[tip: x86/microcode] x86/microcode/AMD: Document which patches are not released for late loading

[tip-bot2 for Borislav Petkov (AMD)]

The following commit has been merged into the x86/microcode branch of tip:

Commit-ID:     07cc5639f14dcc3763a926dbe7cc38ac2694de0c
Gitweb:        https://git.kernel.org/tip/07cc5639f14dcc3763a926dbe7cc38ac2694de0c
Author:        Borislav Petkov (AMD) <bp@xxxxxxxxx>
AuthorDate:    Sat, 15 Apr 2023 16:23:29 +02:00
Committer:     Borislav Petkov (AMD) <bp@xxxxxxxxx>
CommitterDate: Mon, 17 Apr 2023 15:38:33 +02:00

x86/microcode/AMD: Document which patches are not released for late loading

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@xxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Link: https://lore.kernel.org/r/20230415142821.24725-1-bp@xxxxxxxxx
---
 Documentation/x86/microcode.rst | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Documentation/x86/microcode.rst b/Documentation/x86/microcode.rst
index 15b52e2..d5ef918 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
 =================