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Shutemov" Subject: [PATCH v3 2/7] mm: Add a walk_page_mapping() function to the pagewalk code Date: Wed, 2 Oct 2019 15:47:25 +0200 Message-Id: <20191002134730.40985-3-thomas_os@shipmail.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20191002134730.40985-1-thomas_os@shipmail.org> References: <20191002134730.40985-1-thomas_os@shipmail.org> MIME-Version: 1.0 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: Thomas Hellstrom For users that want to travers all page table entries pointing into a region of a struct address_space mapping, introduce a walk_page_mapping() function. The walk_page_mapping() function will be initially be used for dirty- tracking in virtual graphics drivers. Cc: Andrew Morton Cc: Matthew Wilcox Cc: Will Deacon Cc: Peter Zijlstra Cc: Rik van Riel Cc: Minchan Kim Cc: Michal Hocko Cc: Huang Ying Cc: Jérôme Glisse Cc: Kirill A. Shutemov Signed-off-by: Thomas Hellstrom --- include/linux/pagewalk.h | 9 ++++ mm/pagewalk.c | 99 +++++++++++++++++++++++++++++++++++++++- 2 files changed, 107 insertions(+), 1 deletion(-) diff --git a/include/linux/pagewalk.h b/include/linux/pagewalk.h index bddd9759bab9..6ec82e92c87f 100644 --- a/include/linux/pagewalk.h +++ b/include/linux/pagewalk.h @@ -24,6 +24,9 @@ struct mm_walk; * "do page table walk over the current vma", returning * a negative value means "abort current page table walk * right now" and returning 1 means "skip the current vma" + * @pre_vma: if set, called before starting walk on a non-null vma. + * @post_vma: if set, called after a walk on a non-null vma, provided + * that @pre_vma and the vma walk succeeded. */ struct mm_walk_ops { int (*pud_entry)(pud_t *pud, unsigned long addr, @@ -39,6 +42,9 @@ struct mm_walk_ops { struct mm_walk *walk); int (*test_walk)(unsigned long addr, unsigned long next, struct mm_walk *walk); + int (*pre_vma)(unsigned long start, unsigned long end, + struct mm_walk *walk); + void (*post_vma)(struct mm_walk *walk); }; /** @@ -62,5 +68,8 @@ int walk_page_range(struct mm_struct *mm, unsigned long start, void *private); int walk_page_vma(struct vm_area_struct *vma, const struct mm_walk_ops *ops, void *private); +int walk_page_mapping(struct address_space *mapping, pgoff_t first_index, + pgoff_t nr, const struct mm_walk_ops *ops, + void *private); #endif /* _LINUX_PAGEWALK_H */ diff --git a/mm/pagewalk.c b/mm/pagewalk.c index d48c2a986ea3..658d1e5ec428 100644 --- a/mm/pagewalk.c +++ b/mm/pagewalk.c @@ -253,13 +253,23 @@ static int __walk_page_range(unsigned long start, unsigned long end, { int err = 0; struct vm_area_struct *vma = walk->vma; + const struct mm_walk_ops *ops = walk->ops; + + if (vma && ops->pre_vma) { + err = ops->pre_vma(start, end, walk); + if (err) + return err; + } if (vma && is_vm_hugetlb_page(vma)) { - if (walk->ops->hugetlb_entry) + if (ops->hugetlb_entry) err = walk_hugetlb_range(start, end, walk); } else err = walk_pgd_range(start, end, walk); + if (vma && ops->post_vma) + ops->post_vma(walk); + return err; } @@ -285,11 +295,17 @@ static int __walk_page_range(unsigned long start, unsigned long end, * - <0 : failed to handle the current entry, and return to the caller * with error code. * + * * Before starting to walk page table, some callers want to check whether * they really want to walk over the current vma, typically by checking * its vm_flags. walk_page_test() and @ops->test_walk() are used for this * purpose. * + * If operations need to be staged before and committed after a vma is walked, + * there are two callbacks, pre_vma() and post_vma(). Note that post_vma(), + * since it is intended to handle commit-type operations, can't return any + * errors. + * * struct mm_walk keeps current values of some common data like vma and pmd, * which are useful for the access from callbacks. If you want to pass some * caller-specific data to callbacks, @private should be helpful. @@ -376,3 +392,84 @@ int walk_page_vma(struct vm_area_struct *vma, const struct mm_walk_ops *ops, return err; return __walk_page_range(vma->vm_start, vma->vm_end, &walk); } + +/** + * walk_page_mapping - walk all memory areas mapped into a struct address_space. + * @mapping: Pointer to the struct address_space + * @first_index: First page offset in the address_space + * @nr: Number of incremental page offsets to cover + * @ops: operation to call during the walk + * @private: private data for callbacks' usage + * + * This function walks all memory areas mapped into a struct address_space. + * The walk is limited to only the given page-size index range, but if + * the index boundaries cross a huge page-table entry, that entry will be + * included. + * + * Also see walk_page_range() for additional information. + * + * Locking: + * This function can't require that the struct mm_struct::mmap_sem is held, + * since @mapping may be mapped by multiple processes. Instead + * @mapping->i_mmap_rwsem must be held. This might have implications in the + * callbacks, and it's up tho the caller to ensure that the + * struct mm_struct::mmap_sem is not needed. + * + * Also this means that a caller can't rely on the struct + * vm_area_struct::vm_flags to be constant across a call, + * except for immutable flags. Callers requiring this shouldn't use + * this function. + * + * If @mapping allows faulting of huge pmds and puds, it is desirable + * that its huge_fault() handler blocks while this function is running on + * @mapping. Otherwise a race may occur where the huge entry is split when + * it was intended to be handled in a huge entry callback. This requires an + * external lock, for example that @mapping->i_mmap_rwsem is held in + * write mode in the huge_fault() handlers. + */ +int walk_page_mapping(struct address_space *mapping, pgoff_t first_index, + pgoff_t nr, const struct mm_walk_ops *ops, + void *private) +{ + struct mm_walk walk = { + .ops = ops, + .private = private, + }; + struct vm_area_struct *vma; + pgoff_t vba, vea, cba, cea; + unsigned long start_addr, end_addr; + int err = 0; + + lockdep_assert_held(&mapping->i_mmap_rwsem); + vma_interval_tree_foreach(vma, &mapping->i_mmap, first_index, + first_index + nr - 1) { + /* Clip to the vma */ + vba = vma->vm_pgoff; + vea = vba + vma_pages(vma); + cba = first_index; + cba = max(cba, vba); + cea = first_index + nr; + cea = min(cea, vea); + + start_addr = ((cba - vba) << PAGE_SHIFT) + vma->vm_start; + end_addr = ((cea - vba) << PAGE_SHIFT) + vma->vm_start; + if (start_addr >= end_addr) + continue; + + walk.vma = vma; + walk.mm = vma->vm_mm; + + err = walk_page_test(vma->vm_start, vma->vm_end, &walk); + if (err > 0) { + err = 0; + break; + } else if (err < 0) + break; + + err = __walk_page_range(start_addr, end_addr, &walk); + if (err) + break; + } + + return err; +}