Merge tag 'x86-urgent-2023-12-23' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 fixes from Ingo Molnar:

 - Fix a secondary CPUs enumeration regression caused by creative MADT
   APIC table entries on certain systems.

 - Fix a race in the NOP-patcher that can spuriously trigger crashes on
   bootup.

 - Fix a bootup failure regression caused by the parallel bringup code,
   caused by firmware inconsistency between the APIC initialization
   states of the boot and secondary CPUs, on certain systems.

* tag 'x86-urgent-2023-12-23' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/acpi: Handle bogus MADT APIC tables gracefully
  x86/alternatives: Disable interrupts and sync when optimizing NOPs in place
  x86/alternatives: Sync core before enabling interrupts
  x86/smpboot/64: Handle X2APIC BIOS inconsistency gracefully

arch/x86/kernel/acpi/boot.c

@@ -293,6 +293,7 @@ acpi_parse_lapic(union acpi_subtable_headers * header, const unsigned long end)
 			    processor->processor_id, /* ACPI ID */
 			    processor->lapic_flags & ACPI_MADT_ENABLED);
 
+	has_lapic_cpus = true;
 	return 0;
 }
 
@@ -1134,7 +1135,6 @@ static int __init acpi_parse_madt_lapic_entries(void)
 	if (!count) {
 		count = acpi_table_parse_madt(ACPI_MADT_TYPE_LOCAL_APIC,
 					acpi_parse_lapic, MAX_LOCAL_APIC);
-		has_lapic_cpus = count > 0;
 		x2count = acpi_table_parse_madt(ACPI_MADT_TYPE_LOCAL_X2APIC,
 					acpi_parse_x2apic, MAX_LOCAL_APIC);
 	}

arch/x86/kernel/alternative.c

@@ -255,6 +255,16 @@ static void __init_or_module noinline optimize_nops(u8 *instr, size_t len)
 	}
 }
 
+static void __init_or_module noinline optimize_nops_inplace(u8 *instr, size_t len)
+{
+	unsigned long flags;
+
+	local_irq_save(flags);
+	optimize_nops(instr, len);
+	sync_core();
+	local_irq_restore(flags);
+}
+
 /*
  * In this context, "source" is where the instructions are placed in the
  * section .altinstr_replacement, for example during kernel build by the
@@ -438,7 +448,7 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
 		 *   patch if feature is *NOT* present.
 		 */
 		if (!boot_cpu_has(a->cpuid) == !(a->flags & ALT_FLAG_NOT)) {
-			optimize_nops(instr, a->instrlen);
+			optimize_nops_inplace(instr, a->instrlen);
 			continue;
 		}
 
@@ -1685,8 +1695,8 @@ void __init_or_module text_poke_early(void *addr, const void *opcode,
 	} else {
 		local_irq_save(flags);
 		memcpy(addr, opcode, len);
-		local_irq_restore(flags);
 		sync_core();
+		local_irq_restore(flags);
 
 		/*
 		 * Could also do a CLFLUSH here to speed up CPU recovery; but

arch/x86/kernel/head_64.S

@@ -255,6 +255,22 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL)
 	testl	$X2APIC_ENABLE, %eax
 	jnz	.Lread_apicid_msr
 
+#ifdef CONFIG_X86_X2APIC
+	/*
+	 * If system is in X2APIC mode then MMIO base might not be
+	 * mapped causing the MMIO read below to fault. Faults can't
+	 * be handled at that point.
+	 */
+	cmpl	$0, x2apic_mode(%rip)
+	jz	.Lread_apicid_mmio
+
+	/* Force the AP into X2APIC mode. */
+	orl	$X2APIC_ENABLE, %eax
+	wrmsr
+	jmp	.Lread_apicid_msr
+#endif
+
+.Lread_apicid_mmio:
 	/* Read the APIC ID from the fix-mapped MMIO space. */
 	movq	apic_mmio_base(%rip), %rcx
 	addq	$APIC_ID, %rcx