Function pmap_fault

freebsd/arm/arm/pmap-v6.c:6404–6609

* Handle access and R/W emulation faults. */

 *  Handle access and R/W emulation faults.
 */
int
pmap_fault(pmap_t pmap, vm_offset_t far, uint32_t fsr, int idx, bool usermode)
{
	pt1_entry_t *pte1p, pte1;
	pt2_entry_t *pte2p, pte2;

	if (pmap == NULL)
		pmap = kernel_pmap;

	/*
	 * In kernel, we should never get abort with FAR which is in range of
	 * pmap->pm_pt1 or PT2MAP address spaces. If it happens, stop here
	 * and print out a useful abort message and even get to the debugger
	 * otherwise it likely ends with never ending loop of aborts.
	 */
	if (__predict_false(IN_RANGE2(far, pmap->pm_pt1, NB_IN_PT1))) {
		/*
		 * All L1 tables should always be mapped and present.
		 * However, we check only current one herein. For user mode,
		 * only permission abort from malicious user is not fatal.
		 * And alignment abort as it may have higher priority.
		 */
		if (!usermode || (idx != FAULT_ALIGN && idx != FAULT_PERM_L2)) {
			CTR4(KTR_PMAP, "%s: pmap %#x pm_pt1 %#x far %#x",
			    __func__, pmap, pmap->pm_pt1, far);
			panic("%s: pm_pt1 abort", __func__);
		}
		return (KERN_INVALID_ADDRESS);
	}
	if (__predict_false(IN_RANGE2(far, PT2MAP, PT2MAP_SIZE))) {
		/*
		 * PT2MAP should be always mapped and present in current
		 * L1 table. However, only existing L2 tables are mapped
		 * in PT2MAP. For user mode, only L2 translation abort and
		 * permission abort from malicious user is not fatal.
		 * And alignment abort as it may have higher priority.
		 */
		if (!usermode || (idx != FAULT_ALIGN &&
		    idx != FAULT_TRAN_L2 && idx != FAULT_PERM_L2)) {
			CTR4(KTR_PMAP, "%s: pmap %#x PT2MAP %#x far %#x",
			    __func__, pmap, PT2MAP, far);
			panic("%s: PT2MAP abort", __func__);
		}
		return (KERN_INVALID_ADDRESS);
	}

	/*
	 * A pmap lock is used below for handling of access and R/W emulation
	 * aborts. They were handled by atomic operations before so some
	 * analysis of new situation is needed to answer the following question:
	 * Is it safe to use the lock even for these aborts?
	 *
	 * There may happen two cases in general:
	 *
	 * (1) Aborts while the pmap lock is locked already - this should not
	 * happen as pmap lock is not recursive. However, under pmap lock only
	 * internal kernel data should be accessed and such data should be
	 * mapped with A bit set and NM bit cleared. If double abort happens,