[Xen-devel] [PATCH] x86: fix cpu_sibling_map initialization when topology CPUID leaf is present

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

c/s 21811:12f0618400de broke this by not properly initializing struct
cpuinfo_x86's x86_num_siblings member (other than Linux, where this is
a global variable, it is being maintained per CPU by Xen).

Hyper-threaded CPUs with CPUID leaf 0xb present had therefore all
cpu_sibling_map-s with just a single bit set, thus improperly feeding
the scheduler.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>

--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -477,7 +477,7 @@ void __cpuinit detect_extended_topology(
 {
        unsigned int eax, ebx, ecx, edx, sub_index;
        unsigned int ht_mask_width, core_plus_mask_width;
-       unsigned int core_select_mask, core_level_siblings, smp_num_siblings;
+       unsigned int core_select_mask, core_level_siblings;
        unsigned int initial_apicid;
        int cpu = smp_processor_id();
 
@@ -495,7 +495,7 @@ void __cpuinit detect_extended_topology(
        initial_apicid = edx;
 
        /* Populate HT related information from sub-leaf level 0 */
-       core_level_siblings = smp_num_siblings = LEVEL_MAX_SIBLINGS(ebx);
+       core_level_siblings = c->x86_num_siblings = LEVEL_MAX_SIBLINGS(ebx);
        core_plus_mask_width = ht_mask_width = BITS_SHIFT_NEXT_LEVEL(eax);
 
        sub_index = 1;
@@ -519,7 +519,7 @@ void __cpuinit detect_extended_topology(
        phys_proc_id[cpu] = phys_pkg_id(initial_apicid, core_plus_mask_width);
 
        c->apicid = phys_pkg_id(initial_apicid, 0);
-       c->x86_max_cores = (core_level_siblings / smp_num_siblings);
+       c->x86_max_cores = (core_level_siblings / c->x86_num_siblings);
 
        if ( opt_cpu_info )
        {

Attachment: x86-topology.patch
Description: Text document

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