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Shutemov" , Hugh Dickins , Axel Rasmussen , Matthew Wilcox , Andrew Morton , Andrea Arcangeli , Nadav Amit Subject: [PATCH RFC 26/30] hugetlb/userfaultfd: Handle uffd-wp special pte in hugetlb pf handler Date: Fri, 15 Jan 2021 12:09:03 -0500 Message-Id: <20210115170907.24498-27-peterx@redhat.com> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20210115170907.24498-1-peterx@redhat.com> References: <20210115170907.24498-1-peterx@redhat.com> MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=peterx@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable 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: 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 s= wap 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 | 35 ++++++++++++++++++++++++++++------- mm/userfaultfd.c | 3 ++- 3 files changed, 34 insertions(+), 9 deletions(-) diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index 3190dff39d6c..3264ec46242b 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -248,8 +248,11 @@ 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 =3D true; if (!huge_pte_write(pte) && (reason & VM_UFFD_WP)) ret =3D true; diff --git a/mm/hugetlb.c b/mm/hugetlb.c index a971513cdff6..9b9f71ec30e1 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4253,7 +4253,8 @@ int huge_add_to_page_cache(struct page *page, struc= t address_space *mapping, 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 =3D hstate_vma(vma); vm_fault_t ret =3D VM_FAULT_SIGBUS; @@ -4297,6 +4298,7 @@ static vm_fault_t hugetlb_no_page(struct mm_struct = *mm, .vma =3D vma, .address =3D haddr, .flags =3D flags, + .orig_pte =3D old_pte, /* * Hard to debug if it ends up being * used by a callee that assumes @@ -4394,7 +4396,7 @@ static vm_fault_t hugetlb_no_page(struct mm_struct = *mm, =20 ptl =3D huge_pte_lock(h, mm, ptep); ret =3D 0; - if (!huge_pte_none(huge_ptep_get(ptep))) + if (!pte_same(huge_ptep_get(ptep), old_pte)) goto backout; =20 if (anon_rmap) { @@ -4404,6 +4406,11 @@ static vm_fault_t hugetlb_no_page(struct mm_struct= *mm, page_dup_rmap(page, true); new_pte =3D 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 =3D huge_pte_wrprotect(huge_pte_mkuffd_wp(new_pte)); + } set_huge_pte_at(mm, haddr, ptep, new_pte); =20 hugetlb_count_add(pages_per_huge_page(h), mm); @@ -4485,9 +4492,16 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, str= uct 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 |=3D FAULT_FLAG_UFFD_WP; + /* Emulate a read fault */ + flags &=3D ~FAULT_FLAG_WRITE; + } } =20 /* @@ -4519,8 +4533,13 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, str= uct vm_area_struct *vma, mutex_lock(&hugetlb_fault_mutex_table[hash]); =20 entry =3D huge_ptep_get(ptep); - if (huge_pte_none(entry)) { - ret =3D 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 =3D hugetlb_no_page(mm, vma, mapping, idx, address, ptep, + entry, flags); goto out_mutex; } =20 @@ -4651,7 +4670,7 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_= mm, unsigned long size; int vm_shared =3D dst_vma->vm_flags & VM_SHARED; struct hstate *h =3D hstate_vma(dst_vma); - pte_t _dst_pte; + pte_t _dst_pte, cur_pte; spinlock_t *ptl; int ret; struct page *page; @@ -4725,8 +4744,10 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst= _mm, if (idx >=3D size) goto out_release_unlock; =20 + cur_pte =3D huge_ptep_get(dst_pte); ret =3D -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; =20 if (vm_shared) { diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 3d49b888e3e8..1dff5b9a2c26 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -300,7 +300,8 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb= (struct mm_struct *dst_mm, =20 err =3D -EEXIST; dst_pteval =3D huge_ptep_get(dst_pte); - if (!huge_pte_none(dst_pteval)) { + if (!huge_pte_none(dst_pteval) && + !pte_swp_uffd_wp_special(dst_pteval)) { mutex_unlock(&hugetlb_fault_mutex_table[hash]); i_mmap_unlock_read(mapping); goto out_unlock; --=20 2.26.2