linux-kernel - [tip: x86/alternatives] x86/alternatives: Catch late X86

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Message-ID: <171268269269.10875.17747775043118568657.tip-bot2@tip-bot2>
Date: Tue, 09 Apr 2024 17:11:32 -0000
From: "tip-bot2 for Borislav Petkov (AMD)" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: "Borislav Petkov (AMD)" <bp@...en8.de>, Ingo Molnar <mingo@...nel.org>,
 Srikanth Aithal <sraithal@....com>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject:
 [tip: x86/alternatives] x86/alternatives: Catch late X86_FEATURE modifiers

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

Commit-ID:     ee8962082a4413dba1a1b3d3d23490c5221f3b8a
Gitweb:        https://git.kernel.org/tip/ee8962082a4413dba1a1b3d3d23490c5221f3b8a
Author:        Borislav Petkov (AMD) <bp@...en8.de>
AuthorDate:    Wed, 27 Mar 2024 16:43:14 +01:00
Committer:     Borislav Petkov (AMD) <bp@...en8.de>
CommitterDate: Tue, 09 Apr 2024 18:03:53 +02:00

x86/alternatives: Catch late X86_FEATURE modifiers

After alternatives have been patched, changes to the X86_FEATURE flags
won't take effect and could potentially even be wrong.

Warn about it.

This is something which has been long overdue.

Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Tested-by: Srikanth Aithal <sraithal@....com>
Link: https://lore.kernel.org/r/20240327154317.29909-3-bp@alien8.de
---
 arch/x86/include/asm/cpufeature.h | 8 ++++++--
 arch/x86/kernel/cpu/cpuid-deps.c  | 3 +++
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index 686e92d..f07687d 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -150,8 +150,12 @@ extern const char * const x86_bug_flags[NBUGINTS*32];
 extern void setup_clear_cpu_cap(unsigned int bit);
 extern void clear_cpu_cap(struct cpuinfo_x86 *c, unsigned int bit);
 
-#define setup_force_cpu_cap(bit) do { \
-	set_cpu_cap(&boot_cpu_data, bit);	\
+#define setup_force_cpu_cap(bit) do {			\
+							\
+	if (!boot_cpu_has(bit))				\
+		WARN_ON(alternatives_patched);		\
+							\
+	set_cpu_cap(&boot_cpu_data, bit);		\
 	set_bit(bit, (unsigned long *)cpu_caps_set);	\
 } while (0)
 
diff --git a/arch/x86/kernel/cpu/cpuid-deps.c b/arch/x86/kernel/cpu/cpuid-deps.c
index b717420..5dd427c 100644
--- a/arch/x86/kernel/cpu/cpuid-deps.c
+++ b/arch/x86/kernel/cpu/cpuid-deps.c
@@ -114,6 +114,9 @@ static void do_clear_cpu_cap(struct cpuinfo_x86 *c, unsigned int feature)
 	if (WARN_ON(feature >= MAX_FEATURE_BITS))
 		return;
 
+	if (boot_cpu_has(feature))
+		WARN_ON(alternatives_patched);
+
 	clear_feature(c, feature);
 
 	/* Collect all features to disable, handling dependencies */