x86, microcode: Don't request microcode from userspace unnecessarily
Requesting the microcode from userspace *every time* when onlining CPUs
(during a CPU hotplug operation) is unnecessary. Thus, ensure that
once the kernel gets the microcode after booting, it is not freed nor
invalidated when a CPU goes offline, so that it can be reused when that
CPU comes back online, without requesting userspace for it again. As a
result, the CPU hotplug operations become faster as well.
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Acked-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Andreas Herrmann <andreas.herrmann3@amd.com>
Link: http://lkml.kernel.org/r/4E91F908.5010006@linux.vnet.ibm.com
Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
diff --git a/arch/x86/kernel/microcode_core.c b/arch/x86/kernel/microcode_core.c
index f924280..f2d2a66 100644
--- a/arch/x86/kernel/microcode_core.c
+++ b/arch/x86/kernel/microcode_core.c
@@ -483,7 +483,13 @@
sysfs_remove_group(&sys_dev->kobj, &mc_attr_group);
pr_debug("CPU%d removed\n", cpu);
break;
- case CPU_DEAD:
+
+ /*
+ * When a CPU goes offline, don't free up or invalidate the copy of
+ * the microcode in kernel memory, so that we can reuse it when the
+ * CPU comes back online without unnecessarily requesting the userspace
+ * for it again.
+ */
case CPU_UP_CANCELED_FROZEN:
/* The CPU refused to come up during a system resume */
microcode_fini_cpu(cpu);