x86/mm: Fix exception table comments

		flags |= FAULT_FLAG_INSTRUCTION;

	/*

	 * When running in the kernel we expect faults to occur only to

	 * addresses in user space.  All other faults represent errors in

	 * the kernel and should generate an OOPS.  Unfortunately, in the

	 * case of an erroneous fault occurring in a code path which already

	 * holds mmap_sem we will deadlock attempting to validate the fault

	 * against the address space.  Luckily the kernel only validly

	 * references user space from well defined areas of code, which are

	 * listed in the exceptions table.

	 * Kernel-mode access to the user address space should only occur

	 * on well-defined single instructions listed in the exception

	 * tables.  But, an erroneous kernel fault occurring outside one of

	 * those areas which also holds mmap_sem might deadlock attempting

	 * to validate the fault against the address space.

	 *

	 * As the vast majority of faults will be valid we will only perform

	 * the source reference check when there is a possibility of a

	 * deadlock. Attempt to lock the address space, if we cannot we then

	 * validate the source. If this is invalid we can skip the address

	 * space check, thus avoiding the deadlock:

	 * Only do the expensive exception table search when we might be at

	 * risk of a deadlock.  This happens if we

	 * 1. Failed to acquire mmap_sem, and

	 * 2. The access did not originate in userspace.  Note: either the

	 *    hardware or earlier page fault code may set X86_PF_USER

	 *    in sw_error_code.

	 */

	if (unlikely(!down_read_trylock(&mm->mmap_sem))) {

		if (!(sw_error_code & X86_PF_USER) &&

		    !search_exception_tables(regs->ip)) {

			/*

			 * Fault from code in kernel from

			 * which we do not expect faults.

			 */

			bad_area_nosemaphore(regs, sw_error_code, address, NULL);

			return;

		}