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[2003:cb:c71c:600:4630:4a91:d07:7095]) by smtp.gmail.com with ESMTPSA id q5-20020a5d6585000000b0031accc7228asm2463536wru.34.2023.09.14.11.43.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 14 Sep 2023 11:43:38 -0700 (PDT) Message-ID: Date: Thu, 14 Sep 2023 20:43:36 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH 2/3] userfaultfd: UFFDIO_REMAP uABI To: Matthew Wilcox , 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, 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 References: <20230914152620.2743033-1-surenb@google.com> <20230914152620.2743033-3-surenb@google.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: g1nik8xcmfg5u69genb831qihjzrj35b X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 1E8CC180021 X-HE-Tag: 1694717022-766942 X-HE-Meta: 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 sg9xXKWh U2Zz/cUJhiUFQJIJg61Rg6TdMZCqTIsqOjflhHFRVzfeptTSSyDpe43uVoqdRS/iej+10vkt9UmD7P2MZlD8pqb4as1Fcsk3vn2mc0HD6jrLhool8ouU+niGj1TKAMI6t9ggnMv8b5Qa3LfhtPlfaMQ9HDb4LcUMwmOvKYTPfOrcV1CIceHRtyBtT5nyb9IGNHw+F0zwn88bSTHBvk/otlubOAqfNEXEwFHnbfHoXo6yXq1AcxDnRVqDPORk1tdgQA76mQWAhfBPn/QIpEjq6HdueDpZVZor9w5qVXkMgsAo4ahroEYF72ogBAvXLXcCX5ZBDLzkfUgUPrYbKnKD2WsrswIDAkfHXjydoZ3t39Ua9FvrzcxcdHVntul52B6WTyOBkEqrQ/+dQADn0kiRJq8Y8PDEN83xrQ75JaCQXP3rffek= 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 14.09.23 20:11, Matthew Wilcox wrote: > 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. We have * It only works on non shared anonymous pages because those can * be relocated without generating non linear anon_vmas in the rmap * code. * * It provides a zero copy mechanism to handle userspace page faults. * The source vma pages should have mapcount == 1, which can be * enforced by using madvise(MADV_DONTFORK) on src vma. Use PageAnonExclusive(). As long as KSM is not involved and you don't use fork(), that flag should be good enough for that use case here. [...] >> + /* >> + * 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. Yes, refuse any PTE-mapped large folios. -- Cheers, David / dhildenb