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[Qemu-devel] [PATCH 6/7] s390x: Limit s390-ccw machines to 248 CPUs

From: Cornelia Huck
Subject: [Qemu-devel] [PATCH 6/7] s390x: Limit s390-ccw machines to 248 CPUs
Date: Wed, 8 Jun 2016 13:02:44 +0200

From: Christian Borntraeger <address@hidden>

The sclp scp read info call fills in a buffer with information about the
system. With more than 248 CPUs we overflow the 4k buffer of the SCCB,
leading to random data corruption. Basically ALL guest operating systems
call scp read info, so let's limit the machines to 248 CPUs to make it
obvious that >=249 does not work.

As KVM also limits itself to 248 and TCG on s390 does not support
SMP, this should cause no regression for any user as no VMs with more
than 248 VCPUs were ever possible.

Signed-off-by: Christian Borntraeger <address@hidden>
Reviewed-by: David Hildenbrand <address@hidden>
Reviewed-by: Boris Fiuczynski <address@hidden>
Signed-off-by: Cornelia Huck <address@hidden>
 hw/s390x/s390-virtio-ccw.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
index 95ff5e3..e257ca5 100644
--- a/hw/s390x/s390-virtio-ccw.c
+++ b/hw/s390x/s390-virtio-ccw.c
@@ -204,7 +204,7 @@ static void ccw_machine_class_init(ObjectClass *oc, void 
     mc->no_parallel = 1;
     mc->no_sdcard = 1;
     mc->use_sclp = 1;
-    mc->max_cpus = 255;
+    mc->max_cpus = 248;
     mc->get_hotplug_handler = s390_get_hotplug_handler;
     hc->plug = s390_machine_device_plug;
     nc->nmi_monitor_handler = s390_nmi;

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