x86/apic/32: Sanitize logical APIC ID handling

apic::x86_32_early_logical_apicid() is yet another historical joke.

It is used to preset the x86_cpu_to_logical_apicid per CPU variable during
APIC enumeration with:

  - 1 shifted left by the CPU number
  - the physical APIC ID in case of bigsmp

The latter is hillarious because bigsmp uses physical destination mode
which never can use the logical APIC ID.

It gets even worse. As bigsmp can be enforced late in the boot process the
probe function overwrites the per CPU variable which is never used for this
APIC type once again.

Remove that gunk and store 1 << cpunr unconditionally if and only if the
CPU number is less than 8, because the default logical destination mode
only allows up to 8 CPUs.

This is just an intermediate step before removing the per CPU insanity
completely. Stay tuned.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Michael Kelley <mikelley@microsoft.com>
Tested-by: Sohil Mehta <sohil.mehta@intel.com>
Tested-by: Juergen Gross <jgross@suse.com> # Xen PV (dom0 and unpriv. guest)

4 files changed, 2 insertions, 38 deletions

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 6eee777ca73c..89f2a7e5a9f5 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -2435,8 +2435,8 @@ static void cpu_update_apic(int cpu, int apicid)
 	early_per_cpu(x86_cpu_to_apicid, cpu) = apicid;
 #endif
 #ifdef CONFIG_X86_32
-	early_per_cpu(x86_cpu_to_logical_apicid, cpu) =
-		apic->x86_32_early_logical_apicid(cpu);
+	if (cpu < 8)
+		early_per_cpu(x86_cpu_to_logical_apicid, cpu) = 1U << cpu;
 #endif
 	set_cpu_possible(cpu, true);
 	physid_set(apicid, phys_cpu_present_map);
diff --git a/arch/x86/kernel/apic/apic_noop.c b/arch/x86/kernel/apic/apic_noop.c
index c0c3b6bf79b5..ccd74e8016fc 100644
--- a/arch/x86/kernel/apic/apic_noop.c
+++ b/arch/x86/kernel/apic/apic_noop.c
@@ -80,13 +80,6 @@ static void noop_apic_write(u32 reg, u32 val)
 	WARN_ON_ONCE(boot_cpu_has(X86_FEATURE_APIC) && !apic_is_disabled);
 }
 
-#ifdef CONFIG_X86_32
-static int noop_x86_32_early_logical_apicid(int cpu)
-{
-	return BAD_APICID;
-}
-#endif
-
 struct apic apic_noop __ro_after_init = {
 	.name				= "noop",
 	.probe				= noop_probe,
@@ -130,8 +123,4 @@ struct apic apic_noop __ro_after_init = {
 	.icr_write			= noop_apic_icr_write,
 	.wait_icr_idle			= noop_apic_wait_icr_idle,
 	.safe_wait_icr_idle		= noop_safe_apic_wait_icr_idle,
-
-#ifdef CONFIG_X86_32
-	.x86_32_early_logical_apicid	= noop_x86_32_early_logical_apicid,
-#endif
 };
diff --git a/arch/x86/kernel/apic/bigsmp_32.c b/arch/x86/kernel/apic/bigsmp_32.c
index 6f4bd71e97ec..b649048c2019 100644
--- a/arch/x86/kernel/apic/bigsmp_32.c
+++ b/arch/x86/kernel/apic/bigsmp_32.c
@@ -28,12 +28,6 @@ static bool bigsmp_check_apicid_used(physid_mask_t *map, int apicid)
 	return false;
 }
 
-static int bigsmp_early_logical_apicid(int cpu)
-{
-	/* on bigsmp, logical apicid is the same as physical */
-	return early_per_cpu(x86_cpu_to_apicid, cpu);
-}
-
 /*
  * bigsmp enables physical destination mode
  * and doesn't use LDR and DFR
@@ -154,27 +148,15 @@ static struct apic apic_bigsmp __ro_after_init = {
 	.icr_write			= native_apic_icr_write,
 	.wait_icr_idle			= native_apic_wait_icr_idle,
 	.safe_wait_icr_idle		= native_safe_apic_wait_icr_idle,
-
-	.x86_32_early_logical_apicid	= bigsmp_early_logical_apicid,
 };
 
 void __init generic_bigsmp_probe(void)
 {
-	unsigned int cpu;
-
 	if (!probe_bigsmp())
 		return;
 
 	apic = &apic_bigsmp;
 
-	for_each_possible_cpu(cpu) {
-		if (early_per_cpu(x86_cpu_to_logical_apicid,
-				  cpu) == BAD_APICID)
-			continue;
-		early_per_cpu(x86_cpu_to_logical_apicid, cpu) =
-			bigsmp_early_logical_apicid(cpu);
-	}
-
 	pr_info("Overriding APIC driver with %s\n", apic_bigsmp.name);
 }
 
diff --git a/arch/x86/kernel/apic/probe_32.c b/arch/x86/kernel/apic/probe_32.c
index baa8b141eba1..3ee0211b0c29 100644
--- a/arch/x86/kernel/apic/probe_32.c
+++ b/arch/x86/kernel/apic/probe_32.c
@@ -16,11 +16,6 @@
 
 #include "local.h"
 
-static int default_x86_32_early_logical_apicid(int cpu)
-{
-	return 1 << cpu;
-}
-
 static void setup_apic_flat_routing(void)
 {
 #ifdef CONFIG_X86_IO_APIC
@@ -101,8 +96,6 @@ static struct apic apic_default __ro_after_init = {
 	.icr_write			= native_apic_icr_write,
 	.wait_icr_idle			= native_apic_wait_icr_idle,
 	.safe_wait_icr_idle		= native_safe_apic_wait_icr_idle,
-
-	.x86_32_early_logical_apicid	= default_x86_32_early_logical_apicid,
 };
 
 apic_driver(apic_default);