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Re: [Qemu-ppc] [PATCH] spapr: fix core unplug crash
From: |
Greg Kurz |
Subject: |
Re: [Qemu-ppc] [PATCH] spapr: fix core unplug crash |
Date: |
Fri, 8 Jul 2016 17:47:01 +0200 |
On Fri, 08 Jul 2016 15:12:07 +0200
Greg Kurz <address@hidden> wrote:
> If the host has 8 threads/core and the guest is started with:
>
> -smp cores=1,threads=4,maxcpus=12
>
> It is possible to crash QEMU by doing:
>
> (qemu) device_add host-spapr-cpu-core,core-id=16,id=foo
> (qemu) device_del foo
> Segmentation fault
>
> This is caused because spapr_core_unplug() assumes cpu_dt_id == core_id.
> Even if it happens to be the case when the host and guest have the same
> number of threads per core, it is conceptually wrong and we may pass a
> bogus id to spapr_dr_connector_by_id() and spapr_core_release() crashes.
>
> Let's use cc->core_id, which is the id that was used to create th DR
> connector.
My bad, I got excited and pointed out the wrong culprit... it is cpu_index
again of course ! Please find an updated explanation to be put in the
changelog after "Segmentation fault":
========================================================================
This happens because spapr_core_unplug() assumes cpu_dt_id == core_id.
As long as cpu_dt_id is derived from the non-table cpu_index, this is
only true when you plug cores with contiguous ids.
It is safer to be consistent: the DR connector was created with an
index that is immediately written to cc->core_id, and spapr_core_plug()
also relies on cc->core_id.
Let's use it also in spapr_core_unplug().
========================================================================
>
> Signed-off-by: Greg Kurz <address@hidden>
> ---
> hw/ppc/spapr_cpu_core.c | 6 ++----
> 1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/hw/ppc/spapr_cpu_core.c b/hw/ppc/spapr_cpu_core.c
> index 70b6b0b5ee17..106eaf45b399 100644
> --- a/hw/ppc/spapr_cpu_core.c
> +++ b/hw/ppc/spapr_cpu_core.c
> @@ -126,11 +126,9 @@ static void spapr_core_release(DeviceState *dev, void
> *opaque)
> void spapr_core_unplug(HotplugHandler *hotplug_dev, DeviceState *dev,
> Error **errp)
> {
> - sPAPRCPUCore *core = SPAPR_CPU_CORE(OBJECT(dev));
> - PowerPCCPU *cpu = POWERPC_CPU(core->threads);
> - int id = ppc_get_vcpu_dt_id(cpu);
> + CPUCore *cc = CPU_CORE(dev);
> sPAPRDRConnector *drc =
> - spapr_dr_connector_by_id(SPAPR_DR_CONNECTOR_TYPE_CPU, id);
> + spapr_dr_connector_by_id(SPAPR_DR_CONNECTOR_TYPE_CPU, cc->core_id);
> sPAPRDRConnectorClass *drck;
> Error *local_err = NULL;
>
>
>