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

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 <[email protected]>
Signed-off-by: Borislav Petkov <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Tested-by: Vitezslav Samel <[email protected]>
Tested-by: Ashok Raj <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]

1 files changed, 2 insertions, 4 deletions

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index 10c4fc2c91f8..77e201301528 100644
--- 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;
 	}
 
 	/*