[PATCH 2/2] x86/microcode: Do not exit early from __reload_late()

From: Borislav Petkov
Date: Fri Apr 20 2018 - 06:37:19 EST


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 our
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, I should've made that function not return before the
post-synchronization. Oh well, I know better now...

Reported-by: Vitezslav Samel <vitezslav@xxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Cc: Ashok Raj <ashok.raj@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Fixes: bb8c13d61a62 ("x86/microcode: Fix CPU synchronization routine")
Link: http://lkml.kernel.org/r/20180418081140.GA2439@xxxxxxxxxxxxxx
---
arch/x86/kernel/cpu/microcode/core.c | 6 ++----
1 file 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;
}

/*
--
2.13.0

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