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[174.93.75.154]) by smtp.gmail.com with ESMTPSA id c14sm457297qtc.5.2021.04.20.18.02.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 Apr 2021 18:02:07 -0700 (PDT) Date: Tue, 20 Apr 2021 21:02:05 -0400 From: Peter Xu To: Axel Rasmussen Cc: Alexander Viro , Andrea Arcangeli , Andrew Morton , Hugh Dickins , Jerome Glisse , Joe Perches , Lokesh Gidra , Mike Kravetz , Mike Rapoport , Shaohua Li , Shuah Khan , Stephen Rothwell , Wang Qing , linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, Brian Geffon , "Dr . David Alan Gilbert" , Mina Almasry , Oliver Upton Subject: Re: [PATCH v4 09/10] userfaultfd/shmem: modify shmem_mcopy_atomic_pte to use install_pte() Message-ID: <20210421010205.GH4440@xz-x1> References: <20210420220804.486803-1-axelrasmussen@google.com> <20210420220804.486803-10-axelrasmussen@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20210420220804.486803-10-axelrasmussen@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org On Tue, Apr 20, 2021 at 03:08:03PM -0700, Axel Rasmussen wrote: > In a previous commit, we added the mcopy_atomic_install_pte() helper. > This helper does the job of setting up PTEs for an existing page, to map > it into a given VMA. It deals with both the anon and shmem cases, as > well as the shared and private cases. > > In other words, shmem_mcopy_atomic_pte() duplicates a case it already > handles. So, expose it, and let shmem_mcopy_atomic_pte() use it > directly, to reduce code duplication. > > This requires that we refactor shmem_mcopy_atomic_pte() a bit: > > Instead of doing accounting (shmem_recalc_inode() et al) part-way > through the PTE setup, do it beforehand. This frees up > mcopy_atomic_install_pte() from having to care about this accounting, > but it does mean we need to clean it up if we get a failure afterwards > (shmem_uncharge()). > > We can *almost* use shmem_charge() to do this, reducing code > duplication. But, it does `inode->i_mapping->nrpages++`, which would > double-count since shmem_add_to_page_cache() also does this. Missing to mention the lru_cache_add() replacement comment as Hugh commented on this? > > Signed-off-by: Axel Rasmussen > --- > include/linux/userfaultfd_k.h | 5 ++++ > mm/shmem.c | 53 ++++++++--------------------------- > mm/userfaultfd.c | 17 ++++------- > 3 files changed, 22 insertions(+), 53 deletions(-) > > diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h > index 794d1538b8ba..39c094cc6641 100644 > --- a/include/linux/userfaultfd_k.h > +++ b/include/linux/userfaultfd_k.h > @@ -53,6 +53,11 @@ enum mcopy_atomic_mode { > MCOPY_ATOMIC_CONTINUE, > }; > > +extern int mcopy_atomic_install_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd, > + struct vm_area_struct *dst_vma, > + unsigned long dst_addr, struct page *page, > + bool newly_allocated, bool wp_copy); > + > extern ssize_t mcopy_atomic(struct mm_struct *dst_mm, unsigned long dst_start, > unsigned long src_start, unsigned long len, > bool *mmap_changing, __u64 mode); > diff --git a/mm/shmem.c b/mm/shmem.c > index 30c0bb501dc9..9bfa80fcd414 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -2378,10 +2378,8 @@ int shmem_mcopy_atomic_pte(struct mm_struct *dst_mm, > struct address_space *mapping = inode->i_mapping; > gfp_t gfp = mapping_gfp_mask(mapping); > pgoff_t pgoff = linear_page_index(dst_vma, dst_addr); > - spinlock_t *ptl; > void *page_kaddr; > struct page *page; > - pte_t _dst_pte, *dst_pte; > int ret; > pgoff_t max_off; > > @@ -2391,8 +2389,10 @@ int shmem_mcopy_atomic_pte(struct mm_struct *dst_mm, > > if (!*pagep) { > page = shmem_alloc_page(gfp, info, pgoff); > - if (!page) > - goto out_unacct_blocks; > + if (!page) { > + shmem_inode_unacct_blocks(inode, 1); > + goto out; > + } > > if (!zeropage) { /* COPY */ > page_kaddr = kmap_atomic(page); > @@ -2432,59 +2432,28 @@ int shmem_mcopy_atomic_pte(struct mm_struct *dst_mm, > if (ret) > 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 { > - /* > - * We don't set the pte dirty if the vma has no > - * VM_WRITE permission, so mark the page dirty or it > - * could be freed from under us. We could do it > - * unconditionally before unlock_page(), but doing it > - * only if VM_WRITE is not set is faster. > - */ > - set_page_dirty(page); > - } > - > - dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl); > - > - ret = -EFAULT; > - max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE); > - if (unlikely(pgoff >= max_off)) > - goto out_release_unlock; > - > - ret = -EEXIST; > - if (!pte_none(*dst_pte)) > - goto out_release_unlock; > - > - lru_cache_add(page); > - > spin_lock_irq(&info->lock); > info->alloced++; > inode->i_blocks += BLOCKS_PER_PAGE; > shmem_recalc_inode(inode); > spin_unlock_irq(&info->lock); > > - inc_mm_counter(dst_mm, mm_counter_file(page)); > - page_add_file_rmap(page, false); > - set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte); > + ret = mcopy_atomic_install_pte(dst_mm, dst_pmd, dst_vma, dst_addr, > + page, true, false); > + if (ret) > + goto out_release_uncharge; > > - /* No need to invalidate - it was non-present before */ > - update_mmu_cache(dst_vma, dst_addr, dst_pte); > - pte_unmap_unlock(dst_pte, ptl); > + SetPageDirty(page); > unlock_page(page); > ret = 0; > out: > return ret; > -out_release_unlock: > - pte_unmap_unlock(dst_pte, ptl); > - ClearPageDirty(page); > +out_release_uncharge: > delete_from_page_cache(page); > + shmem_uncharge(inode, 1); > out_release: > unlock_page(page); > put_page(page); > -out_unacct_blocks: Will all the "goto out_release" miss one call to shmem_inode_unacct_blocks()? > - shmem_inode_unacct_blocks(inode, 1); > goto out; > } > #endif /* CONFIG_USERFAULTFD */ > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > index 51d8c0127161..3a9ddbb2dbbd 100644 > --- a/mm/userfaultfd.c > +++ b/mm/userfaultfd.c > @@ -51,18 +51,13 @@ struct vm_area_struct *find_dst_vma(struct mm_struct *dst_mm, > /* > * Install PTEs, to map dst_addr (within dst_vma) to page. > * > - * This function handles MCOPY_ATOMIC_CONTINUE (which is always file-backed), > - * whether or not dst_vma is VM_SHARED. It also handles the more general > - * MCOPY_ATOMIC_NORMAL case, when dst_vma is *not* VM_SHARED (it may be file > - * backed, or not). > - * > - * Note that MCOPY_ATOMIC_NORMAL for a VM_SHARED dst_vma is handled by > - * shmem_mcopy_atomic_pte instead. > + * This function handles both MCOPY_ATOMIC_NORMAL and _CONTINUE for both shmem > + * and anon, and for both shared and private VMAs. > */ > -static int mcopy_atomic_install_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd, > - struct vm_area_struct *dst_vma, > - unsigned long dst_addr, struct page *page, > - bool newly_allocated, bool wp_copy) > +int mcopy_atomic_install_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd, > + struct vm_area_struct *dst_vma, > + unsigned long dst_addr, struct page *page, > + bool newly_allocated, bool wp_copy) > { > int ret; > pte_t _dst_pte, *dst_pte; > -- > 2.31.1.368.gbe11c130af-goog > -- Peter Xu