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x86/alternatives: Catch late X86_FEATURE modifiers

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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>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Srikanth Aithal <sraithal@amd.com>
Link: https://lore.kernel.org/r/20240327154317.29909-3-bp@alien8.de
This commit is contained in:
Borislav Petkov (AMD) 2024-03-27 16:43:14 +01:00
parent fec50db703
commit ee8962082a
2 changed files with 9 additions and 2 deletions
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8
arch/x86/include/asm/cpufeature.h
View file

@ -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)

3
arch/x86/kernel/cpu/cpuid-deps.c
View file

@ -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 */