x86/idt: Consolidate idt functionality

- Move load_current_idt() out of line and replace the hideous comment with
   a lockdep assert. This allows to make idt_table and idt_descr static.

 - Mark idt_table read only after the IDT initialization is complete.

 - Shuffle code around to consolidate the #ifdef sections into one.

 - Adapt the F00F bug code.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200528145523.084915381@linutronix.de

arch/x86/include/asm/desc.h

@@ -40,9 +40,6 @@ static inline void fill_ldt(struct desc_struct *desc, const struct user_desc *in
 	desc->l			= 0;
 }
 
-extern struct desc_ptr idt_descr;
-extern gate_desc idt_table[];
-
 struct gdt_page {
 	struct desc_struct gdt[GDT_ENTRIES];
 } __attribute__((aligned(PAGE_SIZE)));
@@ -388,22 +385,12 @@ void alloc_intr_gate(unsigned int n, const void *addr);
 
 extern unsigned long system_vectors[];
 
-/*
- * The load_current_idt() must be called with interrupts disabled
- * to avoid races. That way the IDT will always be set back to the expected
- * descriptor. It's also called when a CPU is being initialized, and
- * that doesn't need to disable interrupts, as nothing should be
- * bothering the CPU then.
- */
-static __always_inline void load_current_idt(void)
-{
-	load_idt((const struct desc_ptr *)&idt_descr);
-}
-
+extern void load_current_idt(void);
 extern void idt_setup_early_handler(void);
 extern void idt_setup_early_traps(void);
 extern void idt_setup_traps(void);
 extern void idt_setup_apic_and_irq_gates(void);
+extern bool idt_is_f00f_address(unsigned long address);
 
 #ifdef CONFIG_X86_64
 extern void idt_setup_early_pf(void);

arch/x86/kernel/idt.c

@@ -5,6 +5,7 @@
 #include <linux/interrupt.h>
 
 #include <asm/cpu_entry_area.h>
+#include <asm/set_memory.h>
 #include <asm/traps.h>
 #include <asm/proto.h>
 #include <asm/desc.h>
@@ -156,37 +157,25 @@ static const __initconst struct idt_data apic_idts[] = {
 #endif
 };
 
-#ifdef CONFIG_X86_64
-/*
- * Early traps running on the DEFAULT_STACK because the other interrupt
- * stacks work only after cpu_init().
- */
-static const __initconst struct idt_data early_pf_idts[] = {
-	INTG(X86_TRAP_PF,		asm_exc_page_fault),
-};
-#endif
-
-/* Must be page-aligned because the real IDT is used in a fixmap. */
-gate_desc idt_table[IDT_ENTRIES] __page_aligned_bss;
+/* Must be page-aligned because the real IDT is used in the cpu entry area */
+static gate_desc idt_table[IDT_ENTRIES] __page_aligned_bss;
 
 struct desc_ptr idt_descr __ro_after_init = {
 	.size		= IDT_TABLE_SIZE - 1,
 	.address	= (unsigned long) idt_table,
 };
 
-#ifdef CONFIG_X86_64
-/*
- * The exceptions which use Interrupt stacks. They are setup after
- * cpu_init() when the TSS has been initialized.
- */
-static const __initconst struct idt_data ist_idts[] = {
-	ISTG(X86_TRAP_DB,	asm_exc_debug,		IST_INDEX_DB),
-	ISTG(X86_TRAP_NMI,	asm_exc_nmi,		IST_INDEX_NMI),
-	ISTG(X86_TRAP_DF,	asm_exc_double_fault,	IST_INDEX_DF),
-#ifdef CONFIG_X86_MCE
-	ISTG(X86_TRAP_MC,	asm_exc_machine_check,	IST_INDEX_MCE),
-#endif
-};
+void load_current_idt(void)
+{
+	lockdep_assert_irqs_disabled();
+	load_idt(&idt_descr);
+}
+
+#ifdef CONFIG_X86_F00F_BUG
+bool idt_is_f00f_address(unsigned long address)
+{
+	return ((address - idt_descr.address) >> 3) == 6;
+}
 #endif
 
 static inline void idt_init_desc(gate_desc *gate, const struct idt_data *d)
@@ -255,6 +244,27 @@ void __init idt_setup_traps(void)
 }
 
 #ifdef CONFIG_X86_64
+/*
+ * Early traps running on the DEFAULT_STACK because the other interrupt
+ * stacks work only after cpu_init().
+ */
+static const __initconst struct idt_data early_pf_idts[] = {
+	INTG(X86_TRAP_PF,		asm_exc_page_fault),
+};
+
+/*
+ * The exceptions which use Interrupt stacks. They are setup after
+ * cpu_init() when the TSS has been initialized.
+ */
+static const __initconst struct idt_data ist_idts[] = {
+	ISTG(X86_TRAP_DB,	asm_exc_debug,		IST_INDEX_DB),
+	ISTG(X86_TRAP_NMI,	asm_exc_nmi,		IST_INDEX_NMI),
+	ISTG(X86_TRAP_DF,	asm_exc_double_fault,	IST_INDEX_DF),
+#ifdef CONFIG_X86_MCE
+	ISTG(X86_TRAP_MC,	asm_exc_machine_check,	IST_INDEX_MCE),
+#endif
+};
+
 /**
  * idt_setup_early_pf - Initialize the idt table with early pagefault handler
  *
@@ -325,6 +335,9 @@ void __init idt_setup_apic_and_irq_gates(void)
 	idt_map_in_cea();
 	load_idt(&idt_descr);
 
+	/* Make the IDT table read only */
+	set_memory_ro((unsigned long)&idt_table, 1);
+
 	idt_setup_done = true;
 }
 

arch/x86/mm/fault.c

@@ -414,21 +414,13 @@ static int is_errata100(struct pt_regs *regs, unsigned long address)
 	return 0;
 }
 
+/* Pentium F0 0F C7 C8 bug workaround: */
 static int is_f00f_bug(struct pt_regs *regs, unsigned long address)
 {
 #ifdef CONFIG_X86_F00F_BUG
-	unsigned long nr;
-
-	/*
-	 * Pentium F0 0F C7 C8 bug workaround:
-	 */
-	if (boot_cpu_has_bug(X86_BUG_F00F)) {
-		nr = (address - idt_descr.address) >> 3;
-
-		if (nr == 6) {
-			handle_invalid_op(regs);
-			return 1;
-		}
+	if (boot_cpu_has_bug(X86_BUG_F00F) && idt_is_f00f_address(address)) {
+		handle_invalid_op(regs);
+		return 1;
 	}
 #endif
 	return 0;