linux_kernel/arch/x86/include/asm/pgtable-3level.h

/* SPDX-License-Identifier: GPL-2.0 */
#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 <mingo@redhat.com>
 */

#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 native_pud_clear(pud_t *pudp)
{
}

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

#ifdef CONFIG_SMP
union split_pud {
	struct {
		u32 pud_low;
		u32 pud_high;
	};
	pud_t pud;
};

static inline pud_t native_pudp_get_and_clear(pud_t *pudp)
{
	union split_pud res, *orig = (union split_pud *)pudp;

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

	return res.pud;
}
#else
#define native_pudp_get_and_clear(xp) native_local_pudp_get_and_clear(xp)
#endif

/* 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 } })

#define gup_get_pte gup_get_pte
/*
 * WARNING: only to be used in the get_user_pages_fast() implementation.
 *
 * With get_user_pages_fast(), we walk down the pagetables without taking
 * any locks.  For this we would like to load the pointers atomically,
 * but that is not possible (without expensive cmpxchg8b) on PAE.  What
 * we do have is the guarantee that a PTE will only either go from not
 * present to present, or present to not present or both -- it will not
 * switch to a completely different present page without a TLB flush in
 * between; something that we are blocking by holding interrupts off.
 *
 * Setting ptes from not present to present goes:
 *
 *   ptep->pte_high = h;
 *   smp_wmb();
 *   ptep->pte_low = l;
 *
 * And present to not present goes:
 *
 *   ptep->pte_low = 0;
 *   smp_wmb();
 *   ptep->pte_high = 0;
 *
 * We must ensure here that the load of pte_low sees 'l' iff pte_high
 * sees 'h'. We load pte_high *after* loading pte_low, which ensures we
 * don't see an older value of pte_high.  *Then* we recheck pte_low,
 * which ensures that we haven't picked up a changed pte high. We might
 * have gotten rubbish values from pte_low and pte_high, but we are
 * guaranteed that pte_low will not have the present bit set *unless*
 * it is 'l'. Because get_user_pages_fast() only operates on present ptes
 * we're safe.
 */
static inline pte_t gup_get_pte(pte_t *ptep)
{
	pte_t pte;

	do {
		pte.pte_low = ptep->pte_low;
		smp_rmb();
		pte.pte_high = ptep->pte_high;
		smp_rmb();
	} while (unlikely(pte.pte_low != ptep->pte_low));

	return pte;
}

#endif /* _ASM_X86_PGTABLE_3LEVEL_H */