x86/entry, nmi: Disable #DB

};

static DEFINE_PER_CPU(enum nmi_states, nmi_state);

static DEFINE_PER_CPU(unsigned long, nmi_cr2);

#ifdef CONFIG_X86_64

/*

 * In x86_64, we need to handle breakpoint -> NMI -> breakpoint.  Without

 * some care, the inner breakpoint will clobber the outer breakpoint's

 * stack.

 *

 * If a breakpoint is being processed, and the debug stack is being

 * used, if an NMI comes in and also hits a breakpoint, the stack

 * pointer will be set to the same fixed address as the breakpoint that

 * was interrupted, causing that stack to be corrupted. To handle this

 * case, check if the stack that was interrupted is the debug stack, and

 * if so, change the IDT so that new breakpoints will use the current

 * stack and not switch to the fixed address. On return of the NMI,

 * switch back to the original IDT.

 */

static DEFINE_PER_CPU(int, update_debug_stack);

static noinstr bool is_debug_stack(unsigned long addr)

{

	struct cea_exception_stacks *cs = __this_cpu_read(cea_exception_stacks);

	unsigned long top = CEA_ESTACK_TOP(cs, DB);

	unsigned long bot = CEA_ESTACK_BOT(cs, DB1);

	if (__this_cpu_read(debug_stack_usage))

		return true;

	/*

	 * Note, this covers the guard page between DB and DB1 as well to

	 * avoid two checks. But by all means @addr can never point into

	 * the guard page.

	 */

	return addr >= bot && addr < top;

}

#endif

static DEFINE_PER_CPU(unsigned long, nmi_dr7);

DEFINE_IDTENTRY_NMI(exc_nmi)

{

	this_cpu_write(nmi_cr2, read_cr2());

nmi_restart:

#ifdef CONFIG_X86_64

	/*

	 * If we interrupted a breakpoint, it is possible that

	 * the nmi handler will have breakpoints too. We need to

	 * change the IDT such that breakpoints that happen here

	 * continue to use the NMI stack.

	 */

	if (unlikely(is_debug_stack(regs->sp))) {

		debug_stack_set_zero();

		this_cpu_write(update_debug_stack, 1);

	}

#endif

	this_cpu_write(nmi_dr7, local_db_save());

	nmi_enter();

	nmi_exit();

#ifdef CONFIG_X86_64

	if (unlikely(this_cpu_read(update_debug_stack))) {

		debug_stack_reset();

		this_cpu_write(update_debug_stack, 0);

	}

#endif

	local_db_restore(this_cpu_read(nmi_dr7));

	if (unlikely(this_cpu_read(nmi_cr2) != read_cr2()))

		write_cr2(this_cpu_read(nmi_cr2));