Re: [PATCH] xen/x86: Update topology map for PV VCPUs
From: Andrew Cooper
Date: Wed Oct 05 2016 - 13:41:54 EST
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
I am currently working on fixing the reported topology information to be
architecturally plausible, but current and previous hypervisors will be
> 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);