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[184.145.104.227]) by smtp.gmail.com with ESMTPSA id v66sm3103621qkd.113.2021.04.27.09.13.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 27 Apr 2021 09:13:20 -0700 (PDT) From: Peter Xu To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Nadav Amit , Miaohe Lin , Mike Rapoport , Andrea Arcangeli , Hugh Dickins , peterx@redhat.com, Jerome Glisse , Mike Kravetz , Jason Gunthorpe , Matthew Wilcox , Andrew Morton , Axel Rasmussen , "Kirill A . Shutemov" Subject: [PATCH v2 01/24] shmem/userfaultfd: Take care of UFFDIO_COPY_MODE_WP Date: Tue, 27 Apr 2021 12:12:54 -0400 Message-Id: <20210427161317.50682-2-peterx@redhat.com> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20210427161317.50682-1-peterx@redhat.com> References: <20210427161317.50682-1-peterx@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 | 27 ++++++++++++++++++++------- mm/userfaultfd.c | 2 +- 3 files changed, 24 insertions(+), 10 deletions(-) diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h index d82b6f3965885..a21eb25183d02 100644 --- a/include/linux/shmem_fs.h +++ b/include/linux/shmem_fs.h @@ -127,14 +127,15 @@ 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 26c76b13ad233..8fbf7680f044c 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -2360,7 +2360,8 @@ 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); @@ -2422,9 +2423,18 @@ 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 @@ -2482,10 +2492,12 @@ 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, @@ -2496,7 +2508,8 @@ 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 e14b3820c6a81..7adaebe222b8e 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -443,7 +443,7 @@ 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); -- 2.26.2