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[174.91.135.175]) by smtp.gmail.com with ESMTPSA id y6sm2228726qkd.106.2021.03.22.17.50.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 22 Mar 2021 17:50:51 -0700 (PDT) From: Peter Xu To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Mike Rapoport , Nadav Amit , Jerome Glisse , Hugh Dickins , Andrea Arcangeli , Andrew Morton , "Kirill A . Shutemov" , Axel Rasmussen , peterx@redhat.com, Mike Kravetz , Matthew Wilcox Subject: [PATCH 19/23] hugetlb/userfaultfd: Handle uffd-wp special pte in hugetlb pf handler Date: Mon, 22 Mar 2021 20:50:49 -0400 Message-Id: <20210323005049.35862-1-peterx@redhat.com> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20210323004912.35132-1-peterx@redhat.com> References: <20210323004912.35132-1-peterx@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Teach the hugetlb page fault code to understand uffd-wp special pte. For example, when seeing such a pte we need to convert any write fault into a read one (which is fake - we'll retry the write later if so). Meanwhile, for handle_userfault() we'll need to make sure we must wait for the special swap pte too just like a none pte. Note that we also need to teach UFFDIO_COPY about this special pte across the code path so that we can safely install a new page at this special pte as long as we know it's a stall entry. Signed-off-by: Peter Xu --- fs/userfaultfd.c | 5 ++++- mm/hugetlb.c | 34 +++++++++++++++++++++++++++------- mm/userfaultfd.c | 5 ++++- 3 files changed, 35 insertions(+), 9 deletions(-) diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index 72956f9cc892..f6fa34f58c37 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -245,8 +245,11 @@ static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx, /* * Lockless access: we're in a wait_event so it's ok if it * changes under us. + * + * Regarding uffd-wp special case, please refer to comments in + * userfaultfd_must_wait(). */ - if (huge_pte_none(pte)) + if (huge_pte_none(pte) || pte_swp_uffd_wp_special(pte)) ret = true; if (!huge_pte_write(pte) && (reason & VM_UFFD_WP)) ret = true; diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 64e424b03774..448ef745d5ee 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4369,7 +4369,8 @@ static inline vm_fault_t hugetlb_handle_userfault(struct vm_area_struct *vma, static vm_fault_t hugetlb_no_page(struct mm_struct *mm, struct vm_area_struct *vma, struct address_space *mapping, pgoff_t idx, - unsigned long address, pte_t *ptep, unsigned int flags) + unsigned long address, pte_t *ptep, + pte_t old_pte, unsigned int flags) { struct hstate *h = hstate_vma(vma); vm_fault_t ret = VM_FAULT_SIGBUS; @@ -4493,7 +4494,7 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm, ptl = huge_pte_lock(h, mm, ptep); ret = 0; - if (!huge_pte_none(huge_ptep_get(ptep))) + if (!pte_same(huge_ptep_get(ptep), old_pte)) goto backout; if (anon_rmap) { @@ -4503,6 +4504,11 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm, page_dup_rmap(page, true); new_pte = make_huge_pte(vma, page, ((vma->vm_flags & VM_WRITE) && (vma->vm_flags & VM_SHARED))); + if (unlikely(flags & FAULT_FLAG_UFFD_WP)) { + WARN_ON_ONCE(flags & FAULT_FLAG_WRITE); + /* We should have the write bit cleared already, but be safe */ + new_pte = huge_pte_wrprotect(huge_pte_mkuffd_wp(new_pte)); + } set_huge_pte_at(mm, haddr, ptep, new_pte); hugetlb_count_add(pages_per_huge_page(h), mm); @@ -4584,9 +4590,16 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, if (unlikely(is_hugetlb_entry_migration(entry))) { migration_entry_wait_huge(vma, mm, ptep); return 0; - } else if (unlikely(is_hugetlb_entry_hwpoisoned(entry))) + } else if (unlikely(is_hugetlb_entry_hwpoisoned(entry))) { return VM_FAULT_HWPOISON_LARGE | VM_FAULT_SET_HINDEX(hstate_index(h)); + } else if (unlikely(is_swap_special_pte(entry))) { + /* Must be a uffd-wp special swap pte */ + WARN_ON_ONCE(!pte_swp_uffd_wp_special(entry)); + flags |= FAULT_FLAG_UFFD_WP; + /* Emulate a read fault */ + flags &= ~FAULT_FLAG_WRITE; + } } /* @@ -4618,8 +4631,13 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, mutex_lock(&hugetlb_fault_mutex_table[hash]); entry = huge_ptep_get(ptep); - if (huge_pte_none(entry)) { - ret = hugetlb_no_page(mm, vma, mapping, idx, address, ptep, flags); + /* + * FAULT_FLAG_UFFD_WP should be handled merely the same as pte none + * because it's basically a none pte with a special marker + */ + if (huge_pte_none(entry) || pte_swp_uffd_wp_special(entry)) { + ret = hugetlb_no_page(mm, vma, mapping, idx, address, ptep, + entry, flags); goto out_mutex; } @@ -4753,7 +4771,7 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm, unsigned long size; int vm_shared = dst_vma->vm_flags & VM_SHARED; struct hstate *h = hstate_vma(dst_vma); - pte_t _dst_pte; + pte_t _dst_pte, cur_pte; spinlock_t *ptl; int ret; struct page *page; @@ -4831,8 +4849,10 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm, if (idx >= size) goto out_release_unlock; + cur_pte = huge_ptep_get(dst_pte); ret = -EEXIST; - if (!huge_pte_none(huge_ptep_get(dst_pte))) + /* Please refer to shmem_mfill_atomic_pte() for uffd-wp special case */ + if (!huge_pte_none(cur_pte) && !pte_swp_uffd_wp_special(cur_pte)) goto out_release_unlock; if (vm_shared) { diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 01170197a3d7..a2b0dcc80a19 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -274,6 +274,8 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm, } while (src_addr < src_start + len) { + pte_t pteval; + BUG_ON(dst_addr >= dst_start + len); /* @@ -296,8 +298,9 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm, goto out_unlock; } + pteval = huge_ptep_get(dst_pte); if (mode != MCOPY_ATOMIC_CONTINUE && - !huge_pte_none(huge_ptep_get(dst_pte))) { + !huge_pte_none(pteval) && !pte_swp_uffd_wp_special(pteval)) { err = -EEXIST; mutex_unlock(&hugetlb_fault_mutex_table[hash]); i_mmap_unlock_read(mapping); -- 2.26.2