x86/dumpstack/64: Use cpu_entry_area instead of orig_ist

The orig_ist[] array is a shadow copy of the IST array in the TSS. The
reason why it exists is that older kernels used two TSS variants with
different pointers into the debug stack. orig_ist[] contains the real
starting points.

There is no point anymore to do so because the same information can be
retrieved using the base address of the cpu entry area mapping and the
offsets of the various exception stacks.

No functional change. Preparation for removing orig_ist.

Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20190414160144.974900463@linutronix.de

arch/x86/kernel/dumpstack_64.c

@@ -16,6 +16,7 @@
 #include <linux/bug.h>
 #include <linux/nmi.h>
 
+#include <asm/cpu_entry_area.h>
 #include <asm/stacktrace.h>
 
 static const char *exception_stack_names[N_EXCEPTION_STACKS] = {
@@ -25,11 +26,6 @@ static const char *exception_stack_names[N_EXCEPTION_STACKS] = {
 		[ ESTACK_MCE	]	= "#MC",
 };
 
-static const unsigned long exception_stack_sizes[N_EXCEPTION_STACKS] = {
-	[0 ... N_EXCEPTION_STACKS - 1]		= EXCEPTION_STKSZ,
-	[ESTACK_DB]				= DEBUG_STKSZ
-};
-
 const char *stack_type_name(enum stack_type type)
 {
 	BUILD_BUG_ON(N_EXCEPTION_STACKS != 4);
@@ -52,25 +48,44 @@ const char *stack_type_name(enum stack_type type)
 	return NULL;
 }
 
+struct estack_layout {
+	unsigned int	begin;
+	unsigned int	end;
+};
+
+#define	ESTACK_ENTRY(x)	{						  \
+	.begin	= offsetof(struct cea_exception_stacks, x## _stack),	  \
+	.end	= offsetof(struct cea_exception_stacks, x## _stack_guard) \
+	}
+
+static const struct estack_layout layout[N_EXCEPTION_STACKS] = {
+	[ ESTACK_DF	]	= ESTACK_ENTRY(DF),
+	[ ESTACK_NMI	]	= ESTACK_ENTRY(NMI),
+	[ ESTACK_DB	]	= ESTACK_ENTRY(DB),
+	[ ESTACK_MCE	]	= ESTACK_ENTRY(MCE),
+};
+
 static bool in_exception_stack(unsigned long *stack, struct stack_info *info)
 {
-	unsigned long *begin, *end;
+	unsigned long estacks, begin, end, stk = (unsigned long)stack;
 	struct pt_regs *regs;
-	unsigned k;
+	unsigned int k;
 
 	BUILD_BUG_ON(N_EXCEPTION_STACKS != 4);
 
+	estacks = (unsigned long)__this_cpu_read(cea_exception_stacks);
+
 	for (k = 0; k < N_EXCEPTION_STACKS; k++) {
-		end   = (unsigned long *)raw_cpu_ptr(&orig_ist)->ist[k];
-		begin = end - (exception_stack_sizes[k] / sizeof(long));
+		begin = estacks + layout[k].begin;
+		end   = estacks + layout[k].end;
 		regs  = (struct pt_regs *)end - 1;
 
-		if (stack < begin || stack >= end)
+		if (stk < begin || stk >= end)
 			continue;
 
 		info->type	= STACK_TYPE_EXCEPTION + k;
-		info->begin	= begin;
-		info->end	= end;
+		info->begin	= (unsigned long *)begin;
+		info->end	= (unsigned long *)end;
 		info->next_sp	= (unsigned long *)regs->sp;
 
 		return true;