x86/amd: Re-enable CPU topology extensions in case BIOS has disabled it

BIOS will switch off the corresponding feature flag on family
15h models 10h-1fh non-desktop CPUs.

The topology extension CPUID leafs are required to detect which
cores belong to the same compute unit. (thread siblings mask is
set accordingly and also correct information about L1i and L2
cache sharing depends on this).

W/o this patch we wouldn't see which cores belong to the same
compute unit and also cache sharing information for L1i and L2
would be incorrect on such systems.

Signed-off-by: Andreas Herrmann <andreas.herrmann3@amd.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 18 insertions, 0 deletions

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 1c67ca100e4c..146bb6218eec 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -580,6 +580,24 @@ static void __cpuinit init_amd(struct cpuinfo_x86 *c)
                 }
         }
 
+        /* re-enable TopologyExtensions if switched off by BIOS */
+        if ((c->x86 == 0x15) &&
+            (c->x86_model >= 0x10) && (c->x86_model <= 0x1f) &&
+            !cpu_has(c, X86_FEATURE_TOPOEXT)) {
+                u64 val;
+
+                if (!rdmsrl_amd_safe(0xc0011005, &val)) {
+                        val |= 1ULL << 54;
+                        wrmsrl_amd_safe(0xc0011005, val);
+                        rdmsrl(0xc0011005, val);
+                        if (val & (1ULL << 54)) {
+                                set_cpu_cap(c, X86_FEATURE_TOPOEXT);
+                                printk(KERN_INFO FW_INFO "CPU: Re-enabling "
+                                  "disabled Topology Extensions Support\n");
+                        }
+                }
+        }
+
         cpu_detect_cache_sizes(c);
 
         /* Multi core CPU? */