x86/MCE/AMD: Allow thresholding interface updates after init

Changes to the AMD Thresholding sysfs code prevents sysfs writes from
updating the underlying registers once CPU init is completed, i.e.
"threshold_banks" is set.

Allow the registers to be updated if the thresholding interface is
already initialized or if in the init path. Use the "set_lvt_off" value
to indicate if running in the init path, since this value is only set
during init.

Fixes: a037f3c ("x86/mce/amd: Make threshold bank setting hotplug robust")
Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20220117161328.19148-1-yazen.ghannam@amd.com

arch/x86/kernel/cpu/mce/amd.c

@@ -423,7 +423,7 @@ static void threshold_restart_bank(void *_tr)
 	u32 hi, lo;
 
 	/* sysfs write might race against an offline operation */
-	if (this_cpu_read(threshold_banks))
+	if (!this_cpu_read(threshold_banks) && !tr->set_lvt_off)
 		return;
 
 	rdmsr(tr->b->address, lo, hi);