[PATCH] xen/x86: Update topology map for PV VCPUs

From: Boris Ostrovsky
Date: Wed Oct 05 2016 - 13:15:06 EST

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@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx

Copying Andrew for the CPUID part.

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

diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
index 311acad..9fa27ce 100644
--- 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);