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[184.144.111.238]) by smtp.gmail.com with ESMTPSA id 5sm3090802qkr.100.2021.07.15.13.16.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 15 Jul 2021 13:16:42 -0700 (PDT) From: Peter Xu To: linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: Axel Rasmussen , Nadav Amit , Jerome Glisse , "Kirill A . Shutemov" , Jason Gunthorpe , Alistair Popple , Andrew Morton , David Hildenbrand , peterx@redhat.com, Andrea Arcangeli , Matthew Wilcox , Mike Kravetz , Tiberiu Georgescu , Hugh Dickins , Miaohe Lin , Mike Rapoport Subject: [PATCH v5 21/26] hugetlb/userfaultfd: Handle uffd-wp special pte in hugetlb pf handler Date: Thu, 15 Jul 2021 16:16:39 -0400 Message-Id: <20210715201639.211982-1-peterx@redhat.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210715201422.211004-1-peterx@redhat.com> References: <20210715201422.211004-1-peterx@redhat.com> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="US-ASCII" Authentication-Results: imf06.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=NJ4kh69N; spf=none (imf06.hostedemail.com: domain of peterx@redhat.com has no SPF policy when checking 216.205.24.124) smtp.mailfrom=peterx@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Stat-Signature: z8e15gdn7weagnz3caoqsr1jbp8kwjc9 X-Rspamd-Queue-Id: 0B26D801CFB5 X-Rspamd-Server: rspam01 X-HE-Tag: 1626380204-898033 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 | 26 ++++++++++++++++++++------ mm/userfaultfd.c | 5 ++++- 3 files changed, 28 insertions(+), 8 deletions(-) diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index e1c1cbc7bcc8..644df737fbb2 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 =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 517ee30f272c..5941b5cd7ecc 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4786,7 +4786,8 @@ static inline vm_fault_t hugetlb_handle_userfault(s= truct 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 =3D hstate_vma(vma); vm_fault_t ret =3D VM_FAULT_SIGBUS; @@ -4910,7 +4911,7 @@ 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) { @@ -4920,6 +4921,12 @@ 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 this pte was previously wr-protected, keep it wr-protected even + * if populated. + */ + if (unlikely(pte_swp_uffd_wp_special(old_pte))) + 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); @@ -5035,8 +5042,13 @@ 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); + /* + * uffd-wp-special 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 @@ -5170,7 +5182,7 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_= mm, pgoff_t idx =3D vma_hugecache_offset(h, dst_vma, dst_addr); unsigned long size; int vm_shared =3D dst_vma->vm_flags & VM_SHARED; - pte_t _dst_pte; + pte_t _dst_pte, cur_pte; spinlock_t *ptl; int ret =3D -ENOMEM; struct page *page; @@ -5287,8 +5299,10 @@ 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 7ba721aca1c5..a8038903effd 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -363,6 +363,8 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb= (struct mm_struct *dst_mm, } =20 while (src_addr < src_start + len) { + pte_t pteval; + BUG_ON(dst_addr >=3D dst_start + len); =20 /* @@ -385,8 +387,9 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb= (struct mm_struct *dst_mm, goto out_unlock; } =20 + pteval =3D huge_ptep_get(dst_pte); if (mode !=3D MCOPY_ATOMIC_CONTINUE && - !huge_pte_none(huge_ptep_get(dst_pte))) { + !huge_pte_none(pteval) && !pte_swp_uffd_wp_special(pteval)) { err =3D -EEXIST; mutex_unlock(&hugetlb_fault_mutex_table[hash]); i_mmap_unlock_read(mapping); --=20 2.31.1