4.7-stable review patch.  If anyone has any objections, please let me know.


From: Boris Ostrovsky <boris.ostrov...@oracle.com>

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 <boris.ostrov...@oracle.com>
Signed-off-by: David Vrabel <david.vra...@citrix.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

 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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