Received-SPF: pass (google.com: domain of linux-kernel+bounces-121556-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:4601:e00::3 as permitted sender) client-ip=2604:1380:4601:e00::3;
From: Borislav Petkov <bp@alien8.de>
To: X86 ML <x86@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
	KVM <kvm@vger.kernel.org>,
	Ashish Kalra <ashish.kalra@amd.com>,
	Joerg Roedel <joro@8bytes.org>,
	Michael Roth <michael.roth@amd.com>,
	Tom Lendacky <thomas.lendacky@amd.com>
Subject: [PATCH 2/5] x86/alternatives: Catch late X86_FEATURE modifiers
Date: Wed, 27 Mar 2024 16:43:14 +0100
Message-ID: <20240327154317.29909-3-bp@alien8.de>
In-Reply-To: <20240327154317.29909-1-bp@alien8.de>
References: <20240327154317.29909-1-bp@alien8.de>
Precedence: bulk
MIME-Version: 1.0
Content-Transfer-Encoding: quoted-printable

From: "Borislav Petkov (AMD)" <bp@alien8.de>

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@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/cpu=
feature.h
index 1ef620d508f4..d0b9c411144b 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -146,8 +146,12 @@ 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);
=20
-#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)
=20
diff --git a/arch/x86/kernel/cpu/cpuid-deps.c b/arch/x86/kernel/cpu/cpuid=
-deps.c
index b7174209d855..5dd427c6feb2 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, u=
nsigned int feature)
 	if (WARN_ON(feature >=3D MAX_FEATURE_BITS))
 		return;
=20
+	if (boot_cpu_has(feature))
+		WARN_ON(alternatives_patched);
+
 	clear_feature(c, feature);
=20
 	/* Collect all features to disable, handling dependencies */
--=20
2.43.0