Commit ee896208 authored by Borislav Petkov (AMD)'s avatar Borislav Petkov (AMD)
Browse files

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: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Tested-by: default avatarSrikanth Aithal <sraithal@amd.com>
Link: https://lore.kernel.org/r/20240327154317.29909-3-bp@alien8.de
parent fec50db7

arch/x86/include/asm/cpufeature.h

+6 −2
Original line number Diff line number Diff line
@@ -151,6 +151,10 @@ 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 {			\

							\

	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)

arch/x86/kernel/cpu/cpuid-deps.c

+3 −0
Original line number Diff line number Diff line
@@ -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 */