tree e2a4adc45aabc5a1cc0e5529166ab9ca15cd7fee
parent 565fdc6a2afeb14e654a8d9ebc792afb9d2c0019
author Boris Ostrovsky <boris.ostrovsky@oracle.com> 1475687373 -0400
committer David Vrabel <david.vrabel@citrix.com> 1475750825 +0100

xen/x86: Update topology map for PV VCPUs

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.ostrovsky@oracle.com>
Cc: stable@vger.kernel.org
Signed-off-by: David Vrabel <david.vrabel@citrix.com>