x86/exceptions: Disconnect IST index and stack order

The entry order of the TSS.IST array and the order of the stack
storage/mapping are not required to be the same.

With the upcoming split of the debug stack this is going to fall apart as
the number of TSS.IST array entries stays the same while the actual stacks
are increasing.

Make them separate so that code like dumpstack can just utilize the mapping
order. The IST index is solely required for the actual TSS.IST array
initialization.

Signed-off-by: Thomas Gleixner <[e-mail]>
Signed-off-by: Borislav Petkov <[e-mail]>
Cc: Andy Lutomirski <[e-mail]>
Cc: Baoquan He <[e-mail]>
Cc: "Chang S. Bae" <[e-mail]>
Cc: Dominik Brodowski <[e-mail]>
Cc: Dou Liyang <[e-mail]>
Cc: "H. Peter Anvin" <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Jann Horn <[e-mail]>
Cc: Josh Poimboeuf <[e-mail]>
Cc: Kees Cook <[e-mail]>
Cc: "Kirill A. Shutemov" <[e-mail]>
Cc: Konrad Rzeszutek Wilk <[e-mail]>
Cc: Nicolai Stange <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Qian Cai <[e-mail]>
Cc: Sean Christopherson <[e-mail]>
Cc: x86-ml <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]

arch/x86/entry/entry_64.S

···
 	hv_stimer0_callback_vector hv_stimer0_vector_handler
 #endif /* CONFIG_HYPERV */
 
-idtentry debug			do_debug		has_error_code=0	paranoid=1 shift_ist=ESTACK_DB
+idtentry debug			do_debug		has_error_code=0	paranoid=1 shift_ist=IST_INDEX_DB
 idtentry int3			do_int3			has_error_code=0
 idtentry stack_segment		do_stack_segment	has_error_code=1
 

arch/x86/include/asm/cpu_entry_area.h

···
 	ESTACKS_MEMBERS(0)
 };
 
+/*
+ * The exception stack ordering in [cea_]exception_stacks
+ */
+enum exception_stack_ordering {
+	ESTACK_DF,
+	ESTACK_NMI,
+	ESTACK_DB,
+	ESTACK_MCE,
+	N_EXCEPTION_STACKS
+};
+
 #define CEA_ESTACK_SIZE(st)					\
 	sizeof(((struct cea_exception_stacks *)0)->st## _stack)
 

arch/x86/include/asm/page_64_types.h

···
 /*
  * The index for the tss.ist[] array. The hardware limit is 7 entries.
  */
-#define	ESTACK_DF		0
-#define	ESTACK_NMI		1
-#define	ESTACK_DB		2
-#define	ESTACK_MCE		3
-#define	N_EXCEPTION_STACKS	4
+#define	IST_INDEX_DF		0
+#define	IST_INDEX_NMI		1
+#define	IST_INDEX_DB		2
+#define	IST_INDEX_MCE		3
 
 /*
  * Set __PAGE_OFFSET to the most negative possible address +

arch/x86/include/asm/stacktrace.h

···
 
 #include <linux/uaccess.h>
 #include <linux/ptrace.h>
+
+#include <asm/cpu_entry_area.h>
 #include <asm/switch_to.h>
 
 enum stack_type {

arch/x86/kernel/cpu/common.c

···
 	 * set up and load the per-CPU TSS
 	 */
 	if (!t->x86_tss.ist[0]) {
-		t->x86_tss.ist[ESTACK_DF] = __this_cpu_ist_top_va(DF);
-		t->x86_tss.ist[ESTACK_NMI] = __this_cpu_ist_top_va(NMI);
-		t->x86_tss.ist[ESTACK_DB] = __this_cpu_ist_top_va(DB);
-		t->x86_tss.ist[ESTACK_MCE] = __this_cpu_ist_top_va(MCE);
-		per_cpu(debug_stack_addr, cpu) = t->x86_tss.ist[ESTACK_DB];
+		t->x86_tss.ist[IST_INDEX_DF] = __this_cpu_ist_top_va(DF);
+		t->x86_tss.ist[IST_INDEX_NMI] = __this_cpu_ist_top_va(NMI);
+		t->x86_tss.ist[IST_INDEX_DB] = __this_cpu_ist_top_va(DB);
+		t->x86_tss.ist[IST_INDEX_MCE] = __this_cpu_ist_top_va(MCE);
+		per_cpu(debug_stack_addr, cpu) = t->x86_tss.ist[IST_INDEX_DB];
 	}
 
 	t->x86_tss.io_bitmap_base = IO_BITMAP_OFFSET;

arch/x86/kernel/idt.c

···
  * cpu_init() when the TSS has been initialized.
  */
 static const __initconst struct idt_data ist_idts[] = {
-	ISTG(X86_TRAP_DB,	debug,		ESTACK_DB),
-	ISTG(X86_TRAP_NMI,	nmi,		ESTACK_NMI),
-	ISTG(X86_TRAP_DF,	double_fault,	ESTACK_DF),
+	ISTG(X86_TRAP_DB,	debug,		IST_INDEX_DB),
+	ISTG(X86_TRAP_NMI,	nmi,		IST_INDEX_NMI),
+	ISTG(X86_TRAP_DF,	double_fault,	IST_INDEX_DF),
 #ifdef CONFIG_X86_MCE
-	ISTG(X86_TRAP_MC,	&machine_check,	ESTACK_MCE),
+	ISTG(X86_TRAP_MC,	&machine_check,	IST_INDEX_MCE),
 #endif
 };