linux-kernel - [PATCH] x86/microcode/AMD: Document which patches are not released for late loading

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Message-Id: <20230415142821.24725-1-bp@alien8.de>
Date:   Sat, 15 Apr 2023 16:28:21 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     X86 ML <x86@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH] x86/microcode/AMD: Document which patches are not released for late loading

From: "Borislav Petkov (AMD)" <bp@...en8.de>

PeterZ wanted this spelled out explicitly. Add it to the documentation
so that everyone's on the same page wrt to which microcode patches are
not allowed to be late loaded.

Suggested-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
---
 Documentation/x86/microcode.rst | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Documentation/x86/microcode.rst b/Documentation/x86/microcode.rst
index 15b52e2b181d..d5ef9184030c 100644
--- a/Documentation/x86/microcode.rst
+++ b/Documentation/x86/microcode.rst
@@ -218,6 +218,10 @@ a fault happens, the whole core will see it either before the microcode
 patch has been applied or after. In either case, T0 and T1 will have the
 same microcode revision and nothing intermediate.
 
+In addition, microcode patches which modify software-visible features
+like CPUID bits, MSRs, chicken bits, etc are not released for late
+loading.
+
 Builtin microcode
 =================
 
-- 
2.35.1