qemu-ppc] [PATCH 3/4] spapr: disable hotplugging without OS
From: |
David Gibson |
Subject: |
Re: [Qemu-ppc] [PATCH 3/4] spapr: disable hotplugging without OS |
Date: |
Thu, 25 May 2017 12:45:34 +1000 |
User-agent: |
Mutt/1.8.0 (2017-02-23) |
On Wed, May 24, 2017 at 11:28:57AM +0200, Greg Kurz wrote:
> On Wed, 24 May 2017 15:07:54 +1000
> David Gibson <address@hidden> wrote:
>
> > On Tue, May 23, 2017 at 01:18:11PM +0200, Laurent Vivier wrote:
> > > If the OS is not started, QEMU sends an event to the OS
> > > that is lost and cannot be recovered. An unplug is not
> > > able to restore QEMU in a coherent state.
> > > So, while the OS is not started, disable CPU and memory hotplug.
> > > We use option vector 6 to know if the OS is started
> > >
> > > Signed-off-by: Laurent Vivier <address@hidden>
> >
> > Urgh.. I'm not terribly confident that this is really correct. As
> > discussed on the previous patch, you're essentially using OV6 as a
> > flag that CAS is complete.
> >
> > But while it undoubtedly makes the race window much smaller, I don't
> > see that there's any guarantee the guest OS will really be able to
> > handle hotplug events immediately after CAS.
> >
> > In particular if the CAS process completes partially but then needs to
> > trigger a reboot, I think that would end up setting the ov6 variable,
> > but the OS would definitely not be in a state to accept events.
> >
>
> We never have any guarantee that the OS will process an event that
> we've sent actually (think of a kernel crash just after a successful
> CAS negotiation for example, or any failure with the various guest
> components involved in the process of hotplug).
>
> > Mike, I really think we need some input from someone familiar with how
> > these hotplug events are supposed to work. What do we need to do to
> > handle lost or stale events, such as those delivered when an OS is not
> > booted.
> >
>
> AFAIK, in the PowerVM world, the HMC exposes a user configurable timeout.
>
> https://www.ibm.com/support/knowledgecenter/POWER8/p8hat/p8hat_dlparprocpoweraddp6.htm
>
> I'm not sure we can do anything better than being able to "cancel" a previous
> hotplug attempt if it takes too long, but I'm not necessarily the expert
> you're
> looking for :)
Right, but at the moment we *don't* have a way to cancel a previous
hotplug attempt. Trying to remove again ends up with things in a
tangle.
>
> > > ---
> > > hw/ppc/spapr.c | 22 +++++++++++++++++++---
> > > 1 file changed, 19 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > > index eceb4cc..2e9320d 100644
> > > --- a/hw/ppc/spapr.c
> > > +++ b/hw/ppc/spapr.c
> > > @@ -2625,6 +2625,7 @@ out:
> > > static void spapr_memory_pre_plug(HotplugHandler *hotplug_dev,
> > > DeviceState *dev,
> > > Error **errp)
> > > {
> > > + sPAPRMachineState *ms = SPAPR_MACHINE(hotplug_dev);
> > > PCDIMMDevice *dimm = PC_DIMM(dev);
> > > PCDIMMDeviceClass *ddc = PC_DIMM_GET_CLASS(dimm);
> > > MemoryRegion *mr = ddc->get_memory_region(dimm);
> > > @@ -2645,6 +2646,13 @@ static void spapr_memory_pre_plug(HotplugHandler
> > > *hotplug_dev, DeviceState *dev,
> > > goto out;
> > > }
> > >
> > > + if (dev->hotplugged) {
> > > + if (!ms->os_name) {
> > > + error_setg(&local_err, "Memory hotplug not supported without
> > > OS");
> > > + goto out;
> > > + }
> > > + }
> > > +
> > > out:
> > > error_propagate(errp, local_err);
> > > }
> > > @@ -2874,6 +2882,7 @@ static void spapr_core_pre_plug(HotplugHandler
> > > *hotplug_dev, DeviceState *dev,
> > > Error **errp)
> > > {
> > > MachineState *machine = MACHINE(OBJECT(hotplug_dev));
> > > + sPAPRMachineState *ms = SPAPR_MACHINE(machine);
> > > MachineClass *mc = MACHINE_GET_CLASS(hotplug_dev);
> > > Error *local_err = NULL;
> > > CPUCore *cc = CPU_CORE(dev);
> > > @@ -2884,9 +2893,16 @@ static void spapr_core_pre_plug(HotplugHandler
> > > *hotplug_dev, DeviceState *dev,
> > > int node_id;
> > > int index;
> > >
> > > - if (dev->hotplugged && !mc->has_hotpluggable_cpus) {
> > > - error_setg(&local_err, "CPU hotplug not supported for this
> > > machine");
> > > - goto out;
> > > + if (dev->hotplugged) {
> > > + if (!mc->has_hotpluggable_cpus) {
> > > + error_setg(&local_err,
> > > + "CPU hotplug not supported for this machine");
> > > + goto out;
> > > + }
> > > + if (!ms->os_name) {
> > > + error_setg(&local_err, "CPU hotplug not supported without
> > > OS");
> > > + goto out;
> > > + }
> > > }
> > >
> > > if (strcmp(base_core_type, type)) {
> >
>
--
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_!
http://www.ozlabs.org/~dgibson
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- [Qemu-ppc] [PATCH 0/4] spapr: disable hotplugging without OS, Laurent Vivier, 2017/05/23
- [Qemu-ppc] [PATCH 3/4] spapr: disable hotplugging without OS, Laurent Vivier, 2017/05/23
- Re: [Qemu-ppc] [PATCH 3/4] spapr: disable hotplugging without OS, David Gibson, 2017/05/24
- Re: [Qemu-ppc] [PATCH 3/4] spapr: disable hotplugging without OS, Greg Kurz, 2017/05/24
- Re: [Qemu-ppc] [Qemu-devel] [PATCH 3/4] spapr: disable hotplugging without OS, Igor Mammedov, 2017/05/24
- Re: [Qemu-ppc] [Qemu-devel] [PATCH 3/4] spapr: disable hotplugging without OS, Greg Kurz, 2017/05/24
- Re: [Qemu-ppc] [Qemu-devel] [PATCH 3/4] spapr: disable hotplugging without OS, Laurent Vivier, 2017/05/24
- Re: [Qemu-ppc] [Qemu-devel] [PATCH 3/4] spapr: disable hotplugging without OS, Michael Roth, 2017/05/24
- Re: [Qemu-ppc] [Qemu-devel] [PATCH 3/4] spapr: disable hotplugging without OS, David Gibson, 2017/05/24
- Re: [Qemu-ppc] [Qemu-devel] [PATCH 3/4] spapr: disable hotplugging without OS, David Gibson, 2017/05/24
- Re: [Qemu-ppc] [PATCH 3/4] spapr: disable hotplugging without OS,
David Gibson <=
[Qemu-ppc] [PATCH 2/4] spapr: add option vector 6, Laurent Vivier, 2017/05/23
[Qemu-ppc] [PATCH 1/4] spapr: add pre_plug function for memory, Laurent Vivier, 2017/05/23
[Qemu-ppc] [PATCH 4/4] Revert "spapr: fix memory hot-unplugging", Laurent Vivier, 2017/05/23