On 05/10/16 18:09, Boris Ostrovsky wrote: > 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. Yeah - that leaf is usually fiction. (Specifically, the fiction of whichever cpu a specific toolstack function happened to sample at the point in time that it was choosing which cpuid values to fake up for the guest). I am currently working on fixing the reported topology information to be architecturally plausible, but current and previous hypervisors will be wrong. ~Andrew > > 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; > set_cpu_sibling_map(cpu); > > + /* > + * 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); > + > xen_setup_cpu_clockevents(); > > notify_cpu_starting(cpu); -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html