x86/microcode: Fix the microcode load on CPU hotplug for real

BugLink: https://bugs.launchpad.net/bugs/1838824
commit 5423f5ce5ca410b3646f355279e4e937d452e622 upstream.

A recent change moved the microcode loader hotplug callback into the early
startup phase which is running with interrupts disabled. It missed that
the callbacks invoke sysfs functions which might sleep causing nice 'might
sleep' splats with proper debugging enabled.

Split the callbacks and only load the microcode in the early startup phase
and move the sysfs handling back into the later threaded and preemptible
bringup phase where it was before.

Fixes: 78f4e932f776 ("x86/microcode, cpuhotplug: Add a microcode loader CPU hotplug callback")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: stable@vger.kernel.org
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1906182228350.1766@nanos.tec.linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index b7027e667604e9947c39b1fade154589612030cb..a96091d44a459b57925cab12256646949b1b2243 100644 (file)
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -790,13 +790,16 @@ static struct syscore_ops mc_syscore_ops = {
        .resume                 = mc_bp_resume,
 };
 
-static int mc_cpu_online(unsigned int cpu)
+static int mc_cpu_starting(unsigned int cpu)
 {
-       struct device *dev;
-
-       dev = get_cpu_device(cpu);
        microcode_update_cpu(cpu);
        pr_debug("CPU%d added\n", cpu);
+       return 0;
+}
+
+static int mc_cpu_online(unsigned int cpu)
+{
+       struct device *dev = get_cpu_device(cpu);
 
        if (sysfs_create_group(&dev->kobj, &mc_attr_group))
                pr_err("Failed to create group for CPU%d\n", cpu);
@@ -873,7 +876,9 @@ int __init microcode_init(void)
                goto out_ucode_group;
 
        register_syscore_ops(&mc_syscore_ops);
-       cpuhp_setup_state_nocalls(CPUHP_AP_MICROCODE_LOADER, "x86/microcode:online",
+       cpuhp_setup_state_nocalls(CPUHP_AP_MICROCODE_LOADER, "x86/microcode:starting",
+                                 mc_cpu_starting, NULL);
+       cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "x86/microcode:online",
                                  mc_cpu_online, mc_cpu_down_prep);
 
        pr_info("Microcode Update Driver: v%s.", DRIVER_VERSION);