// SPDX-License-Identifier: GPL-2.0
// Copyright (C) 2005-2017 Andes Technology Corporation

#include <linux/extable.h>
#include <linux/module.h>
#include <linux/signal.h>
#include <linux/ptrace.h>
#include <linux/mm.h>
#include <linux/init.h>
#include <linux/hardirq.h>
#include <linux/uaccess.h>
#include <linux/perf_event.h>

#include <asm/pgtable.h>
#include <asm/tlbflush.h>

extern void die(const char *str, struct pt_regs *regs, long err);

/*
 * This is useful to dump out the page tables associated with
 * 'addr' in mm 'mm'.
 */
void show_pte(struct mm_struct *mm, unsigned long addr)
{
	pgd_t *pgd;
	if (!mm)
		mm = &init_mm;

	pr_alert("pgd = %p\n", mm->pgd);
	pgd = pgd_offset(mm, addr);
	pr_alert("[%08lx] *pgd=%08lx", addr, pgd_val(*pgd));

	do {
		p4d_t *p4d;
		pud_t *pud;
		pmd_t *pmd;

		if (pgd_none(*pgd))
			break;

		if (pgd_bad(*pgd)) {
			pr_alert("(bad)");
			break;
		}

		p4d = p4d_offset(pgd, addr);
		pud = pud_offset(p4d, addr);
		pmd = pmd_offset(pud, addr);
#if PTRS_PER_PMD != 1
		pr_alert(", *pmd=%08lx", pmd_val(*pmd));
#endif

		if (pmd_none(*pmd))
			break;

		if (pmd_bad(*pmd)) {
			pr_alert("(bad)");
			break;
		}

		if (IS_ENABLED(CONFIG_HIGHMEM))
		{
			pte_t *pte;
			/* We must not map this if we have highmem enabled */
			pte = pte_offset_map(pmd, addr);
			pr_alert(", *pte=%08lx", pte_val(*pte));
			pte_unmap(pte);
		}
	} while (0);

	pr_alert("\n");
}

void do_page_fault(unsigned long entry, unsigned long addr,
		   unsigned int error_code, struct pt_regs *regs)
{
	struct task_struct *tsk;
	struct mm_struct *mm;
	struct vm_area_struct *vma;
	int si_code;
	vm_fault_t fault;
	unsigned int mask = VM_READ | VM_WRITE | VM_EXEC;
	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;

	error_code = error_code & (ITYPE_mskINST | ITYPE_mskETYPE);
	tsk = current;
	mm = tsk->mm;
	si_code = SEGV_MAPERR;
	/*
	 * We fault-in kernel-space virtual memory on-demand. The
	 * 'reference' page table is init_mm.pgd.
	 *
	 * NOTE! We MUST NOT take any locks for this case. We may
	 * be in an interrupt or a critical region, and should
	 * only copy the information from the master page table,
	 * nothing more.
	 */
	if (addr >= TASK_SIZE) {
		if (user_mode(regs))
			goto bad_area_nosemaphore;

		if (addr >= TASK_SIZE && addr < VMALLOC_END
		    && (entry == ENTRY_PTE_NOT_PRESENT))
			goto vmalloc_fault;
		else
			goto no_context;
	}

	/* Send a signal to the task for handling the unalignment access. */
	if (entry == ENTRY_GENERAL_EXCPETION
	    && error_code == ETYPE_ALIGNMENT_CHECK) {
		if (user_mode(regs))
			goto bad_area_nosemaphore;
		else
			goto no_context;
	}

	/*
	 * If we're in an interrupt or have no user
	 * context, we must not take the fault..
	 */
	if (unlikely(faulthandler_disabled() || !mm))
		goto no_context;

	/*
	 * As per x86, we may deadlock here. However, since the kernel only
	 * validly references user space from well defined areas of the code,
	 * we can bug out early if this is from code which shouldn't.
	 */
	if (unlikely(!down_read_trylock(&mm->mmap_sem))) {
		if (!user_mode(regs) &&
		    !search_exception_tables(instruction_pointer(regs)))
			goto no_context;
retry:
		down_read(&mm->mmap_sem);
	} else {
		/*
		 * The above down_read_trylock() might have succeeded in which
		 * case, we'll have missed the might_sleep() from down_read().
		 */
		might_sleep();
		if (IS_ENABLED(CONFIG_DEBUG_VM)) {
			if (!user_mode(regs) &&
			    !search_exception_tables(instruction_pointer(regs)))
				goto no_context;
		}
	}

	vma = find_vma(mm, addr);

	if (unlikely(!vma))
		goto bad_area;

	if (vma->vm_start <= addr)
		goto good_area;

	if (unlikely(!(vma->vm_flags & VM_GROWSDOWN)))
		goto bad_area;

	if (unlikely(expand_stack(vma, addr)))
		goto bad_area;

	/*
	 * Ok, we have a good vm_area for this memory access, so
	 * we can handle it..
	 */

good_area:
	si_code = SEGV_ACCERR;

	/* first do some preliminary protection checks */
	if (entry == ENTRY_PTE_NOT_PRESENT) {
		if (error_code & ITYPE_mskINST)
			mask = VM_EXEC;
		else {
			mask = VM_READ | VM_WRITE;
		}
	} else if (entry == ENTRY_TLB_MISC) {
		switch (error_code & ITYPE_mskETYPE) {
		case RD_PROT:
			mask = VM_READ;
			break;
		case WRT_PROT:
			mask = VM_WRITE;
			flags |= FAULT_FLAG_WRITE;
			break;
		case NOEXEC:
			mask = VM_EXEC;
			break;
		case PAGE_MODIFY:
			mask = VM_WRITE;
			flags |= FAULT_FLAG_WRITE;
			break;
		case ACC_BIT:
			BUG();
		default:
			break;
		}

	}
	if (!(vma->vm_flags & mask))
		goto bad_area;

	/*
	 * If for any reason at all we couldn't handle the fault,
	 * make sure we exit gracefully rather than endlessly redo
	 * the fault.
	 */

	fault = handle_mm_fault(vma, addr, flags);

	/*
	 * If we need to retry but a fatal signal is pending, handle the
	 * signal first. We do not need to release the mmap_sem because it
	 * would already be released in __lock_page_or_retry in mm/filemap.c.
	 */
	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) {
		if (!user_mode(regs))
			goto no_context;
		return;
	}

	if (unlikely(fault & VM_FAULT_ERROR)) {
		if (fault & VM_FAULT_OOM)
			goto out_of_memory;
		else if (fault & VM_FAULT_SIGBUS)
			goto do_sigbus;
		else
			goto bad_area;
	}

	/*
	 * Major/minor page fault accounting is only done on the initial
	 * attempt. If we go through a retry, it is extremely likely that the
	 * page will be found in page cache at that point.
	 */
	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);
	if (flags & FAULT_FLAG_ALLOW_RETRY) {
		if (fault & VM_FAULT_MAJOR) {
			tsk->maj_flt++;
			perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ,
				      1, regs, addr);
		} else {
			tsk->min_flt++;
			perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN,
				      1, regs, addr);
		}
		if (fault & VM_FAULT_RETRY) {
			flags &= ~FAULT_FLAG_ALLOW_RETRY;
			flags |= FAULT_FLAG_TRIED;

			/* No need to up_read(&mm->mmap_sem) as we would
			 * have already released it in __lock_page_or_retry
			 * in mm/filemap.c.
			 */
			goto retry;
		}
	}

	up_read(&mm->mmap_sem);
	return;

	/*
	 * Something tried to access memory that isn't in our memory map..
	 * Fix it, but check if it's kernel or user first..
	 */
bad_area:
	up_read(&mm->mmap_sem);

bad_area_nosemaphore:

	/* User mode accesses just cause a SIGSEGV */

	if (user_mode(regs)) {
		tsk->thread.address = addr;
		tsk->thread.error_code = error_code;
		tsk->thread.trap_no = entry;
		force_sig_fault(SIGSEGV, si_code, (void __user *)addr);
		return;
	}

no_context:

	/* Are we prepared to handle this kernel fault?
	 *
	 * (The kernel has valid exception-points in the source
	 *  when it acesses user-memory. When it fails in one
	 *  of those points, we find it in a table and do a jump
	 *  to some fixup code that loads an appropriate error
	 *  code)
	 */

	{
		const struct exception_table_entry *entry;

		if ((entry =
		     search_exception_tables(instruction_pointer(regs))) !=
		    NULL) {
			/* Adjust the instruction pointer in the stackframe */
			instruction_pointer(regs) = entry->fixup;
			return;
		}
	}

	/*
	 * Oops. The kernel tried to access some bad page. We'll have to
	 * terminate things with extreme prejudice.
	 */

	bust_spinlocks(1);
	pr_alert("Unable to handle kernel %s at virtual address %08lx\n",
		 (addr < PAGE_SIZE) ? "NULL pointer dereference" :
		 "paging request", addr);

	show_pte(mm, addr);
	die("Oops", regs, error_code);
	bust_spinlocks(0);
	do_exit(SIGKILL);

	return;

	/*
	 * We ran out of memory, or some other thing happened to us that made
	 * us unable to handle the page fault gracefully.
	 */

out_of_memory:
	up_read(&mm->mmap_sem);
	if (!user_mode(regs))
		goto no_context;
	pagefault_out_of_memory();
	return;

do_sigbus:
	up_read(&mm->mmap_sem);

	/* Kernel mode? Handle exceptions or die */
	if (!user_mode(regs))
		goto no_context;

	/*
	 * Send a sigbus
	 */
	tsk->thread.address = addr;
	tsk->thread.error_code = error_code;
	tsk->thread.trap_no = entry;
	force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)addr);

	return;

vmalloc_fault:
	{
		/*
		 * Synchronize this task's top level page-table
		 * with the 'reference' page table.
		 *
		 * Use current_pgd instead of tsk->active_mm->pgd
		 * since the latter might be unavailable if this
		 * code is executed in a misfortunately run irq
		 * (like inside schedule() between switch_mm and
		 *  switch_to...).
		 */

		unsigned int index = pgd_index(addr);
		pgd_t *pgd, *pgd_k;
		p4d_t *p4d, *p4d_k;
		pud_t *pud, *pud_k;
		pmd_t *pmd, *pmd_k;
		pte_t *pte_k;

		pgd = (pgd_t *) __va(__nds32__mfsr(NDS32_SR_L1_PPTB)) + index;
		pgd_k = init_mm.pgd + index;

		if (!pgd_present(*pgd_k))
			goto no_context;

		p4d = p4d_offset(pgd, addr);
		p4d_k = p4d_offset(pgd_k, addr);
		if (!p4d_present(*p4d_k))
			goto no_context;

		pud = pud_offset(p4d, addr);
		pud_k = pud_offset(p4d_k, addr);
		if (!pud_present(*pud_k))
			goto no_context;

		pmd = pmd_offset(pud, addr);
		pmd_k = pmd_offset(pud_k, addr);
		if (!pmd_present(*pmd_k))
			goto no_context;

		if (!pmd_present(*pmd))
			set_pmd(pmd, *pmd_k);
		else
			BUG_ON(pmd_page(*pmd) != pmd_page(*pmd_k));

		/*
		 * Since the vmalloc area is global, we don't
		 * need to copy individual PTE's, it is enough to
		 * copy the pgd pointer into the pte page of the
		 * root task. If that is there, we'll find our pte if
		 * it exists.
		 */

		/* Make sure the actual PTE exists as well to
		 * catch kernel vmalloc-area accesses to non-mapped
		 * addres. If we don't do this, this will just
		 * silently loop forever.
		 */

		pte_k = pte_offset_kernel(pmd_k, addr);
		if (!pte_present(*pte_k))
			goto no_context;

		return;
	}
}