pgtable-3level.h

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#ifndef _ASM_X86_PGTABLE_3LEVEL_H
#define _ASM_X86_PGTABLE_3LEVEL_H

/*
 * Intel Physical Address Extension (PAE) Mode - three-level page
 * tables on PPro+ CPUs.
 *
 * Copyright (C) 1999 Ingo Molnar <[email protected]>
 */

#define pte_ERROR(e)                            \
    pr_err("%s:%d: bad pte %p(%08lx%08lx)\n",           \
           __FILE__, __LINE__, &(e), (e).pte_high, (e).pte_low)
#define pmd_ERROR(e)                            \
    pr_err("%s:%d: bad pmd %p(%016Lx)\n",               \
           __FILE__, __LINE__, &(e), pmd_val(e))
#define pgd_ERROR(e)                            \
    pr_err("%s:%d: bad pgd %p(%016Lx)\n",               \
           __FILE__, __LINE__, &(e), pgd_val(e))

/* Rules for using set_pte: the pte being assigned *must* be
 * either not present or in a state where the hardware will
 * not attempt to update the pte.  In places where this is
 * not possible, use pte_get_and_clear to obtain the old pte
 * value and then use set_pte to update it.  -ben
 */
static inline void native_set_pte(pte_t *ptep, pte_t pte)
{
    ptep->pte_high = pte.pte_high;
    smp_wmb();
    ptep->pte_low = pte.pte_low;
}

#define pmd_read_atomic pmd_read_atomic
/*
 * pte_offset_map_lock on 32bit PAE kernels was reading the pmd_t with
 * a "*pmdp" dereference done by gcc. Problem is, in certain places
 * where pte_offset_map_lock is called, concurrent page faults are
 * allowed, if the mmap_sem is hold for reading. An example is mincore
 * vs page faults vs MADV_DONTNEED. On the page fault side
 * pmd_populate rightfully does a set_64bit, but if we're reading the
 * pmd_t with a "*pmdp" on the mincore side, a SMP race can happen
 * because gcc will not read the 64bit of the pmd atomically. To fix
 * this all places running pmd_offset_map_lock() while holding the
 * mmap_sem in read mode, shall read the pmdp pointer using this
 * function to know if the pmd is null nor not, and in turn to know if
 * they can run pmd_offset_map_lock or pmd_trans_huge or other pmd
 * operations.
 *
 * Without THP if the mmap_sem is hold for reading, the pmd can only
 * transition from null to not null while pmd_read_atomic runs. So
 * we can always return atomic pmd values with this function.
 *
 * With THP if the mmap_sem is hold for reading, the pmd can become
 * trans_huge or none or point to a pte (and in turn become "stable")
 * at any time under pmd_read_atomic. We could read it really
 * atomically here with a atomic64_read for the THP enabled case (and
 * it would be a whole lot simpler), but to avoid using cmpxchg8b we
 * only return an atomic pmdval if the low part of the pmdval is later
 * found stable (i.e. pointing to a pte). And we're returning a none
 * pmdval if the low part of the pmd is none. In some cases the high
 * and low part of the pmdval returned may not be consistent if THP is
 * enabled (the low part may point to previously mapped hugepage,
 * while the high part may point to a more recently mapped hugepage),
 * but pmd_none_or_trans_huge_or_clear_bad() only needs the low part
 * of the pmd to be read atomically to decide if the pmd is unstable
 * or not, with the only exception of when the low part of the pmd is
 * zero in which case we return a none pmd.
 */
static inline pmd_t pmd_read_atomic(pmd_t *pmdp)
{
    pmdval_t ret;
    u32 *tmp = (u32 *)pmdp;

    ret = (pmdval_t) (*tmp);
    if (ret) {
        /*
         * If the low part is null, we must not read the high part
         * or we can end up with a partial pmd.
         */
        smp_rmb();
        ret |= ((pmdval_t)*(tmp + 1)) << 32;
    }

    return (pmd_t) { ret };
}

static inline void native_set_pte_atomic(pte_t *ptep, pte_t pte)
{
    set_64bit((unsigned long long *)(ptep), native_pte_val(pte));
}

static inline void native_set_pmd(pmd_t *pmdp, pmd_t pmd)
{
    set_64bit((unsigned long long *)(pmdp), native_pmd_val(pmd));
}

static inline void native_set_pud(pud_t *pudp, pud_t pud)
{
    set_64bit((unsigned long long *)(pudp), native_pud_val(pud));
}

/*
 * For PTEs and PDEs, we must clear the P-bit first when clearing a page table
 * entry, so clear the bottom half first and enforce ordering with a compiler
 * barrier.
 */
static inline void native_pte_clear(struct mm_struct *mm, unsigned long addr,
                    pte_t *ptep)
{
    ptep->pte_low = 0;
    smp_wmb();
    ptep->pte_high = 0;
}

static inline void native_pmd_clear(pmd_t *pmd)
{
    u32 *tmp = (u32 *)pmd;
    *tmp = 0;
    smp_wmb();
    *(tmp + 1) = 0;
}

static inline void pud_clear(pud_t *pudp)
{
    set_pud(pudp, __pud(0));

    /*
     * According to Intel App note "TLBs, Paging-Structure Caches,
     * and Their Invalidation", April 2007, document 317080-001,
     * section 8.1: in PAE mode we explicitly have to flush the
     * TLB via cr3 if the top-level pgd is changed...
     *
     * Currently all places where pud_clear() is called either have
     * flush_tlb_mm() followed or don't need TLB flush (x86_64 code or
     * pud_clear_bad()), so we don't need TLB flush here.
     */
}

#ifdef CONFIG_SMP
static inline pte_t native_ptep_get_and_clear(pte_t *ptep)
{
    pte_t res;

    /* xchg acts as a barrier before the setting of the high bits */
    res.pte_low = xchg(&ptep->pte_low, 0);
    res.pte_high = ptep->pte_high;
    ptep->pte_high = 0;

    return res;
}
#else
#define native_ptep_get_and_clear(xp) native_local_ptep_get_and_clear(xp)
#endif

#ifdef CONFIG_SMP
union split_pmd {
    struct {
        u32 pmd_low;
        u32 pmd_high;
    };
    pmd_t pmd;
};
static inline pmd_t native_pmdp_get_and_clear(pmd_t *pmdp)
{
    union split_pmd res, *orig = (union split_pmd *)pmdp;

    /* xchg acts as a barrier before setting of the high bits */
    res.pmd_low = xchg(&orig->pmd_low, 0);
    res.pmd_high = orig->pmd_high;
    orig->pmd_high = 0;

    return res.pmd;
}
#else
#define native_pmdp_get_and_clear(xp) native_local_pmdp_get_and_clear(xp)
#endif

/*
 * Bits 0, 6 and 7 are taken in the low part of the pte,
 * put the 32 bits of offset into the high part.
 */
#define pte_to_pgoff(pte) ((pte).pte_high)
#define pgoff_to_pte(off)                       \
    ((pte_t) { { .pte_low = _PAGE_FILE, .pte_high = (off) } })
#define PTE_FILE_MAX_BITS       32

/* Encode and de-code a swap entry */
#define MAX_SWAPFILES_CHECK() BUILD_BUG_ON(MAX_SWAPFILES_SHIFT > 5)
#define __swp_type(x)           (((x).val) & 0x1f)
#define __swp_offset(x)         ((x).val >> 5)
#define __swp_entry(type, offset)   ((swp_entry_t){(type) | (offset) << 5})
#define __pte_to_swp_entry(pte)     ((swp_entry_t){ (pte).pte_high })
#define __swp_entry_to_pte(x)       ((pte_t){ { .pte_high = (x).val } })

#endif /* _ASM_X86_PGTABLE_3LEVEL_H */