x86/microcode: Do not exit early from __reload_late()

BugLink: http://bugs.launchpad.net/bugs/1778265
commit 09e182d17e8891dd73baba961a0f5a82e9274c97 upstream.

Vitezslav reported a case where the

  "Timeout during microcode update!"

panic would hit. After a deeper look, it turned out that his .config had
CONFIG_HOTPLUG_CPU disabled which practically made save_mc_for_early() a
no-op.

When that happened, the discovered microcode patch wasn't saved into the
cache and the late loading path wouldn't find any.

This, then, lead to early exit from __reload_late() and thus CPUs waiting
until the timeout is reached, leading to the panic.

In hindsight, that function should have been written so it does not return
before the post-synchronization. Oh well, I know better now...

Fixes: bb8c13d61a62 ("x86/microcode: Fix CPU synchronization routine")
Reported-by: Vitezslav Samel <vitezslav@samel.cz>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Vitezslav Samel <vitezslav@samel.cz>
Tested-by: Ashok Raj <ashok.raj@intel.com>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/20180418081140.GA2439@pc11.op.pod.cz
Link: https://lkml.kernel.org/r/20180421081930.15741-2-bp@alien8.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 10c4fc2c91f8ed1dd6879c8b0b8aa24d7275cd3b..77e201301528817e32537194cf5e075b29aa9686 100644 (file)
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -564,14 +564,12 @@ static int __reload_late(void *info)
        apply_microcode_local(&err);
        spin_unlock(&update_lock);
 
+       /* siblings return UCODE_OK because their engine got updated already */
        if (err > UCODE_NFOUND) {
                pr_warn("Error reloading microcode on CPU %d\n", cpu);
-               return -1;
-       /* siblings return UCODE_OK because their engine got updated already */
+               ret = -1;
        } else if (err == UCODE_UPDATED || err == UCODE_OK) {
                ret = 1;
-       } else {
-               return ret;
        }
 
        /*