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Wong" Date: Tue, 3 Aug 2021 21:18:11 +0200 Message-Id: <20210803191818.993968-6-agruenba@redhat.com> In-Reply-To: <20210803191818.993968-1-agruenba@redhat.com> References: <20210803191818.993968-1-agruenba@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Proofpoint-SPF-Result: pass X-Proofpoint-SPF-Record: v=spf1 ip4:103.23.64.2 ip4:103.23.65.2 ip4:103.23.66.26 ip4:103.23.67.26 ip4:107.21.15.141 ip4:108.177.8.0/21 ip4:128.17.0.0/20 ip4:128.17.128.0/20 ip4:128.17.192.0/20 ip4:128.17.64.0/20 ip4:128.245.0.0/20 ip4:128.245.64.0/20 ip4:13.110.208.0/21 ip4:13.111.0.0/16 ip4:136.147.128.0/20 ip4:136.147.176.0/20 ip4:148.105.8.0/21 ip4:148.139.0.2 include:spf1.redhat.com -all X-Proofpoint-SPF-VenPass: Allowed X-Source-IP: 216.205.24.124 X-ServerName: us-smtp-delivery-124.mimecast.com X-Proofpoint-SPF-Result: pass X-Proofpoint-SPF-Record: v=spf1 ip4:103.23.64.2 ip4:103.23.65.2 ip4:103.23.66.26 ip4:103.23.67.26 ip4:107.21.15.141 ip4:108.177.8.0/21 ip4:128.17.0.0/20 ip4:128.17.128.0/20 ip4:128.17.192.0/20 ip4:128.17.64.0/20 ip4:128.245.0.0/20 ip4:128.245.64.0/20 ip4:13.110.208.0/21 ip4:13.111.0.0/16 ip4:136.147.128.0/20 ip4:136.147.176.0/20 ip4:148.105.8.0/21 ip4:148.139.0.2 include:spf1.redhat.com -all X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=10065 signatures=668682 X-Proofpoint-Spam-Reason: safe X-Spam: OrgSafeList X-SpamRule: orgsafelist X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=10065 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxscore=0 malwarescore=0 phishscore=0 spamscore=0 adultscore=0 suspectscore=0 mlxlogscore=999 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2107140000 definitions=main-2108030123 Cc: Jan Kara , Andreas Gruenbacher , linux-kernel@vger.kernel.org, cluster-devel@redhat.com, linux-fsdevel@vger.kernel.org, ocfs2-devel@oss.oracle.com Subject: [Ocfs2-devel] [PATCH v5 05/12] iov_iter: Introduce fault_in_iov_iter_writeable X-BeenThere: ocfs2-devel@oss.oracle.com X-Mailman-Version: 2.1.9 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: ocfs2-devel-bounces@oss.oracle.com Errors-To: ocfs2-devel-bounces@oss.oracle.com X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=10065 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxscore=0 malwarescore=0 phishscore=0 spamscore=0 adultscore=0 suspectscore=0 mlxlogscore=999 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2107140000 definitions=main-2108030123 X-Proofpoint-ORIG-GUID: IRQToAGmuYaawL9pRNlXPIzmuAx4RO92 X-Proofpoint-GUID: IRQToAGmuYaawL9pRNlXPIzmuAx4RO92 Introduce a new fault_in_iov_iter_writeable helper for safely faulting in an iterator for writing. Uses get_user_pages() to fault in the pages without actually writing to them, which would be destructive. We'll use fault_in_iov_iter_writeable in gfs2 once we've determined that the iterator passed to .read_iter isn't in memory. Signed-off-by: Andreas Gruenbacher --- include/linux/pagemap.h | 1 + include/linux/uio.h | 1 + lib/iov_iter.c | 41 +++++++++++++++++++++++++++ mm/gup.c | 61 +++++++++++++++++++++++++++++++++++++++++ 4 files changed, 104 insertions(+) diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index 7c9edc9694d9..a629807edb8c 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -737,6 +737,7 @@ extern void add_page_wait_queue(struct page *page, wait_queue_entry_t *waiter); * Fault in userspace address range. */ size_t fault_in_writeable(char __user *uaddr, size_t size); +size_t fault_in_safe_writeable(const char __user *uaddr, size_t size); size_t fault_in_readable(const char __user *uaddr, size_t size); int add_to_page_cache_locked(struct page *page, struct address_space *mapping, diff --git a/include/linux/uio.h b/include/linux/uio.h index 12d30246c2e9..ffa431aeb067 100644 --- a/include/linux/uio.h +++ b/include/linux/uio.h @@ -120,6 +120,7 @@ size_t copy_page_from_iter_atomic(struct page *page, unsigned offset, void iov_iter_advance(struct iov_iter *i, size_t bytes); void iov_iter_revert(struct iov_iter *i, size_t bytes); size_t fault_in_iov_iter_readable(const struct iov_iter *i, size_t bytes); +size_t fault_in_iov_iter_writeable(const struct iov_iter *i, size_t bytes); size_t iov_iter_single_seg_count(const struct iov_iter *i); size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes, struct iov_iter *i); diff --git a/lib/iov_iter.c b/lib/iov_iter.c index c0fa1618561c..4ffc76801eaa 100644 --- a/lib/iov_iter.c +++ b/lib/iov_iter.c @@ -471,6 +471,47 @@ size_t fault_in_iov_iter_readable(const struct iov_iter *i, size_t size) } EXPORT_SYMBOL(fault_in_iov_iter_readable); +/* + * fault_in_iov_iter_writeable - fault in iov iterator for writing + * @i: iterator + * @size: maximum length + * + * Faults in the iterator using get_user_pages(), i.e., without triggering + * hardware page faults. This is primarily useful when we know that some or + * all of the pages in @i aren't in memory. + * + * Returns the number of bytes faulted in, or 0 if no bytes could be faulted in + * (i.e., because the address is invalid). + * + * Always returns the number of avaliable bytes for non-user space iterators. + */ +size_t fault_in_iov_iter_writeable(const struct iov_iter *i, size_t size) +{ + if (size > i->count) + size = i->count; + + if (iter_is_iovec(i)) { + const struct iovec *p; + size_t bytes = size; + size_t skip; + + for (p = i->iov, skip = i->iov_offset; bytes; p++, skip = 0) { + size_t len = min(bytes, p->iov_len - skip); + size_t ret; + + if (unlikely(!len)) + continue; + ret = fault_in_safe_writeable(p->iov_base + skip, len); + bytes -= ret; + if (ret != len) + break; + } + return size - bytes; + } + return size; +} +EXPORT_SYMBOL(fault_in_iov_iter_writeable); + void iov_iter_init(struct iov_iter *i, unsigned int direction, const struct iovec *iov, unsigned long nr_segs, size_t count) diff --git a/mm/gup.c b/mm/gup.c index d04984d5d93c..7218e27c2481 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -1694,6 +1694,67 @@ size_t fault_in_writeable(char __user *uaddr, size_t size) } EXPORT_SYMBOL(fault_in_writeable); +/** + * fault_in_safe_writeable - fault in an address range for writing + * @uaddr: start of address range + * @size: length of address range + * + * Faults in an address range using get_user_pages, i.e., without triggering + * hardware page faults. This is primarily useful when we know that some or + * all of the pages in the address range aren't in memory. + * + * Other than fault_in_writeable(), this function is non-destructive. + * + * Note that we don't pin or otherwise hold the pages referenced that we fault + * in. There's no guarantee that they'll stay in memory for any duration of + * time. + * + * Returns the number of bytes faulted in from @uaddr. + */ +size_t fault_in_safe_writeable(const char __user *uaddr, size_t size) +{ + unsigned long start = (unsigned long)uaddr; + unsigned long end, nstart, nend; + struct mm_struct *mm = current->mm; + struct vm_area_struct *vma = NULL; + int locked = 0; + + /* FIXME: Protect against overflow! */ + + end = PAGE_ALIGN(start + size); + for (nstart = start & PAGE_MASK; nstart < end; nstart = nend) { + unsigned long nr_pages; + long ret; + + if (!locked) { + locked = 1; + mmap_read_lock(mm); + vma = find_vma(mm, nstart); + } else if (nstart >= vma->vm_end) + vma = vma->vm_next; + if (!vma || vma->vm_start >= end) + break; + nend = min(end, vma->vm_end); + if (vma->vm_flags & (VM_IO | VM_PFNMAP)) + continue; + if (nstart < vma->vm_start) + nstart = vma->vm_start; + nr_pages = (nend - nstart) / PAGE_SIZE; + ret = __get_user_pages_locked(mm, nstart, nr_pages, + NULL, NULL, &locked, + FOLL_TOUCH | FOLL_WRITE); + if (ret <= 0) + break; + nend = nstart + ret * PAGE_SIZE; + } + if (locked) + mmap_read_unlock(mm); + if (nstart > start) + return min(nstart - start, size); + return 0; +} +EXPORT_SYMBOL(fault_in_safe_writeable); + size_t fault_in_readable(const char __user *uaddr, size_t size) { const char __user *start = uaddr, *end;