/*
 * This file contains common routines for dealing with free of page tables
 * Along with common page table handling code
 *
 *  Derived from arch/powerpc/mm/tlb_64.c:
 *    Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
 *
 *  Modifications by Paul Mackerras (PowerMac) (paulus@cs.anu.edu.au)
 *  and Cort Dougan (PReP) (cort@cs.nmt.edu)
 *    Copyright (C) 1996 Paul Mackerras
 *
 *  Derived from "arch/i386/mm/init.c"
 *    Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 *
 *  Dave Engebretsen <engebret@us.ibm.com>
 *      Rework for PPC64 port.
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License
 *  as published by the Free Software Foundation; either version
 *  2 of the License, or (at your option) any later version.
 */

#include <linux/kernel.h>
#include <linux/gfp.h>
#include <linux/mm.h>
#include <linux/percpu.h>
#include <linux/hardirq.h>
#include <linux/hugetlb.h>
#include <asm/pgalloc.h>
#include <asm/tlbflush.h>
#include <asm/tlb.h>

static inline int is_exec_fault(void)
{
        return current->thread.regs && TRAP(current->thread.regs) == 0x400;
}

/* We only try to do i/d cache coherency on stuff that looks like
 * reasonably "normal" PTEs. We currently require a PTE to be present
 * and we avoid _PAGE_SPECIAL and _PAGE_NO_CACHE. We also only do that
 * on userspace PTEs
 */
static inline int pte_looks_normal(pte_t pte)
{
        return (pte_val(pte) &
            (_PAGE_PRESENT | _PAGE_SPECIAL | _PAGE_NO_CACHE | _PAGE_USER)) ==
            (_PAGE_PRESENT | _PAGE_USER);
}

struct page * maybe_pte_to_page(pte_t pte)
{
        unsigned long pfn = pte_pfn(pte);
        struct page *page;

        if (unlikely(!pfn_valid(pfn)))
                return NULL;
        page = pfn_to_page(pfn);
        if (PageReserved(page))
                return NULL;
        return page;
}

#if defined(CONFIG_PPC_STD_MMU) || _PAGE_EXEC == 0

/* Server-style MMU handles coherency when hashing if HW exec permission
 * is supposed per page (currently 64-bit only). If not, then, we always
 * flush the cache for valid PTEs in set_pte. Embedded CPU without HW exec
 * support falls into the same category.
 */

static pte_t set_pte_filter(pte_t pte)
{
        pte = __pte(pte_val(pte) & ~_PAGE_HPTEFLAGS);
        if (pte_looks_normal(pte) && !(cpu_has_feature(CPU_FTR_COHERENT_ICACHE) ||
                                       cpu_has_feature(CPU_FTR_NOEXECUTE))) {
                struct page *pg = maybe_pte_to_page(pte);
                if (!pg)
                        return pte;
                if (!test_bit(PG_arch_1, &pg->flags)) {
                        flush_dcache_icache_page(pg);
                        set_bit(PG_arch_1, &pg->flags);
                }
        }
        return pte;
}

static pte_t set_access_flags_filter(pte_t pte, struct vm_area_struct *vma,
                                     int dirty)
{
        return pte;
}

#else /* defined(CONFIG_PPC_STD_MMU) || _PAGE_EXEC == 0 */

/* Embedded type MMU with HW exec support. This is a bit more complicated
 * as we don't have two bits to spare for _PAGE_EXEC and _PAGE_HWEXEC so
 * instead we "filter out" the exec permission for non clean pages.
 */
static pte_t set_pte_filter(pte_t pte)
{
        struct page *pg;

        /* No exec permission in the first place, move on */
        if (!(pte_val(pte) & _PAGE_EXEC) || !pte_looks_normal(pte))
                return pte;

        /* If you set _PAGE_EXEC on weird pages you're on your own */
        pg = maybe_pte_to_page(pte);
        if (unlikely(!pg))
                return pte;

        /* If the page clean, we move on */
        if (test_bit(PG_arch_1, &pg->flags))
                return pte;

        /* If it's an exec fault, we flush the cache and make it clean */
        if (is_exec_fault()) {
                flush_dcache_icache_page(pg);
                set_bit(PG_arch_1, &pg->flags);
                return pte;
        }

        /* Else, we filter out _PAGE_EXEC */
        return __pte(pte_val(pte) & ~_PAGE_EXEC);
}

static pte_t set_access_flags_filter(pte_t pte, struct vm_area_struct *vma,
                                     int dirty)
{
        struct page *pg;

        /* So here, we only care about exec faults, as we use them
         * to recover lost _PAGE_EXEC and perform I$/D$ coherency
         * if necessary. Also if _PAGE_EXEC is already set, same deal,
         * we just bail out
         */
        if (dirty || (pte_val(pte) & _PAGE_EXEC) || !is_exec_fault())
                return pte;

#ifdef CONFIG_DEBUG_VM
        /* So this is an exec fault, _PAGE_EXEC is not set. If it was
         * an error we would have bailed out earlier in do_page_fault()
         * but let's make sure of it
         */
        if (WARN_ON(!(vma->vm_flags & VM_EXEC)))
                return pte;
#endif /* CONFIG_DEBUG_VM */

        /* If you set _PAGE_EXEC on weird pages you're on your own */
        pg = maybe_pte_to_page(pte);
        if (unlikely(!pg))
                goto bail;

        /* If the page is already clean, we move on */
        if (test_bit(PG_arch_1, &pg->flags))
                goto bail;

        /* Clean the page and set PG_arch_1 */
        flush_dcache_icache_page(pg);
        set_bit(PG_arch_1, &pg->flags);

 bail:
        return __pte(pte_val(pte) | _PAGE_EXEC);
}

#endif /* !(defined(CONFIG_PPC_STD_MMU) || _PAGE_EXEC == 0) */

/*
 * set_pte stores a linux PTE into the linux page table.
 */
void set_pte_at(struct mm_struct *mm, unsigned long addr, pte_t *ptep,
                pte_t pte)
{
#ifdef CONFIG_DEBUG_VM
        WARN_ON(pte_val(*ptep) & _PAGE_PRESENT);
#endif
        /* Note: mm->context.id might not yet have been assigned as
         * this context might not have been activated yet when this
         * is called.
         */
        pte = set_pte_filter(pte);

        /* Perform the setting of the PTE */
        __set_pte_at(mm, addr, ptep, pte, 0);
}

/*
 * This is called when relaxing access to a PTE. It's also called in the page
 * fault path when we don't hit any of the major fault cases, ie, a minor
 * update of _PAGE_ACCESSED, _PAGE_DIRTY, etc... The generic code will have
 * handled those two for us, we additionally deal with missing execute
 * permission here on some processors
 */
int ptep_set_access_flags(struct vm_area_struct *vma, unsigned long address,
                          pte_t *ptep, pte_t entry, int dirty)
{
        int changed;
        entry = set_access_flags_filter(entry, vma, dirty);
        changed = !pte_same(*(ptep), entry);
        if (changed) {
                if (!is_vm_hugetlb_page(vma))
                        assert_pte_locked(vma->vm_mm, address);
                __ptep_set_access_flags(ptep, entry);
                flush_tlb_page_nohash(vma, address);
        }
        return changed;
}

#ifdef CONFIG_DEBUG_VM
void assert_pte_locked(struct mm_struct *mm, unsigned long addr)
{
        pgd_t *pgd;
        pud_t *pud;
        pmd_t *pmd;

        if (mm == &init_mm)
                return;
        pgd = mm->pgd + pgd_index(addr);
        BUG_ON(pgd_none(*pgd));
        pud = pud_offset(pgd, addr);
        BUG_ON(pud_none(*pud));
        pmd = pmd_offset(pud, addr);
        /*
         * khugepaged to collapse normal pages to hugepage, first set
         * pmd to none to force page fault/gup to take mmap_sem. After
         * pmd is set to none, we do a pte_clear which does this assertion
         * so if we find pmd none, return.
         */
        if (pmd_none(*pmd))
                return;
        BUG_ON(!pmd_present(*pmd));
        assert_spin_locked(pte_lockptr(mm, pmd));
}
#endif /* CONFIG_DEBUG_VM */