The patch introduces new interface to check if a page is mapped into a vma.
It aims to address shortcomings of page_check_address{,_transhuge}.Existing interface is not able to handle PTE-mapped THPs: it only finds the first PTE. The rest lefted unnoticed. page_vma_mapped_walk() iterates over all possible mapping of the page in the vma. Signed-off-by: Kirill A. Shutemov <[email protected]> --- include/linux/rmap.h | 26 +++++++ mm/Makefile | 6 +- mm/huge_memory.c | 9 ++- mm/page_vma_mapped.c | 188 +++++++++++++++++++++++++++++++++++++++++++++++++++ 4 files changed, 224 insertions(+), 5 deletions(-) create mode 100644 mm/page_vma_mapped.c diff --git a/include/linux/rmap.h b/include/linux/rmap.h index 15321fb1df6b..b76343610653 100644 --- a/include/linux/rmap.h +++ b/include/linux/rmap.h @@ -9,6 +9,7 @@ #include <linux/mm.h> #include <linux/rwsem.h> #include <linux/memcontrol.h> +#include <linux/highmem.h> /* * The anon_vma heads a list of private "related" vmas, to scan if @@ -232,6 +233,31 @@ static inline bool page_check_address_transhuge(struct page *page, } #endif +/* Avoid racy checks */ +#define PVMW_SYNC (1 << 0) +/* Look for migarion entries rather than present PTEs */ +#define PVMW_MIGRATION (1 << 1) + +struct page_vma_mapped_walk { + struct page *page; + struct vm_area_struct *vma; + unsigned long address; + pmd_t *pmd; + pte_t *pte; + spinlock_t *ptl; + unsigned int flags; +}; + +static inline void page_vma_mapped_walk_done(struct page_vma_mapped_walk *pvmw) +{ + if (pvmw->pte) + pte_unmap(pvmw->pte); + if (pvmw->ptl) + spin_unlock(pvmw->ptl); +} + +bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw); + /* * Used by swapoff to help locate where page is expected in vma. */ diff --git a/mm/Makefile b/mm/Makefile index 295bd7a9f76b..e375745a88a5 100644 --- a/mm/Makefile +++ b/mm/Makefile @@ -23,8 +23,10 @@ KCOV_INSTRUMENT_vmstat.o := n mmu-y := nommu.o mmu-$(CONFIG_MMU) := gup.o highmem.o memory.o mincore.o \ - mlock.o mmap.o mprotect.o mremap.o msync.o rmap.o \ - vmalloc.o pagewalk.o pgtable-generic.o + mlock.o mmap.o mprotect.o mremap.o msync.o \ + page_vma_mapped.o pagewalk.o pgtable-generic.o \ + rmap.o vmalloc.o + ifdef CONFIG_CROSS_MEMORY_ATTACH mmu-$(CONFIG_MMU) += process_vm_access.o diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 9a6bd6c8d55a..16820e001d79 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1862,9 +1862,12 @@ static void freeze_page(struct page *page) static void unfreeze_page(struct page *page) { int i; - - for (i = 0; i < HPAGE_PMD_NR; i++) - remove_migration_ptes(page + i, page + i, true); + if (PageTransHuge(page)) { + remove_migration_ptes(page, page, true); + } else { + for (i = 0; i < HPAGE_PMD_NR; i++) + remove_migration_ptes(page + i, page + i, true); + } } static void __split_huge_page_tail(struct page *head, int tail, diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c new file mode 100644 index 000000000000..bbd2a39e985d --- /dev/null +++ b/mm/page_vma_mapped.c @@ -0,0 +1,188 @@ +#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 check_pmd(struct page_vma_mapped_walk *pvmw) +{ + pmd_t pmde; + /* + * Make sure we don't re-load pmd between present and !trans_huge check. + * We need a consistent view. + */ + pmde = READ_ONCE(*pvmw->pmd); + return pmd_present(pmde) && !pmd_trans_huge(pmde); +} + +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 { + if (!pte_present(*pvmw->pte)) + return false; + } + } + pvmw->ptl = pte_lockptr(pvmw->vma->vm_mm, pvmw->pmd); + spin_lock(pvmw->ptl); + return true; +} + +static bool check_pte(struct page_vma_mapped_walk *pvmw) +{ + if (pvmw->flags & PVMW_MIGRATION) { +#ifdef CONFIG_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)) + return false; + if (migration_entry_to_page(entry) - pvmw->page >= + hpage_nr_pages(pvmw->page)) { + return false; + } + if (migration_entry_to_page(entry) < pvmw->page) + return false; +#else + WARN_ON_ONCE(1); +#endif + } else { + if (!pte_present(*pvmw->pte)) + return false; + + /* THP can be referenced by any subpage */ + if (pte_page(*pvmw->pte) - pvmw->page >= + hpage_nr_pages(pvmw->page)) { + return false; + } + if (pte_page(*pvmw->pte) < pvmw->page) + return false; + } + + return true; +} + +/** + * page_vma_mapped_walk - check if @pvmw->page 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. + * + * Retruns 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 mm_struct *mm = pvmw->vma->vm_mm; + struct page *page = pvmw->page; + pgd_t *pgd; + pud_t *pud; + + /* The only possible pmd mapping has been handled on last iteration */ + if (pvmw->pmd && !pvmw->pte) + return not_found(pvmw); + + /* Only for THP, seek to next pte entry makes sense */ + if (pvmw->pte) { + if (!PageTransHuge(pvmw->page) || PageHuge(pvmw->page)) + return not_found(pvmw); + goto next_pte; + } + + if (unlikely(PageHuge(pvmw->page))) { + /* when pud is not present, pte will be NULL */ + pvmw->pte = huge_pte_offset(mm, pvmw->address); + if (!pvmw->pte) + return false; + + pvmw->ptl = huge_pte_lockptr(page_hstate(page), mm, pvmw->pte); + spin_lock(pvmw->ptl); + if (!check_pte(pvmw)) + return not_found(pvmw); + return true; + } +restart: + pgd = pgd_offset(mm, pvmw->address); + if (!pgd_present(*pgd)) + return false; + pud = pud_offset(pgd, pvmw->address); + if (!pud_present(*pud)) + return false; + pvmw->pmd = pmd_offset(pud, pvmw->address); + if (pmd_trans_huge(*pvmw->pmd)) { + pvmw->ptl = pmd_lock(mm, pvmw->pmd); + if (!pmd_present(*pvmw->pmd)) + return not_found(pvmw); + if (likely(pmd_trans_huge(*pvmw->pmd))) { + if (pvmw->flags & PVMW_MIGRATION) + return not_found(pvmw); + if (pmd_page(*pvmw->pmd) != page) + return not_found(pvmw); + return true; + } else { + /* THP pmd was split under us: handle on pte level */ + spin_unlock(pvmw->ptl); + pvmw->ptl = NULL; + } + } else { + if (!check_pmd(pvmw)) + return false; + } + if (!map_pte(pvmw)) + goto next_pte; + while (1) { + if (check_pte(pvmw)) + return true; +next_pte: do { + pvmw->address += PAGE_SIZE; + if (pvmw->address >= + __vma_address(pvmw->page, pvmw->vma) + + hpage_nr_pages(pvmw->page) * PAGE_SIZE) + return not_found(pvmw); + /* Did we cross page table boundary? */ + if (pvmw->address % PMD_SIZE == 0) { + pte_unmap(pvmw->pte); + if (pvmw->ptl) { + spin_unlock(pvmw->ptl); + pvmw->ptl = NULL; + } + goto restart; + } else { + pvmw->pte++; + } + } while (pte_none(*pvmw->pte)); + + if (!pvmw->ptl) { + pvmw->ptl = pte_lockptr(mm, pvmw->pmd); + spin_lock(pvmw->ptl); + } + } +} -- 2.11.0
