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Wed, 22 Mar 2023 07:19:05 -0700 (PDT) Received: from lucifer.home ([2a00:23c5:dc8c:8701:1663:9a35:5a7b:1d76]) by smtp.googlemail.com with ESMTPSA id f20-20020a7bcd14000000b003e203681b26sm16872855wmj.29.2023.03.22.07.19.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Mar 2023 07:19:05 -0700 (PDT) From: Lorenzo Stoakes To: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Andrew Morton Cc: Baoquan He , Uladzislau Rezki , Matthew Wilcox , David Hildenbrand , Liu Shixin , Jiri Olsa , Jens Axboe , Alexander Viro , Lorenzo Stoakes Subject: [PATCH v5 3/4] iov_iter: add copy_page_to_iter_nofault() Date: Wed, 22 Mar 2023 14:18:50 +0000 Message-Id: <50d2f757ab570dbb84e44eb84e25bd9780842d5f.1679494218.git.lstoakes@gmail.com> X-Mailer: git-send-email 2.39.2 In-Reply-To: References: MIME-Version: 1.0 X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: B1AA0100005 X-Stat-Signature: uhzij1etopc1jkrqgfxyc5mnqe5nct8w X-HE-Tag: 1679494747-690964 X-HE-Meta: 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 0EHUQGCY G/2FMufMDwh6/omekZWVOL/uKESoxH9riqh5AGGenNtr7ABeMomD9IxRcSa+jgcy83lDmsPuHeaXLVHoUyBKlZH33tmoVva5hk2uI/P/fXqDSNI40Zqjib0boNXEHwj5fXkIqK3xNX1Fs6T+ZXciOho4xob0SeOuhudUMbq8qzxLqlzQaYZh/rwM+lBSQvTIqfRbF9t0sXGZZhBqfrAJAKQbM96c7VDY/e/5hgUzEjs9dsMfzB82ihIKdHLWreprFV9wGGLNe0A0mGU4ZzGkcb8lCpm0BIPeKlmYAztuZkDwr+ugChDuM8caKKXrzMuv+qcZ8Ce6xmlpQGg/np26lHiW/cdLdlCCJ6N3ji31Y33r1TWWr0IJcKpTDwg0oDvH3opSw1mBrsB6+AD9XHXGOv5XGy0RQ+DzQ8DvCpKwTrPd61kQthInwtDf1M00XYsmBJpwZb6gsZIAqI4SBijUPwZeJa8OqjEU7mchX9p3rH7VKVfQ= 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: Provide a means to copy a page to user space from an iterator, aborting if a page fault would occur. This supports compound pages, but may be passed a tail page with an offset extending further into the compound page, so we cannot pass a folio. This allows for this function to be called from atomic context and _try_ to user pages if they are faulted in, aborting if not. The function does not use _copy_to_iter() in order to not specify might_fault(), this is similar to copy_page_from_iter_atomic(). This is being added in order that an iteratable form of vread() can be implemented while holding spinlocks. Signed-off-by: Lorenzo Stoakes --- include/linux/uio.h | 2 ++ lib/iov_iter.c | 36 ++++++++++++++++++++++++++++++++++++ 2 files changed, 38 insertions(+) diff --git a/include/linux/uio.h b/include/linux/uio.h index 27e3fd942960..29eb18bb6feb 100644 --- a/include/linux/uio.h +++ b/include/linux/uio.h @@ -173,6 +173,8 @@ static inline size_t copy_folio_to_iter(struct folio *folio, size_t offset, { return copy_page_to_iter(&folio->page, offset, bytes, i); } +size_t copy_page_to_iter_nofault(struct page *page, unsigned offset, + size_t bytes, struct iov_iter *i); static __always_inline __must_check size_t copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i) diff --git a/lib/iov_iter.c b/lib/iov_iter.c index 274014e4eafe..b286cfea4bee 100644 --- a/lib/iov_iter.c +++ b/lib/iov_iter.c @@ -734,6 +734,42 @@ size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes, } EXPORT_SYMBOL(copy_page_to_iter); +size_t copy_page_to_iter_nofault(struct page *page, unsigned offset, size_t bytes, + struct iov_iter *i) +{ + size_t res = 0; + + if (!page_copy_sane(page, offset, bytes)) + return 0; + if (WARN_ON_ONCE(i->data_source)) + return 0; + if (unlikely(iov_iter_is_pipe(i))) + return copy_page_to_iter_pipe(page, offset, bytes, i); + page += offset / PAGE_SIZE; // first subpage + offset %= PAGE_SIZE; + while (1) { + void *kaddr = kmap_local_page(page); + size_t n = min(bytes, (size_t)PAGE_SIZE - offset); + + iterate_and_advance(i, n, base, len, off, + copy_to_user_nofault(base, kaddr + offset + off, len), + memcpy(base, kaddr + offset + off, len) + ) + kunmap_local(kaddr); + res += n; + bytes -= n; + if (!bytes || !n) + break; + offset += n; + if (offset == PAGE_SIZE) { + page++; + offset = 0; + } + } + return res; +} +EXPORT_SYMBOL(copy_page_to_iter_nofault); + size_t copy_page_from_iter(struct page *page, size_t offset, size_t bytes, struct iov_iter *i) {