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Re: [Qemu-ppc] [PATCH 3/4] spapr: disable hotplugging without OS
From: |
Greg Kurz |
Subject: |
Re: [Qemu-ppc] [PATCH 3/4] spapr: disable hotplugging without OS |
Date: |
Wed, 24 May 2017 11:28:57 +0200 |
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 :)
> > ---
> > 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)) {
>
pgpSHRoXkjuxY.pgp
Description: OpenPGP digital signature
- [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 <=
- 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, Michael Roth, 2017/05/30
- Re: [Qemu-ppc] [Qemu-devel] [PATCH 3/4] spapr: disable hotplugging without OS, David Gibson, 2017/05/31
- 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, 2017/05/24
[Qemu-ppc] [PATCH 2/4] spapr: add option vector 6, Laurent Vivier, 2017/05/23