// TODO VM_EXEC flag work-around, cache aliasing
/*
 * arch/xtensa/mm/fault.c
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 *
 * Copyright (C) 2001 - 2010 Tensilica Inc.
 *
 * Chris Zankel <chris@zankel.net>
 * Joe Taylor   <joe@tensilica.com, joetylr@yahoo.com>
 */

#include <linux/mm.h>
#include <linux/extable.h>
#include <linux/hardirq.h>
#include <linux/perf_event.h>
#include <linux/uaccess.h>
#include <asm/mmu_context.h>
#include <asm/cacheflush.h>
#include <asm/hardirq.h>
#include <asm/traps.h>

void bad_page_fault(struct pt_regs*, unsigned long, int);

static void vmalloc_fault(struct pt_regs *regs, unsigned int address)
{
#ifdef CONFIG_MMU
        /* Synchronize this task's top level page-table
         * with the 'reference' page table.
         */
        struct mm_struct *act_mm = current->active_mm;
        int index = pgd_index(address);
        pgd_t *pgd, *pgd_k;
        p4d_t *p4d, *p4d_k;
        pud_t *pud, *pud_k;
        pmd_t *pmd, *pmd_k;
        pte_t *pte_k;

        if (act_mm == NULL)
                goto bad_page_fault;

        pgd = act_mm->pgd + index;
        pgd_k = init_mm.pgd + index;

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

        pgd_val(*pgd) = pgd_val(*pgd_k);

        p4d = p4d_offset(pgd, address);
        p4d_k = p4d_offset(pgd_k, address);
        if (!p4d_present(*p4d) || !p4d_present(*p4d_k))
                goto bad_page_fault;

        pud = pud_offset(p4d, address);
        pud_k = pud_offset(p4d_k, address);
        if (!pud_present(*pud) || !pud_present(*pud_k))
                goto bad_page_fault;

        pmd = pmd_offset(pud, address);
        pmd_k = pmd_offset(pud_k, address);
        if (!pmd_present(*pmd) || !pmd_present(*pmd_k))
                goto bad_page_fault;

        pmd_val(*pmd) = pmd_val(*pmd_k);
        pte_k = pte_offset_kernel(pmd_k, address);

        if (!pte_present(*pte_k))
                goto bad_page_fault;
        return;

bad_page_fault:
        bad_page_fault(regs, address, SIGKILL);
#else
        WARN_ONCE(1, "%s in noMMU configuration\n", __func__);
#endif
}
/*
 * This routine handles page faults.  It determines the address,
 * and the problem, and then passes it off to one of the appropriate
 * routines.
 *
 * Note: does not handle Miss and MultiHit.
 */

void do_page_fault(struct pt_regs *regs)
{
        struct vm_area_struct * vma;
        struct mm_struct *mm = current->mm;
        unsigned int exccause = regs->exccause;
        unsigned int address = regs->excvaddr;
        int code;

        int is_write, is_exec;
        vm_fault_t fault;
        unsigned int flags = FAULT_FLAG_DEFAULT;

        code = SEGV_MAPERR;

        /* We fault-in kernel-space virtual memory on-demand. The
         * 'reference' page table is init_mm.pgd.
         */
        if (address >= TASK_SIZE && !user_mode(regs)) {
                vmalloc_fault(regs, address);
                return;
        }

        /* If we're in an interrupt or have no user
         * context, we must not take the fault..
         */
        if (faulthandler_disabled() || !mm) {
                bad_page_fault(regs, address, SIGSEGV);
                return;
        }

        is_write = (exccause == EXCCAUSE_STORE_CACHE_ATTRIBUTE) ? 1 : 0;
        is_exec =  (exccause == EXCCAUSE_ITLB_PRIVILEGE ||
                    exccause == EXCCAUSE_ITLB_MISS ||
                    exccause == EXCCAUSE_FETCH_CACHE_ATTRIBUTE) ? 1 : 0;

        pr_debug("[%s:%d:%08x:%d:%08lx:%s%s]\n",
                 current->comm, current->pid,
                 address, exccause, regs->pc,
                 is_write ? "w" : "", is_exec ? "x" : "");

        if (user_mode(regs))
                flags |= FAULT_FLAG_USER;

        perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);

retry:
        vma = lock_mm_and_find_vma(mm, address, regs);
        if (!vma)
                goto bad_area_nosemaphore;

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

        code = SEGV_ACCERR;

        if (is_write) {
                if (!(vma->vm_flags & VM_WRITE))
                        goto bad_area;
                flags |= FAULT_FLAG_WRITE;
        } else if (is_exec) {
                if (!(vma->vm_flags & VM_EXEC))
                        goto bad_area;
        } else  /* Allow read even from write-only pages. */
                if (!(vma->vm_flags & (VM_READ | VM_WRITE)))
                        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, address, flags, regs);

        if (fault_signal_pending(fault, regs)) {
                if (!user_mode(regs))
                        bad_page_fault(regs, address, SIGKILL);
                return;
        }

        /* The fault is fully completed (including releasing mmap lock) */
        if (fault & VM_FAULT_COMPLETED)
                return;

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

        if (fault & VM_FAULT_RETRY) {
                flags |= FAULT_FLAG_TRIED;

                /* No need to mmap_read_unlock(mm) as we would
                 * have already released it in __lock_page_or_retry
                 * in mm/filemap.c.
                 */

                goto retry;
        }

        mmap_read_unlock(mm);
        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:
        mmap_read_unlock(mm);
bad_area_nosemaphore:
        if (user_mode(regs)) {
                force_sig_fault(SIGSEGV, code, (void *) address);
                return;
        }
        bad_page_fault(regs, address, SIGSEGV);
        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:
        mmap_read_unlock(mm);
        if (!user_mode(regs))
                bad_page_fault(regs, address, SIGKILL);
        else
                pagefault_out_of_memory();
        return;

do_sigbus:
        mmap_read_unlock(mm);

        /* Send a sigbus, regardless of whether we were in kernel
         * or user mode.
         */
        force_sig_fault(SIGBUS, BUS_ADRERR, (void *) address);

        /* Kernel mode? Handle exceptions or die */
        if (!user_mode(regs))
                bad_page_fault(regs, address, SIGBUS);
        return;
}


void
bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
{
        extern void __noreturn die(const char*, struct pt_regs*, long);
        const struct exception_table_entry *entry;

        /* Are we prepared to handle this kernel fault?  */
        if ((entry = search_exception_tables(regs->pc)) != NULL) {
                pr_debug("%s: Exception at pc=%#010lx (%lx)\n",
                         current->comm, regs->pc, entry->fixup);
                regs->pc = entry->fixup;
                return;
        }

        /* Oops. The kernel tried to access some bad page. We'll have to
         * terminate things with extreme prejudice.
         */
        pr_alert("Unable to handle kernel paging request at virtual "
                 "address %08lx\n pc = %08lx, ra = %08lx\n",
                 address, regs->pc, regs->areg[0]);
        die("Oops", regs, sig);
}