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[184.144.111.238]) by smtp.gmail.com with ESMTPSA id b25sm1625854qka.123.2021.07.14.15.21.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 14 Jul 2021 15:21:37 -0700 (PDT) From: Peter Xu To: linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: Jason Gunthorpe , peterx@redhat.com, Matthew Wilcox , Andrew Morton , Axel Rasmussen , Nadav Amit , Jerome Glisse , Mike Rapoport , Miaohe Lin , Hugh Dickins , Alistair Popple , Andrea Arcangeli , Mike Kravetz , "Kirill A . Shutemov" , David Hildenbrand Subject: [PATCH v4 10/26] shmem/userfaultfd: Persist uffd-wp bit across zapping for file-backed Date: Wed, 14 Jul 2021 18:21:01 -0400 Message-Id: <20210714222117.47648-11-peterx@redhat.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210714222117.47648-1-peterx@redhat.com> References: <20210714222117.47648-1-peterx@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org File-backed memory is prone to being unmapped at any time. It means all information in the pte will be dropped, including the uffd-wp flag. Since the uffd-wp info cannot be stored in page cache or swap cache, persist this wr-protect information by installing the special uffd-wp marker pte when we're going to unmap a uffd wr-protected pte. When the pte is accessed again, we will know it's previously wr-protected by recognizing the special pte. Meanwhile add a new flag ZAP_FLAG_DROP_FILE_UFFD_WP when we don't want to persist such an information. For example, when destroying the whole vma, or punching a hole in a shmem file. For the latter, we can only drop the uffd-wp bit when holding the page lock. It means the unmap_mapping_range() in shmem_fallocate() still reuqires to zap without ZAP_FLAG_DROP_FILE_UFFD_WP because that's still racy with the page faults. Signed-off-by: Peter Xu --- include/linux/mm.h | 11 +++++++++ include/linux/mm_inline.h | 42 +++++++++++++++++++++++++++++++++ mm/memory.c | 49 +++++++++++++++++++++++++++++++++++++-- mm/rmap.c | 8 +++++++ 4 files changed, 108 insertions(+), 2 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 62a75e4414e3..8de230fc7b84 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1719,6 +1719,8 @@ extern void user_shm_unlock(size_t, struct ucounts *); #define ZAP_FLAG_CHECK_MAPPING BIT(0) /* Whether to skip zapping swap entries */ #define ZAP_FLAG_SKIP_SWAP BIT(1) +/* Whether to completely drop uffd-wp entries for file-backed memory */ +#define ZAP_FLAG_DROP_FILE_UFFD_WP BIT(2) /* * Parameter block passed down to zap_pte_range in exceptional cases. @@ -1752,6 +1754,15 @@ zap_skip_swap(struct zap_details *details) return details->zap_flags & ZAP_FLAG_SKIP_SWAP; } +static inline bool +zap_drop_file_uffd_wp(struct zap_details *details) +{ + if (!details) + return false; + + return details->zap_flags & ZAP_FLAG_DROP_FILE_UFFD_WP; +} + struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, pte_t pte); struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr, diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h index 355ea1ee32bd..95556b4bfe7a 100644 --- a/include/linux/mm_inline.h +++ b/include/linux/mm_inline.h @@ -4,6 +4,8 @@ #include #include +#include +#include /** * page_is_file_lru - should the page be on a file LRU or anon LRU? @@ -104,4 +106,44 @@ static __always_inline void del_page_from_lru_list(struct page *page, update_lru_size(lruvec, page_lru(page), page_zonenum(page), -thp_nr_pages(page)); } + +/* + * If this pte is wr-protected by uffd-wp in any form, arm the special pte to + * replace a none pte. NOTE! This should only be called when *pte is already + * cleared so we will never accidentally replace something valuable. Meanwhile + * none pte also means we are not demoting the pte so tlb flushed is not needed. + * E.g., when pte cleared the caller should have taken care of the tlb flush. + * + * Must be called with pgtable lock held. + */ +static inline void +pte_install_uffd_wp_if_needed(struct vm_area_struct *vma, unsigned long addr, + pte_t *pte, pte_t pteval) +{ +#ifdef CONFIG_USERFAULTFD + bool arm_uffd_pte = false; + + /* The current status of the pte should be "cleared" before calling */ + WARN_ON_ONCE(!pte_none(*pte)); + + if (vma_is_anonymous(vma)) + return; + + /* A uffd-wp wr-protected normal pte */ + if (unlikely(pte_present(pteval) && pte_uffd_wp(pteval))) + arm_uffd_pte = true; + + /* + * A uffd-wp wr-protected swap pte. Note: this should even work for + * pte_swp_uffd_wp_special() too. + */ + if (unlikely(is_swap_pte(pteval) && pte_swp_uffd_wp(pteval))) + arm_uffd_pte = true; + + if (unlikely(arm_uffd_pte)) + set_pte_at(vma->vm_mm, addr, pte, + pte_swp_mkuffd_wp_special(vma)); +#endif +} + #endif diff --git a/mm/memory.c b/mm/memory.c index d6b1adbf29e4..223781f115e9 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -73,6 +73,7 @@ #include #include #include +#include #include @@ -1301,6 +1302,21 @@ copy_page_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma) return ret; } +/* + * This function makes sure that we'll replace the none pte with an uffd-wp + * swap special pte marker when necessary. Must be with the pgtable lock held. + */ +static inline void +zap_install_uffd_wp_if_needed(struct vm_area_struct *vma, + unsigned long addr, pte_t *pte, + struct zap_details *details, pte_t pteval) +{ + if (zap_drop_file_uffd_wp(details)) + return; + + pte_install_uffd_wp_if_needed(vma, addr, pte, pteval); +} + static unsigned long zap_pte_range(struct mmu_gather *tlb, struct vm_area_struct *vma, pmd_t *pmd, unsigned long addr, unsigned long end, @@ -1338,6 +1354,8 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb, ptent = ptep_get_and_clear_full(mm, addr, pte, tlb->fullmm); tlb_remove_tlb_entry(tlb, pte, addr); + zap_install_uffd_wp_if_needed(vma, addr, pte, details, + ptent); if (unlikely(!page)) continue; @@ -1362,6 +1380,22 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb, continue; } + /* + * If this is a special uffd-wp marker pte... Drop it only if + * enforced to do so. + */ + if (unlikely(is_swap_special_pte(ptent))) { + WARN_ON_ONCE(!pte_swp_uffd_wp_special(ptent)); + /* + * If this is a common unmap of ptes, keep this as is. + * Drop it only if this is a whole-vma destruction. + */ + if (zap_drop_file_uffd_wp(details)) + ptep_get_and_clear_full(mm, addr, pte, + tlb->fullmm); + continue; + } + entry = pte_to_swp_entry(ptent); if (is_device_private_entry(entry) || is_device_exclusive_entry(entry)) { @@ -1369,6 +1403,13 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb, if (unlikely(zap_skip_check_mapping(details, page))) continue; + /* + * Both device private/exclusive mappings should only + * work with anonymous page so far, so we don't need to + * consider uffd-wp bit when zap. For more information, + * see zap_install_uffd_wp_if_needed(). + */ + WARN_ON_ONCE(!vma_is_anonymous(vma)); pte_clear_not_present_full(mm, addr, pte, tlb->fullmm); rss[mm_counter(page)]--; @@ -1393,6 +1434,7 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb, if (unlikely(!free_swap_and_cache(entry))) print_bad_pte(vma, addr, ptent, NULL); pte_clear_not_present_full(mm, addr, pte, tlb->fullmm); + zap_install_uffd_wp_if_needed(vma, addr, pte, details, ptent); } while (pte++, addr += PAGE_SIZE, addr != end); add_mm_rss_vec(mm, rss); @@ -1603,12 +1645,15 @@ void unmap_vmas(struct mmu_gather *tlb, unsigned long end_addr) { struct mmu_notifier_range range; + struct zap_details details = { + .zap_flags = ZAP_FLAG_DROP_FILE_UFFD_WP, + }; mmu_notifier_range_init(&range, MMU_NOTIFY_UNMAP, 0, vma, vma->vm_mm, start_addr, end_addr); mmu_notifier_invalidate_range_start(&range); for ( ; vma && vma->vm_start < end_addr; vma = vma->vm_next) - unmap_single_vma(tlb, vma, start_addr, end_addr, NULL); + unmap_single_vma(tlb, vma, start_addr, end_addr, &details); mmu_notifier_invalidate_range_end(&range); } @@ -3353,7 +3398,7 @@ void unmap_mapping_page(struct page *page) details.zap_mapping = mapping; details.single_page = page; - details.zap_flags = ZAP_FLAG_CHECK_MAPPING; + details.zap_flags = ZAP_FLAG_CHECK_MAPPING | ZAP_FLAG_DROP_FILE_UFFD_WP; i_mmap_lock_write(mapping); if (unlikely(!RB_EMPTY_ROOT(&mapping->i_mmap.rb_root))) diff --git a/mm/rmap.c b/mm/rmap.c index 795f9d5f8386..92ba81567089 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -72,6 +72,7 @@ #include #include #include +#include #include @@ -1515,6 +1516,13 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma, pteval = ptep_clear_flush(vma, address, pvmw.pte); } + /* + * Now the pte is cleared. If this is uffd-wp armed pte, we + * may want to replace a none pte with a marker pte if it's + * file-backed, so we don't lose the tracking information. + */ + pte_install_uffd_wp_if_needed(vma, address, pvmw.pte, pteval); + /* Move the dirty bit to the page. Now the pte is gone. */ if (pte_dirty(pteval)) set_page_dirty(page); -- 2.31.1