linux/mm/page_vma_mapped.c
Peter Xu 9c67a20704 mm/hugetlb: introduce hugetlb_walk()
huge_pte_offset() is the main walker function for hugetlb pgtables.  The
name is not really representing what it does, though.

Instead of renaming it, introduce a wrapper function called hugetlb_walk()
which will use huge_pte_offset() inside.  Assert on the locks when walking
the pgtable.

Note, the vma lock assertion will be a no-op for private mappings.

Document the last special case in the page_vma_mapped_walk() path where we
don't need any more lock to call hugetlb_walk().

Taking vma lock there is not needed because either: (1) potential callers
of hugetlb pvmw holds i_mmap_rwsem already (from one rmap_walk()), or (2)
the caller will not walk a hugetlb vma at all so the hugetlb code path not
reachable (e.g.  in ksm or uprobe paths).

It's slightly implicit for future page_vma_mapped_walk() callers on that
lock requirement.  But anyway, when one day this rule breaks, one will get
a straightforward warning in hugetlb_walk() with lockdep, then there'll be
a way out.

[akpm@linux-foundation.org: coding-style cleanups]
Link: https://lkml.kernel.org/r/20221216155229.2043750-1-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: James Houghton <jthoughton@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Nadav Amit <nadav.amit@gmail.com>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-01-18 17:12:39 -08:00

320 lines
8.7 KiB
C

// SPDX-License-Identifier: GPL-2.0
#include <linux/mm.h>
#include <linux/rmap.h>
#include <linux/hugetlb.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include "internal.h"
static inline bool not_found(struct page_vma_mapped_walk *pvmw)
{
page_vma_mapped_walk_done(pvmw);
return false;
}
static bool map_pte(struct page_vma_mapped_walk *pvmw)
{
pvmw->pte = pte_offset_map(pvmw->pmd, pvmw->address);
if (!(pvmw->flags & PVMW_SYNC)) {
if (pvmw->flags & PVMW_MIGRATION) {
if (!is_swap_pte(*pvmw->pte))
return false;
} else {
/*
* We get here when we are trying to unmap a private
* device page from the process address space. Such
* page is not CPU accessible and thus is mapped as
* a special swap entry, nonetheless it still does
* count as a valid regular mapping for the page (and
* is accounted as such in page maps count).
*
* So handle this special case as if it was a normal
* page mapping ie lock CPU page table and returns
* true.
*
* For more details on device private memory see HMM
* (include/linux/hmm.h or mm/hmm.c).
*/
if (is_swap_pte(*pvmw->pte)) {
swp_entry_t entry;
/* Handle un-addressable ZONE_DEVICE memory */
entry = pte_to_swp_entry(*pvmw->pte);
if (!is_device_private_entry(entry) &&
!is_device_exclusive_entry(entry))
return false;
} else if (!pte_present(*pvmw->pte))
return false;
}
}
pvmw->ptl = pte_lockptr(pvmw->vma->vm_mm, pvmw->pmd);
spin_lock(pvmw->ptl);
return true;
}
/**
* check_pte - check if @pvmw->page is mapped at the @pvmw->pte
* @pvmw: page_vma_mapped_walk struct, includes a pair pte and page for checking
*
* page_vma_mapped_walk() found a place where @pvmw->page is *potentially*
* mapped. check_pte() has to validate this.
*
* pvmw->pte may point to empty PTE, swap PTE or PTE pointing to
* arbitrary page.
*
* If PVMW_MIGRATION flag is set, returns true if @pvmw->pte contains migration
* entry that points to @pvmw->page or any subpage in case of THP.
*
* If PVMW_MIGRATION flag is not set, returns true if pvmw->pte points to
* pvmw->page or any subpage in case of THP.
*
* Otherwise, return false.
*
*/
static bool check_pte(struct page_vma_mapped_walk *pvmw)
{
unsigned long pfn;
if (pvmw->flags & PVMW_MIGRATION) {
swp_entry_t entry;
if (!is_swap_pte(*pvmw->pte))
return false;
entry = pte_to_swp_entry(*pvmw->pte);
if (!is_migration_entry(entry) &&
!is_device_exclusive_entry(entry))
return false;
pfn = swp_offset_pfn(entry);
} else if (is_swap_pte(*pvmw->pte)) {
swp_entry_t entry;
/* Handle un-addressable ZONE_DEVICE memory */
entry = pte_to_swp_entry(*pvmw->pte);
if (!is_device_private_entry(entry) &&
!is_device_exclusive_entry(entry))
return false;
pfn = swp_offset_pfn(entry);
} else {
if (!pte_present(*pvmw->pte))
return false;
pfn = pte_pfn(*pvmw->pte);
}
return (pfn - pvmw->pfn) < pvmw->nr_pages;
}
/* Returns true if the two ranges overlap. Careful to not overflow. */
static bool check_pmd(unsigned long pfn, struct page_vma_mapped_walk *pvmw)
{
if ((pfn + HPAGE_PMD_NR - 1) < pvmw->pfn)
return false;
if (pfn > pvmw->pfn + pvmw->nr_pages - 1)
return false;
return true;
}
static void step_forward(struct page_vma_mapped_walk *pvmw, unsigned long size)
{
pvmw->address = (pvmw->address + size) & ~(size - 1);
if (!pvmw->address)
pvmw->address = ULONG_MAX;
}
/**
* page_vma_mapped_walk - check if @pvmw->pfn is mapped in @pvmw->vma at
* @pvmw->address
* @pvmw: pointer to struct page_vma_mapped_walk. page, vma, address and flags
* must be set. pmd, pte and ptl must be NULL.
*
* Returns true if the page is mapped in the vma. @pvmw->pmd and @pvmw->pte point
* to relevant page table entries. @pvmw->ptl is locked. @pvmw->address is
* adjusted if needed (for PTE-mapped THPs).
*
* If @pvmw->pmd is set but @pvmw->pte is not, you have found PMD-mapped page
* (usually THP). For PTE-mapped THP, you should run page_vma_mapped_walk() in
* a loop to find all PTEs that map the THP.
*
* For HugeTLB pages, @pvmw->pte is set to the relevant page table entry
* regardless of which page table level the page is mapped at. @pvmw->pmd is
* NULL.
*
* Returns false if there are no more page table entries for the page in
* the vma. @pvmw->ptl is unlocked and @pvmw->pte is unmapped.
*
* If you need to stop the walk before page_vma_mapped_walk() returned false,
* use page_vma_mapped_walk_done(). It will do the housekeeping.
*/
bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
{
struct vm_area_struct *vma = pvmw->vma;
struct mm_struct *mm = vma->vm_mm;
unsigned long end;
pgd_t *pgd;
p4d_t *p4d;
pud_t *pud;
pmd_t pmde;
/* The only possible pmd mapping has been handled on last iteration */
if (pvmw->pmd && !pvmw->pte)
return not_found(pvmw);
if (unlikely(is_vm_hugetlb_page(vma))) {
struct hstate *hstate = hstate_vma(vma);
unsigned long size = huge_page_size(hstate);
/* The only possible mapping was handled on last iteration */
if (pvmw->pte)
return not_found(pvmw);
/*
* All callers that get here will already hold the
* i_mmap_rwsem. Therefore, no additional locks need to be
* taken before calling hugetlb_walk().
*/
pvmw->pte = hugetlb_walk(vma, pvmw->address, size);
if (!pvmw->pte)
return false;
pvmw->ptl = huge_pte_lock(hstate, mm, pvmw->pte);
if (!check_pte(pvmw))
return not_found(pvmw);
return true;
}
end = vma_address_end(pvmw);
if (pvmw->pte)
goto next_pte;
restart:
do {
pgd = pgd_offset(mm, pvmw->address);
if (!pgd_present(*pgd)) {
step_forward(pvmw, PGDIR_SIZE);
continue;
}
p4d = p4d_offset(pgd, pvmw->address);
if (!p4d_present(*p4d)) {
step_forward(pvmw, P4D_SIZE);
continue;
}
pud = pud_offset(p4d, pvmw->address);
if (!pud_present(*pud)) {
step_forward(pvmw, PUD_SIZE);
continue;
}
pvmw->pmd = pmd_offset(pud, pvmw->address);
/*
* Make sure the pmd value isn't cached in a register by the
* compiler and used as a stale value after we've observed a
* subsequent update.
*/
pmde = READ_ONCE(*pvmw->pmd);
if (pmd_trans_huge(pmde) || is_pmd_migration_entry(pmde) ||
(pmd_present(pmde) && pmd_devmap(pmde))) {
pvmw->ptl = pmd_lock(mm, pvmw->pmd);
pmde = *pvmw->pmd;
if (!pmd_present(pmde)) {
swp_entry_t entry;
if (!thp_migration_supported() ||
!(pvmw->flags & PVMW_MIGRATION))
return not_found(pvmw);
entry = pmd_to_swp_entry(pmde);
if (!is_migration_entry(entry) ||
!check_pmd(swp_offset_pfn(entry), pvmw))
return not_found(pvmw);
return true;
}
if (likely(pmd_trans_huge(pmde) || pmd_devmap(pmde))) {
if (pvmw->flags & PVMW_MIGRATION)
return not_found(pvmw);
if (!check_pmd(pmd_pfn(pmde), pvmw))
return not_found(pvmw);
return true;
}
/* THP pmd was split under us: handle on pte level */
spin_unlock(pvmw->ptl);
pvmw->ptl = NULL;
} else if (!pmd_present(pmde)) {
/*
* If PVMW_SYNC, take and drop THP pmd lock so that we
* cannot return prematurely, while zap_huge_pmd() has
* cleared *pmd but not decremented compound_mapcount().
*/
if ((pvmw->flags & PVMW_SYNC) &&
transhuge_vma_suitable(vma, pvmw->address) &&
(pvmw->nr_pages >= HPAGE_PMD_NR)) {
spinlock_t *ptl = pmd_lock(mm, pvmw->pmd);
spin_unlock(ptl);
}
step_forward(pvmw, PMD_SIZE);
continue;
}
if (!map_pte(pvmw))
goto next_pte;
this_pte:
if (check_pte(pvmw))
return true;
next_pte:
do {
pvmw->address += PAGE_SIZE;
if (pvmw->address >= end)
return not_found(pvmw);
/* Did we cross page table boundary? */
if ((pvmw->address & (PMD_SIZE - PAGE_SIZE)) == 0) {
if (pvmw->ptl) {
spin_unlock(pvmw->ptl);
pvmw->ptl = NULL;
}
pte_unmap(pvmw->pte);
pvmw->pte = NULL;
goto restart;
}
pvmw->pte++;
if ((pvmw->flags & PVMW_SYNC) && !pvmw->ptl) {
pvmw->ptl = pte_lockptr(mm, pvmw->pmd);
spin_lock(pvmw->ptl);
}
} while (pte_none(*pvmw->pte));
if (!pvmw->ptl) {
pvmw->ptl = pte_lockptr(mm, pvmw->pmd);
spin_lock(pvmw->ptl);
}
goto this_pte;
} while (pvmw->address < end);
return false;
}
/**
* page_mapped_in_vma - check whether a page is really mapped in a VMA
* @page: the page to test
* @vma: the VMA to test
*
* Returns 1 if the page is mapped into the page tables of the VMA, 0
* if the page is not mapped into the page tables of this VMA. Only
* valid for normal file or anonymous VMAs.
*/
int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
{
struct page_vma_mapped_walk pvmw = {
.pfn = page_to_pfn(page),
.nr_pages = 1,
.vma = vma,
.flags = PVMW_SYNC,
};
pvmw.address = vma_address(page, vma);
if (pvmw.address == -EFAULT)
return 0;
if (!page_vma_mapped_walk(&pvmw))
return 0;
page_vma_mapped_walk_done(&pvmw);
return 1;
}