x86/apic: Remove yet another dubious callback

Paranoia is not wrong, but having an APIC callback which is in most
implementations a complete NOOP and in one actually looking whether the
APICID of an upcoming CPU has been registered. The same APICID which was
used to bring the CPU out of wait for startup.

That's paranoia for the paranoia sake. Remove the voodoo.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Michael Kelley <mhklinux@outlook.com>
Tested-by: Sohil Mehta <sohil.mehta@intel.com>
Link: https://lore.kernel.org/r/20240212154640.116510935@linutronix.de

arch/x86/include/asm/apic.h

@@ -288,7 +288,6 @@ struct apic {
 	/* Probe, setup and smpboot functions */
 	int	(*probe)(void);
 	int	(*acpi_madt_oem_check)(char *oem_id, char *oem_table_id);
-	bool	(*apic_id_registered)(void);
 
 	void	(*init_apic_ldr)(void);
 	u32	(*cpu_present_to_apicid)(int mps_cpu);

arch/x86/kernel/apic/apic.c

@@ -1538,9 +1538,6 @@ static void setup_local_APIC(void)
 		apic_write(APIC_ESR, 0);
 	}
 #endif
-	/* Validate that the APIC is registered if required */
-	BUG_ON(apic->apic_id_registered && !apic->apic_id_registered());
-
 	/*
 	 * Intel recommends to set DFR, LDR and TPR before enabling
 	 * an APIC.  See e.g. "AP-388 82489DX User's Manual" (Intel

arch/x86/kernel/apic/apic_common.c

@@ -27,11 +27,6 @@ u32 default_cpu_present_to_apicid(int mps_cpu)
 }
 EXPORT_SYMBOL_GPL(default_cpu_present_to_apicid);
 
-bool default_apic_id_registered(void)
-{
-	return test_bit(read_apic_id(), phys_cpu_present_map);
-}
-
 /*
  * Set up the logical destination ID when the APIC operates in logical
  * destination mode.

arch/x86/kernel/apic/apic_flat_64.c

@@ -70,7 +70,6 @@ static struct apic apic_flat __ro_after_init = {
 	.name				= "flat",
 	.probe				= flat_probe,
 	.acpi_madt_oem_check		= flat_acpi_madt_oem_check,
-	.apic_id_registered		= default_apic_id_registered,
 
 	.dest_mode_logical		= true,
 
@@ -139,7 +138,6 @@ static struct apic apic_physflat __ro_after_init = {
 	.name				= "physical flat",
 	.probe				= physflat_probe,
 	.acpi_madt_oem_check		= physflat_acpi_madt_oem_check,
-	.apic_id_registered		= default_apic_id_registered,
 
 	.dest_mode_logical		= false,
 

arch/x86/kernel/apic/local.h

@@ -61,8 +61,6 @@ void default_send_IPI_allbutself(int vector);
 void default_send_IPI_all(int vector);
 void default_send_IPI_self(int vector);
 
-bool default_apic_id_registered(void);
-
 #ifdef CONFIG_X86_32
 void default_send_IPI_mask_sequence_logical(const struct cpumask *mask, int vector);
 void default_send_IPI_mask_allbutself_logical(const struct cpumask *mask, int vector);

arch/x86/kernel/apic/probe_32.c

@@ -38,7 +38,6 @@ static struct apic apic_default __ro_after_init = {
 
 	.name				= "default",
 	.probe				= probe_default,
-	.apic_id_registered		= default_apic_id_registered,
 
 	.dest_mode_logical		= true,