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Shutemov" , Hugh Dickins , Axel Rasmussen , Matthew Wilcox , Andrew Morton , Andrea Arcangeli , Nadav Amit Subject: [PATCH RFC 04/30] shmem/userfaultfd: Take care of UFFDIO_COPY_MODE_WP Date: Fri, 15 Jan 2021 12:08:41 -0500 Message-Id: <20210115170907.24498-5-peterx@redhat.com> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20210115170907.24498-1-peterx@redhat.com> References: <20210115170907.24498-1-peterx@redhat.com> MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=peterx@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com 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: Firstly, pass wp_copy into shmem_mfill_atomic_pte() through the stack. Then apply the UFFD_WP bit properly when the UFFDIO_COPY on shmem is with UFFDIO_COPY_MODE_WP. One thing to mention is that shmem_mfill_atomic_pte() needs to set the dirty bit in pte even if UFFDIO_COPY_MODE_WP is set. The reason is similar to dcf7fe9d8976 ("userfaultfd: shmem: UFFDIO_COPY: set the page dirty if VM_WRITE is not set") where we need to set page as dirty even if VM_WRITE is no there. It's just that shmem can drop the pte any time later, and if it's not dirty the data will be dropped. For uffd-wp, that could lead to data loss if without the dirty bit set. Note that shmem_mfill_zeropage_pte() will always call shmem_mfill_atomic_pte() with wp_copy==false because UFFDIO_ZEROCOPY does not support UFFDIO_COPY_MODE_WP. Signed-off-by: Peter Xu --- include/linux/shmem_fs.h | 5 +++-- mm/shmem.c | 26 +++++++++++++++++++------- mm/userfaultfd.c | 2 +- 3 files changed, 23 insertions(+), 10 deletions(-) diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h index a5a5d1d4d7b1..9d6fc68a1e57 100644 --- a/include/linux/shmem_fs.h +++ b/include/linux/shmem_fs.h @@ -123,14 +123,15 @@ extern int shmem_mcopy_atomic_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd, struct vm_area_struct *dst_vma, unsigned long dst_addr, unsigned long src_addr, - struct page **pagep); + struct page **pagep, + bool wp_copy); extern int shmem_mfill_zeropage_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd, struct vm_area_struct *dst_vma, unsigned long dst_addr); #else #define shmem_mcopy_atomic_pte(dst_mm, dst_pte, dst_vma, dst_addr, \ - src_addr, pagep) ({ BUG(); 0; }) + src_addr, pagep, wp_copy) ({ BUG(); 0; }) #define shmem_mfill_zeropage_pte(dst_mm, dst_pmd, dst_vma, \ dst_addr) ({ BUG(); 0; }) #endif diff --git a/mm/shmem.c b/mm/shmem.c index 537c137698f8..de45333626f7 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -2363,7 +2363,8 @@ static int shmem_mfill_atomic_pte(struct mm_struct *dst_mm, unsigned long dst_addr, unsigned long src_addr, bool zeropage, - struct page **pagep) + struct page **pagep, + bool wp_copy) { struct inode *inode = file_inode(dst_vma->vm_file); struct shmem_inode_info *info = SHMEM_I(inode); @@ -2425,9 +2426,18 @@ static int shmem_mfill_atomic_pte(struct mm_struct *dst_mm, goto out_release; _dst_pte = mk_pte(page, dst_vma->vm_page_prot); - if (dst_vma->vm_flags & VM_WRITE) - _dst_pte = pte_mkwrite(pte_mkdirty(_dst_pte)); - else { + if (dst_vma->vm_flags & VM_WRITE) { + if (wp_copy) + _dst_pte = pte_mkuffd_wp(pte_wrprotect(_dst_pte)); + else + _dst_pte = pte_mkwrite(_dst_pte); + /* + * Similar reason to set_page_dirty(), that we need to mark the + * pte dirty even if wp_copy==true here, otherwise the pte and + * its page could be dropped at anytime when e.g. swapped out. + */ + _dst_pte = pte_mkdirty(_dst_pte); + } else { /* * We don't set the pte dirty if the vma has no * VM_WRITE permission, so mark the page dirty or it @@ -2485,10 +2495,12 @@ int shmem_mcopy_atomic_pte(struct mm_struct *dst_mm, struct vm_area_struct *dst_vma, unsigned long dst_addr, unsigned long src_addr, - struct page **pagep) + struct page **pagep, + bool wp_copy) { return shmem_mfill_atomic_pte(dst_mm, dst_pmd, dst_vma, - dst_addr, src_addr, false, pagep); + dst_addr, src_addr, false, pagep, + wp_copy); } int shmem_mfill_zeropage_pte(struct mm_struct *dst_mm, @@ -2499,7 +2511,7 @@ int shmem_mfill_zeropage_pte(struct mm_struct *dst_mm, struct page *page = NULL; return shmem_mfill_atomic_pte(dst_mm, dst_pmd, dst_vma, - dst_addr, 0, true, &page); + dst_addr, 0, true, &page, false); } #ifdef CONFIG_TMPFS diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 9a3d451402d7..6d4b3b7c7f9f 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -445,7 +445,7 @@ static __always_inline ssize_t mfill_atomic_pte(struct mm_struct *dst_mm, if (!zeropage) err = shmem_mcopy_atomic_pte(dst_mm, dst_pmd, dst_vma, dst_addr, - src_addr, page); + src_addr, page, wp_copy); else err = shmem_mfill_zeropage_pte(dst_mm, dst_pmd, dst_vma, dst_addr);