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Subject[PATCH 4.7 12/31] xen/x86: Update topology map for PV VCPUs
4.7-stable review patch.  If anyone has any objections, please let me know.


From: Boris Ostrovsky <>

commit a6a198bc60e6c980a56eca24d33dc7f29139f8ea upstream.

Early during boot topology_update_package_map() computes
logical_pkg_ids for all present processors.

Later, when processors are brought up, identify_cpu() updates
these values based on phys_pkg_id which is a function of
initial_apicid. On PV guests the latter may point to a
non-existing node, causing logical_pkg_ids to be set to -1.

Intel's RAPL uses logical_pkg_id (as topology_logical_package_id())
to index its arrays and therefore in this case will point to index
65535 (since logical_pkg_id is a u16). This could lead to either a
crash or may actually access random memory location.

As a workaround, we recompute topology during CPU bringup to reset
logical_pkg_id to a valid value.

(The reason for initial_apicid being bogus is because it is
initial_apicid of the processor from which the guest is launched.
This value is CPUID(1).EBX[31:24])

Signed-off-by: Boris Ostrovsky <>
Signed-off-by: David Vrabel <>
Signed-off-by: Greg Kroah-Hartman <>

arch/x86/xen/smp.c | 6 ++++++
1 file changed, 6 insertions(+)

--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -87,6 +87,12 @@ static void cpu_bringup(void)
cpu_data(cpu).x86_max_cores = 1;

+ /*
+ * identify_cpu() may have set logical_pkg_id to -1 due
+ * to incorrect phys_proc_id. Let's re-comupte it.
+ */
+ topology_update_package_map(apic->cpu_present_to_apicid(cpu), cpu);


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