diff mbox series

[2/5] x86/alternatives: Catch late X86_FEATURE modifiers

Message ID 20240327154317.29909-3-bp@alien8.de (mailing list archive)
State New, archived
Headers show
Series x86/sev: Fix SNP host late disable | expand

Commit Message

Borislav Petkov March 27, 2024, 3:43 p.m. UTC 
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(-)

Comments

Nikolay Borisov March 27, 2024, 3:57 p.m. UTC | #1 
On 27.03.24 г. 17:43 ч., Borislav Petkov wrote:
> 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>

nit: While cleaning this bit mind if you also switch 
alternatives_patched to a bool?
Borislav Petkov April 3, 2024, 5:59 p.m. UTC | #2 
On Wed, Mar 27, 2024 at 05:57:01PM +0200, Nikolay Borisov wrote:
> nit: While cleaning this bit mind if you also switch alternatives_patched to
> a bool?

Busy as hell right now. But I take patches ontop. :-)
diff mbox series

Patch

diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.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);
 
-#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 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, 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 */