linux-kernel - [PATCH] x86, microcode: Limit the microcode reloading to 64-bit for now

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Date:	Sun, 30 Nov 2014 14:26:39 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	X86 ML <x86@...nel.org>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] x86, microcode: Limit the microcode reloading to 64-bit for now

From: Borislav Petkov <bp@...e.de>

First, there was this: https://bugzilla.kernel.org/show_bug.cgi?id=88001

The problem there was that microcode patches are not being reapplied
after suspend-to-ram. It was important to reapply them, though, because
of for example Haswell's TSX erratum which disabled TSX instructions
with a microcode patch.

A simple fix was

fb86b97300d9 ("x86, microcode: Update BSPs microcode on resume")

but, as it is often the case, simple fixes are too simple. This one
causes 32-bit resume to fail:

https://bugzilla.kernel.org/show_bug.cgi?id=88391

Properly fixing this would require more involved changes for which it is
too late now, before the merge window. Thus, limit this to 64-bit only
temporarily.

Signed-off-by: Borislav Petkov <bp@...e.de>
---
 arch/x86/kernel/cpu/microcode/core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index 2ce9051174e6..08fe6e8a726e 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -465,6 +465,7 @@ static void mc_bp_resume(void)
 
 	if (uci->valid && uci->mc)
 		microcode_ops->apply_microcode(cpu);
+#ifdef CONFIG_X86_64
 	else if (!uci->mc)
 		/*
 		 * We might resume and not have applied late microcode but still
@@ -473,6 +474,7 @@ static void mc_bp_resume(void)
 		 * applying patches early on the APs.
 		 */
 		load_ucode_ap();
+#endif
 }
 
 static struct syscore_ops mc_syscore_ops = {
-- 
2.0.0

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