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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1qgqoH-004PI8-7U; Thu, 14 Sep 2023 18:11:25 +0000 Date: Thu, 14 Sep 2023 19:11:25 +0100 From: Matthew Wilcox To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, viro@zeniv.linux.org.uk, brauner@kernel.org, shuah@kernel.org, aarcange@redhat.com, lokeshgidra@google.com, peterx@redhat.com, david@redhat.com, hughd@google.com, mhocko@suse.com, axelrasmussen@google.com, rppt@kernel.org, Liam.Howlett@oracle.com, jannh@google.com, zhangpeng362@huawei.com, bgeffon@google.com, kaleshsingh@google.com, ngeoffray@google.com, jdduke@google.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH 2/3] userfaultfd: UFFDIO_REMAP uABI Message-ID: References: <20230914152620.2743033-1-surenb@google.com> <20230914152620.2743033-3-surenb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230914152620.2743033-3-surenb@google.com> X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: BDE1318000D X-Stat-Signature: cxufhfmazgk14wg3j3fsiqyb51t8wgwx X-HE-Tag: 1694715100-26068 X-HE-Meta: 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 QMCarDgZ aFaRvWIY3dKKq5v7hZ7CtIBqngu9GpRm2rjMiQIBOe6PK2PKsZi8WHiInJPYnLBOwfQlfDolNqrh6tQYlfq3KJf12zCvTU3kiRFrQxEME757gAF4mnMxbftNkCIDlQCXUvxg2My/KwXXmRnhTt15tgknGIHPleou2J/5hrt6hFQSKR2EGBKFF1K3D6w== 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: On Thu, Sep 14, 2023 at 08:26:12AM -0700, Suren Baghdasaryan wrote: > +++ b/include/linux/userfaultfd_k.h > @@ -93,6 +93,23 @@ extern int mwriteprotect_range(struct mm_struct *dst_mm, > extern long uffd_wp_range(struct vm_area_struct *vma, > unsigned long start, unsigned long len, bool enable_wp); > > +/* remap_pages */ > +extern void double_pt_lock(spinlock_t *ptl1, spinlock_t *ptl2); > +extern void double_pt_unlock(spinlock_t *ptl1, spinlock_t *ptl2); > +extern ssize_t remap_pages(struct mm_struct *dst_mm, > + struct mm_struct *src_mm, > + unsigned long dst_start, > + unsigned long src_start, > + unsigned long len, __u64 flags); > +extern int remap_pages_huge_pmd(struct mm_struct *dst_mm, > + struct mm_struct *src_mm, > + pmd_t *dst_pmd, pmd_t *src_pmd, > + pmd_t dst_pmdval, > + struct vm_area_struct *dst_vma, > + struct vm_area_struct *src_vma, > + unsigned long dst_addr, > + unsigned long src_addr); Drop the 'extern' markers from function declarations. > +int remap_pages_huge_pmd(struct mm_struct *dst_mm, > + struct mm_struct *src_mm, > + pmd_t *dst_pmd, pmd_t *src_pmd, > + pmd_t dst_pmdval, > + struct vm_area_struct *dst_vma, > + struct vm_area_struct *src_vma, > + unsigned long dst_addr, > + unsigned long src_addr) > +{ > + pmd_t _dst_pmd, src_pmdval; > + struct page *src_page; > + struct anon_vma *src_anon_vma, *dst_anon_vma; > + spinlock_t *src_ptl, *dst_ptl; > + pgtable_t pgtable; > + struct mmu_notifier_range range; > + > + src_pmdval = *src_pmd; > + src_ptl = pmd_lockptr(src_mm, src_pmd); > + > + BUG_ON(!pmd_trans_huge(src_pmdval)); > + BUG_ON(!pmd_none(dst_pmdval)); > + BUG_ON(!spin_is_locked(src_ptl)); > + mmap_assert_locked(src_mm); > + mmap_assert_locked(dst_mm); > + BUG_ON(src_addr & ~HPAGE_PMD_MASK); > + BUG_ON(dst_addr & ~HPAGE_PMD_MASK); > + > + src_page = pmd_page(src_pmdval); > + BUG_ON(!PageHead(src_page)); > + BUG_ON(!PageAnon(src_page)); Better to add a src_folio = page_folio(src_page); and then folio_test_anon() here. > + if (unlikely(page_mapcount(src_page) != 1)) { Brr, this is going to miss PTE mappings of this folio. I think you actually want folio_mapcount() instead, although it'd be more efficient to look at folio->_entire_mapcount == 1 and _nr_pages_mapped == 0. Not wure what a good name for that predicate would be. > + get_page(src_page); folio_get() > + /* block all concurrent rmap walks */ > + lock_page(src_page); folio_lock() > + /* > + * split_huge_page walks the anon_vma chain without the page > + * lock. Serialize against it with the anon_vma lock, the page > + * lock is not enough. > + */ > + src_anon_vma = folio_get_anon_vma(page_folio(src_page)); ... > + if (!src_anon_vma) { > + unlock_page(src_page); folio_unlock() > + put_page(src_page); folio_put() > + if (unlikely(!pmd_same(*src_pmd, src_pmdval) || > + !pmd_same(*dst_pmd, dst_pmdval) || > + page_mapcount(src_page) != 1)) { similar folio_total_mapcount() > + double_pt_unlock(src_ptl, dst_ptl); > + anon_vma_unlock_write(src_anon_vma); > + put_anon_vma(src_anon_vma); > + unlock_page(src_page); > + put_page(src_page); ... > + BUG_ON(!PageHead(src_page)); > + BUG_ON(!PageAnon(src_page)); > + /* the PT lock is enough to keep the page pinned now */ > + put_page(src_page); ... > + dst_anon_vma = (void *) dst_vma->anon_vma + PAGE_MAPPING_ANON; > + WRITE_ONCE(src_page->mapping, (struct address_space *) dst_anon_vma); > + WRITE_ONCE(src_page->index, linear_page_index(dst_vma, dst_addr)); Definitely want to use the folio here. > + /* unblock rmap walks */ > + unlock_page(src_page); ... > +static int remap_pages_pte(struct mm_struct *dst_mm, > + struct mm_struct *src_mm, > + pmd_t *dst_pmd, > + pmd_t *src_pmd, > + struct vm_area_struct *dst_vma, > + struct vm_area_struct *src_vma, > + unsigned long dst_addr, > + unsigned long src_addr, > + __u64 mode) > +{ > + swp_entry_t entry; > + pte_t orig_src_pte, orig_dst_pte; > + spinlock_t *src_ptl, *dst_ptl; > + pte_t *src_pte = NULL; > + pte_t *dst_pte = NULL; > + > + struct folio *src_folio = NULL; > + struct anon_vma *src_anon_vma = NULL; > + struct anon_vma *dst_anon_vma; > + struct mmu_notifier_range range; > + int err = 0; > + > +retry: > + dst_pte = pte_offset_map_nolock(dst_mm, dst_pmd, dst_addr, &dst_ptl); > + > + /* If an huge pmd materialized from under us fail */ > + if (unlikely(!dst_pte)) { > + err = -EFAULT; > + goto out; > + } > + > + src_pte = pte_offset_map_nolock(src_mm, src_pmd, src_addr, &src_ptl); > + > + /* > + * We held the mmap_lock for reading so MADV_DONTNEED > + * can zap transparent huge pages under us, or the > + * transparent huge page fault can establish new > + * transparent huge pages under us. > + */ > + if (unlikely(!src_pte)) { > + err = -EFAULT; > + goto out; > + } > + > + BUG_ON(pmd_none(*dst_pmd)); > + BUG_ON(pmd_none(*src_pmd)); > + BUG_ON(pmd_trans_huge(*dst_pmd)); > + BUG_ON(pmd_trans_huge(*src_pmd)); > + > + spin_lock(dst_ptl); > + orig_dst_pte = *dst_pte; > + spin_unlock(dst_ptl); > + if (!pte_none(orig_dst_pte)) { > + err = -EEXIST; > + goto out; > + } > + > + spin_lock(src_ptl); > + orig_src_pte = *src_pte; > + spin_unlock(src_ptl); > + if (pte_none(orig_src_pte)) { > + if (!(mode & UFFDIO_REMAP_MODE_ALLOW_SRC_HOLES)) > + err = -ENOENT; > + else /* nothing to do to remap a hole */ > + err = 0; > + goto out; > + } > + > + if (pte_present(orig_src_pte)) { > + if (!src_folio) { > + struct folio *folio; > + > + /* > + * Pin the page while holding the lock to be sure the > + * page isn't freed under us > + */ > + spin_lock(src_ptl); > + if (!pte_same(orig_src_pte, *src_pte)) { > + spin_unlock(src_ptl); > + err = -EAGAIN; > + goto out; > + } > + > + folio = vm_normal_folio(src_vma, src_addr, orig_src_pte); > + if (!folio || !folio_test_anon(folio) || > + folio_estimated_sharers(folio) != 1) { I wonder if we also want to fail if folio_test_large()? While we don't have large anon folios today, it seems to me that trying to migrate one of them like this is just not going to work.