[PATCH] x86, amd: Re-enable CPU topology extensions in case BIOS hasdisabled it

From: Andreas Herrmann
Date: Tue Apr 03 2012 - 06:13:07 EST

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@xxxxxxx>
arch/x86/kernel/cpu/amd.c | 18 ++++++++++++++++++
1 files changed, 18 insertions(+), 0 deletions(-)

Hi Ingo,

Hope this new commit messages answers your questions.

Of course this patch is more a workaround for "suboptimal BIOS
settings" and thus not strictly stable material. (BTW, no there is no
way to change the BIOS setting here.) But as a whole bunch of systems
will be affected it might also be reasonable to add this patch to
stable Linux versions.


diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 1248f9c..0ae388d 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -579,6 +579,24 @@ 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");
+ }
+ }
+ }

/* Multi core CPU? */

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/