Commit c90399fb authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Borislav Petkov (AMD)
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x86/cpu: Ensure that CPU info updates are propagated on UP 



The boot sequence evaluates CPUID information twice:

  1) During early boot

  2) When finalizing the early setup right before
     mitigations are selected and alternatives are patched.

In both cases the evaluation is stored in boot_cpu_data, but on UP the
copying of boot_cpu_data to the per CPU info of the boot CPU happens
between #1 and #2. So any update which happens in #2 is never propagated to
the per CPU info instance.

Consolidate the whole logic and copy boot_cpu_data right before applying
alternatives as that's the point where boot_cpu_data is in it's final
state and not supposed to change anymore.

This also removes the voodoo mb() from smp_prepare_cpus_common() which
had absolutely no purpose.

Fixes: 71eb4893 ("x86/percpu: Cure per CPU madness on UP")
Reported-by: default avatarGuenter Roeck <linux@roeck-us.net>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Tested-by: default avatarGuenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20240322185305.127642785@linutronix.de
parent 4e51653d

arch/x86/kernel/cpu/common.c

+9 −0
Original line number Diff line number Diff line
@@ -2307,6 +2307,8 @@ void arch_smt_update(void) 


void __init arch_cpu_finalize_init(void)

{

	struct cpuinfo_x86 *c = this_cpu_ptr(&cpu_info);



	identify_boot_cpu();



	select_idle_routine();
@@ -2345,6 +2347,13 @@ void __init arch_cpu_finalize_init(void) 
	fpu__init_system();

	fpu__init_cpu();



	/*

	 * Ensure that access to the per CPU representation has the initial

	 * boot CPU configuration.

	 */

	*c = boot_cpu_data;

	c->initialized = true;



	alternative_instructions();



	if (IS_ENABLED(CONFIG_X86_64)) {

arch/x86/kernel/setup.c

+0 −10
Original line number Diff line number Diff line
@@ -1206,16 +1206,6 @@ void __init i386_reserve_resources(void) 


#endif /* CONFIG_X86_32 */



#ifndef CONFIG_SMP

void __init smp_prepare_boot_cpu(void)

{

	struct cpuinfo_x86 *c = &cpu_data(0);



	*c = boot_cpu_data;

	c->initialized = true;

}

#endif



static struct notifier_block kernel_offset_notifier = {

	.notifier_call = dump_kernel_offset

};

arch/x86/kernel/smpboot.c

+5 −27
Original line number Diff line number Diff line
@@ -313,14 +313,6 @@ static void notrace start_secondary(void *unused) 
	cpu_startup_entry(CPUHP_AP_ONLINE_IDLE);

}



static void __init smp_store_boot_cpu_info(void)

{

	struct cpuinfo_x86 *c = &cpu_data(0);



	*c = boot_cpu_data;

	c->initialized = true;

}



/*

 * The bootstrap kernel entry code has set these up. Save them for

 * a given CPU
@@ -1039,29 +1031,15 @@ static __init void disable_smp(void) 
	cpumask_set_cpu(0, topology_die_cpumask(0));

}



static void __init smp_cpu_index_default(void)

{

	int i;

	struct cpuinfo_x86 *c;



	for_each_possible_cpu(i) {

		c = &cpu_data(i);

		/* mark all to hotplug */

		c->cpu_index = nr_cpu_ids;

	}

}



void __init smp_prepare_cpus_common(void)

{

	unsigned int i;



	smp_cpu_index_default();



	/*

	 * Setup boot CPU information

	 */

	smp_store_boot_cpu_info(); /* Final full version of the data */

	mb();

	/* Mark all except the boot CPU as hotpluggable */

	for_each_possible_cpu(i) {

		if (i)

			per_cpu(cpu_info.cpu_index, i) = nr_cpu_ids;

	}



	for_each_possible_cpu(i) {

		zalloc_cpumask_var(&per_cpu(cpu_sibling_map, i), GFP_KERNEL);