userfaultfd/shmem: support UFFDIO_CONTINUE for shmem
With this change, userspace can resolve a minor fault within a shmem-backed area with a UFFDIO_CONTINUE ioctl. The semantics for this match those for hugetlbfs - we look up the existing page in the page cache, and install a PTE for it. This commit introduces a new helper: mfill_atomic_install_pte. Why handle UFFDIO_CONTINUE for shmem in mm/userfaultfd.c, instead of in shmem.c? The existing userfault implementation only relies on shmem.c for VM_SHARED VMAs. However, minor fault handling / CONTINUE work just fine for !VM_SHARED VMAs as well. We'd prefer to handle CONTINUE for shmem in one place, regardless of shared/private (to reduce code duplication). Why add a new mfill_atomic_install_pte helper? A problem we have with continue is that shmem_mfill_atomic_pte() and mcopy_atomic_pte() are *close* to what we want, but not exactly. We do want to setup the PTEs in a CONTINUE operation, but we don't want to e.g. allocate a new page, charge it (e.g. to the shmem inode), manipulate various flags, etc. Also we have the problem stated above: shmem_mfill_atomic_pte() and mcopy_atomic_pte() both handle one-half of the problem (shared / private) continue cares about. So, introduce mcontinue_atomic_pte(), to handle all of the shmem continue cases. Introduce the helper so it doesn't duplicate code with mcopy_atomic_pte(). In a future commit, shmem_mfill_atomic_pte() will also be modified to use this new helper. However, since this is a bigger refactor, it seems most clear to do it as a separate change. Link: https://lkml.kernel.org/r/20210503180737.2487560-5-axelrasmussen@google.com Signed-off-by: Axel Rasmussen <axelrasmussen@google.com> Acked-by: Hugh Dickins <hughd@google.com> Acked-by: Peter Xu <peterx@redhat.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Brian Geffon <bgeffon@google.com> Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com> Cc: Jerome Glisse <jglisse@redhat.com> Cc: Joe Perches <joe@perches.com> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Lokesh Gidra <lokeshgidra@google.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Mike Rapoport <rppt@linux.vnet.ibm.com> Cc: Mina Almasry <almasrymina@google.com> Cc: Oliver Upton <oupton@google.com> Cc: Shaohua Li <shli@fb.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Stephen Rothwell <sfr@canb.auug.org.au> Cc: Wang Qing <wangqing@vivo.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Axel Rasmussen
Linus Torvalds
Родитель
c949b097ef
Коммит
153132571f
172
mm/userfaultfd.c
172
mm/userfaultfd.c
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@ -48,6 +48,83 @@ struct vm_area_struct *find_dst_vma(struct mm_struct *dst_mm,
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return dst_vma;
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}
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/*
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* Install PTEs, to map dst_addr (within dst_vma) to page.
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*
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* This function handles MCOPY_ATOMIC_CONTINUE (which is always file-backed),
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* whether or not dst_vma is VM_SHARED. It also handles the more general
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* MCOPY_ATOMIC_NORMAL case, when dst_vma is *not* VM_SHARED (it may be file
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* backed, or not).
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*
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* Note that MCOPY_ATOMIC_NORMAL for a VM_SHARED dst_vma is handled by
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* shmem_mcopy_atomic_pte instead.
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*/
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static int mfill_atomic_install_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd,
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struct vm_area_struct *dst_vma,
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unsigned long dst_addr, struct page *page,
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bool newly_allocated, bool wp_copy)
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{
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int ret;
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pte_t _dst_pte, *dst_pte;
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bool writable = dst_vma->vm_flags & VM_WRITE;
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bool vm_shared = dst_vma->vm_flags & VM_SHARED;
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bool page_in_cache = page->mapping;
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spinlock_t *ptl;
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struct inode *inode;
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pgoff_t offset, max_off;
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_dst_pte = mk_pte(page, dst_vma->vm_page_prot);
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if (page_in_cache && !vm_shared)
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writable = false;
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if (writable || !page_in_cache)
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_dst_pte = pte_mkdirty(_dst_pte);
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if (writable) {
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if (wp_copy)
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_dst_pte = pte_mkuffd_wp(_dst_pte);
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else
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_dst_pte = pte_mkwrite(_dst_pte);
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}
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dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
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if (vma_is_shmem(dst_vma)) {
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/* serialize against truncate with the page table lock */
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inode = dst_vma->vm_file->f_inode;
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offset = linear_page_index(dst_vma, dst_addr);
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max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
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ret = -EFAULT;
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if (unlikely(offset >= max_off))
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goto out_unlock;
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}
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ret = -EEXIST;
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if (!pte_none(*dst_pte))
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goto out_unlock;
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if (page_in_cache)
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page_add_file_rmap(page, false);
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else
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page_add_new_anon_rmap(page, dst_vma, dst_addr, false);
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/*
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* Must happen after rmap, as mm_counter() checks mapping (via
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* PageAnon()), which is set by __page_set_anon_rmap().
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*/
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inc_mm_counter(dst_mm, mm_counter(page));
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if (newly_allocated)
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lru_cache_add_inactive_or_unevictable(page, dst_vma);
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set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
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/* No need to invalidate - it was non-present before */
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update_mmu_cache(dst_vma, dst_addr, dst_pte);
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ret = 0;
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out_unlock:
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pte_unmap_unlock(dst_pte, ptl);
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return ret;
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}
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static int mcopy_atomic_pte(struct mm_struct *dst_mm,
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pmd_t *dst_pmd,
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struct vm_area_struct *dst_vma,
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@ -56,13 +133,9 @@ static int mcopy_atomic_pte(struct mm_struct *dst_mm,
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struct page **pagep,
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bool wp_copy)
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{
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pte_t _dst_pte, *dst_pte;
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spinlock_t *ptl;
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void *page_kaddr;
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int ret;
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struct page *page;
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pgoff_t offset, max_off;
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struct inode *inode;
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if (!*pagep) {
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ret = -ENOMEM;
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@ -99,43 +172,12 @@ static int mcopy_atomic_pte(struct mm_struct *dst_mm,
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if (mem_cgroup_charge(page, dst_mm, GFP_KERNEL))
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goto out_release;
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_dst_pte = pte_mkdirty(mk_pte(page, dst_vma->vm_page_prot));
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if (dst_vma->vm_flags & VM_WRITE) {
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if (wp_copy)
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_dst_pte = pte_mkuffd_wp(_dst_pte);
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else
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_dst_pte = pte_mkwrite(_dst_pte);
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}
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dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
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if (dst_vma->vm_file) {
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/* the shmem MAP_PRIVATE case requires checking the i_size */
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inode = dst_vma->vm_file->f_inode;
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offset = linear_page_index(dst_vma, dst_addr);
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max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
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ret = -EFAULT;
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if (unlikely(offset >= max_off))
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goto out_release_uncharge_unlock;
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}
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ret = -EEXIST;
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if (!pte_none(*dst_pte))
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goto out_release_uncharge_unlock;
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inc_mm_counter(dst_mm, MM_ANONPAGES);
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page_add_new_anon_rmap(page, dst_vma, dst_addr, false);
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lru_cache_add_inactive_or_unevictable(page, dst_vma);
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set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
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/* No need to invalidate - it was non-present before */
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update_mmu_cache(dst_vma, dst_addr, dst_pte);
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pte_unmap_unlock(dst_pte, ptl);
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ret = 0;
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ret = mfill_atomic_install_pte(dst_mm, dst_pmd, dst_vma, dst_addr,
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page, true, wp_copy);
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if (ret)
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goto out_release;
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out:
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return ret;
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out_release_uncharge_unlock:
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pte_unmap_unlock(dst_pte, ptl);
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out_release:
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put_page(page);
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goto out;
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@ -176,6 +218,41 @@ out_unlock:
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return ret;
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}
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/* Handles UFFDIO_CONTINUE for all shmem VMAs (shared or private). */
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static int mcontinue_atomic_pte(struct mm_struct *dst_mm,
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pmd_t *dst_pmd,
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struct vm_area_struct *dst_vma,
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unsigned long dst_addr,
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bool wp_copy)
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{
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struct inode *inode = file_inode(dst_vma->vm_file);
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pgoff_t pgoff = linear_page_index(dst_vma, dst_addr);
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struct page *page;
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int ret;
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ret = shmem_getpage(inode, pgoff, &page, SGP_READ);
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if (ret)
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goto out;
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if (!page) {
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ret = -EFAULT;
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goto out;
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}
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ret = mfill_atomic_install_pte(dst_mm, dst_pmd, dst_vma, dst_addr,
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page, false, wp_copy);
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if (ret)
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goto out_release;
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unlock_page(page);
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ret = 0;
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out:
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return ret;
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out_release:
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unlock_page(page);
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put_page(page);
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goto out;
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}
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static pmd_t *mm_alloc_pmd(struct mm_struct *mm, unsigned long address)
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{
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pgd_t *pgd;
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@ -367,11 +444,16 @@ static __always_inline ssize_t mfill_atomic_pte(struct mm_struct *dst_mm,
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unsigned long dst_addr,
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unsigned long src_addr,
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struct page **page,
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bool zeropage,
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enum mcopy_atomic_mode mode,
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bool wp_copy)
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{
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ssize_t err;
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if (mode == MCOPY_ATOMIC_CONTINUE) {
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return mcontinue_atomic_pte(dst_mm, dst_pmd, dst_vma, dst_addr,
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wp_copy);
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}
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/*
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* The normal page fault path for a shmem will invoke the
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* fault, fill the hole in the file and COW it right away. The
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@ -383,7 +465,7 @@ static __always_inline ssize_t mfill_atomic_pte(struct mm_struct *dst_mm,
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* and not in the radix tree.
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*/
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if (!(dst_vma->vm_flags & VM_SHARED)) {
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if (!zeropage)
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if (mode == MCOPY_ATOMIC_NORMAL)
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err = mcopy_atomic_pte(dst_mm, dst_pmd, dst_vma,
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dst_addr, src_addr, page,
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wp_copy);
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@ -393,7 +475,8 @@ static __always_inline ssize_t mfill_atomic_pte(struct mm_struct *dst_mm,
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} else {
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VM_WARN_ON_ONCE(wp_copy);
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err = shmem_mfill_atomic_pte(dst_mm, dst_pmd, dst_vma,
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dst_addr, src_addr, zeropage,
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dst_addr, src_addr,
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mode != MCOPY_ATOMIC_NORMAL,
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page);
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}
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@ -415,7 +498,6 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
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long copied;
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struct page *page;
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bool wp_copy;
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bool zeropage = (mcopy_mode == MCOPY_ATOMIC_ZEROPAGE);
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/*
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* Sanitize the command parameters:
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@ -478,7 +560,7 @@ retry:
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if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma))
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goto out_unlock;
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if (mcopy_mode == MCOPY_ATOMIC_CONTINUE)
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if (!vma_is_shmem(dst_vma) && mcopy_mode == MCOPY_ATOMIC_CONTINUE)
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goto out_unlock;
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/*
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@ -526,7 +608,7 @@ retry:
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BUG_ON(pmd_trans_huge(*dst_pmd));
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err = mfill_atomic_pte(dst_mm, dst_pmd, dst_vma, dst_addr,
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src_addr, &page, zeropage, wp_copy);
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src_addr, &page, mcopy_mode, wp_copy);
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cond_resched();
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if (unlikely(err == -ENOENT)) {
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