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Registered in England and Wales under Company Registration No. 3798903 Subject: [RFC PATCH 01/12] mm: Move FOLL_* defs to mm_types.h From: David Howells To: Steve French , Al Viro Cc: Matthew Wilcox , John Hubbard , linux-mm@vger.kernel.org, linux-fsdevel@vger.kernel.org, dhowells@redhat.com, Shyam Prasad N , Rohith Surabattula , Tom Talpey , Christoph Hellwig , Matthew Wilcox , Jeff Layton , linux-cifs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Date: Tue, 01 Nov 2022 16:30:50 +0000 Message-ID: <166732025009.3186319.3402781784409891214.stgit@warthog.procyon.org.uk> In-Reply-To: <166732024173.3186319.18204305072070871546.stgit@warthog.procyon.org.uk> References: <166732024173.3186319.18204305072070871546.stgit@warthog.procyon.org.uk> User-Agent: StGit/1.5 MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.4 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com ARC-Authentication-Results: i=1; imf11.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=dFD1NB1l; spf=pass (imf11.hostedemail.com: domain of dhowells@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=dhowells@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1667322007; a=rsa-sha256; cv=none; b=w84kvwzCuxIZDJhuXjP4bNZnK4T+4c2Flfz0WwO5D2SaHMo+akoUgvvYHnmNduYX+LgsIw EM2nlF76IHu6j+Dj9YGIOhHrauO4z2kA2MqRtULUu+iGe1Oq4e86a0zhc1cSTI/RCOFUSK RrWnp2K29Ny9mHzCFBMmHAU51UdtaUQ= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1667322007; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding:resent-to: resent-from:resent-message-id:in-reply-to:in-reply-to: references:references:dkim-signature; bh=/J12QSKNwXmqc00XDkAeYq6EXRWO58wkRfpy1g5AG8Q=; b=w9ZLIcM81lPHfV3555gSG5m47di1aWmDykUvtBSgGRkLlKBZ++Qh/2ElaLpKmo5HD6fo8F EknE1IJuus+OKqgQEBufRF87xdJFj39/i46191IjMKiYD/VWYVBrNLUnBs00GNAztIXz9o 29yHffAIzew074dFWOX/otR26ZPLfgY= X-Stat-Signature: yio6sp7yqzs6d8cs8mkm4k71nnj9aypi X-Rspamd-Queue-Id: 5ADD940049 Authentication-Results: imf11.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=dFD1NB1l; spf=pass (imf11.hostedemail.com: domain of dhowells@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=dhowells@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspamd-Server: rspam03 X-Rspam-User: X-HE-Tag: 1667322007-177143 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: Move FOLL_* definitions to linux/mm_types.h to make them more accessible without having to drag in all of linux/mm.h and everything that drags in too[1]. Suggested-by: Matthew Wilcox Signed-off-by: David Howells cc: John Hubbard cc: Al Viro cc: linux-mm@vger.kernel.org cc: linux-fsdevel@vger.kernel.org Link: https://lore.kernel.org/linux-fsdevel/Y1%2FhSO+7kAJhGShG@casper.infradead.org/ [1] --- include/linux/mm.h | 74 ---------------------------------------------- include/linux/mm_types.h | 73 +++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 73 insertions(+), 74 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 8bbcccbc5565..7a7a287818ad 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -2941,80 +2941,6 @@ static inline vm_fault_t vmf_error(int err) struct page *follow_page(struct vm_area_struct *vma, unsigned long address, unsigned int foll_flags); -#define FOLL_WRITE 0x01 /* check pte is writable */ -#define FOLL_TOUCH 0x02 /* mark page accessed */ -#define FOLL_GET 0x04 /* do get_page on page */ -#define FOLL_DUMP 0x08 /* give error on hole if it would be zero */ -#define FOLL_FORCE 0x10 /* get_user_pages read/write w/o permission */ -#define FOLL_NOWAIT 0x20 /* if a disk transfer is needed, start the IO - * and return without waiting upon it */ -#define FOLL_NOFAULT 0x80 /* do not fault in pages */ -#define FOLL_HWPOISON 0x100 /* check page is hwpoisoned */ -#define FOLL_MIGRATION 0x400 /* wait for page to replace migration entry */ -#define FOLL_TRIED 0x800 /* a retry, previous pass started an IO */ -#define FOLL_REMOTE 0x2000 /* we are working on non-current tsk/mm */ -#define FOLL_ANON 0x8000 /* don't do file mappings */ -#define FOLL_LONGTERM 0x10000 /* mapping lifetime is indefinite: see below */ -#define FOLL_SPLIT_PMD 0x20000 /* split huge pmd before returning */ -#define FOLL_PIN 0x40000 /* pages must be released via unpin_user_page */ -#define FOLL_FAST_ONLY 0x80000 /* gup_fast: prevent fall-back to slow gup */ - -/* - * FOLL_PIN and FOLL_LONGTERM may be used in various combinations with each - * other. Here is what they mean, and how to use them: - * - * FOLL_LONGTERM indicates that the page will be held for an indefinite time - * period _often_ under userspace control. This is in contrast to - * iov_iter_get_pages(), whose usages are transient. - * - * FIXME: For pages which are part of a filesystem, mappings are subject to the - * lifetime enforced by the filesystem and we need guarantees that longterm - * users like RDMA and V4L2 only establish mappings which coordinate usage with - * the filesystem. Ideas for this coordination include revoking the longterm - * pin, delaying writeback, bounce buffer page writeback, etc. As FS DAX was - * added after the problem with filesystems was found FS DAX VMAs are - * specifically failed. Filesystem pages are still subject to bugs and use of - * FOLL_LONGTERM should be avoided on those pages. - * - * FIXME: Also NOTE that FOLL_LONGTERM is not supported in every GUP call. - * Currently only get_user_pages() and get_user_pages_fast() support this flag - * and calls to get_user_pages_[un]locked are specifically not allowed. This - * is due to an incompatibility with the FS DAX check and - * FAULT_FLAG_ALLOW_RETRY. - * - * In the CMA case: long term pins in a CMA region would unnecessarily fragment - * that region. And so, CMA attempts to migrate the page before pinning, when - * FOLL_LONGTERM is specified. - * - * FOLL_PIN indicates that a special kind of tracking (not just page->_refcount, - * but an additional pin counting system) will be invoked. This is intended for - * anything that gets a page reference and then touches page data (for example, - * Direct IO). This lets the filesystem know that some non-file-system entity is - * potentially changing the pages' data. In contrast to FOLL_GET (whose pages - * are released via put_page()), FOLL_PIN pages must be released, ultimately, by - * a call to unpin_user_page(). - * - * FOLL_PIN is similar to FOLL_GET: both of these pin pages. They use different - * and separate refcounting mechanisms, however, and that means that each has - * its own acquire and release mechanisms: - * - * FOLL_GET: get_user_pages*() to acquire, and put_page() to release. - * - * FOLL_PIN: pin_user_pages*() to acquire, and unpin_user_pages to release. - * - * FOLL_PIN and FOLL_GET are mutually exclusive for a given function call. - * (The underlying pages may experience both FOLL_GET-based and FOLL_PIN-based - * calls applied to them, and that's perfectly OK. This is a constraint on the - * callers, not on the pages.) - * - * FOLL_PIN should be set internally by the pin_user_pages*() APIs, never - * directly by the caller. That's in order to help avoid mismatches when - * releasing pages: get_user_pages*() pages must be released via put_page(), - * while pin_user_pages*() pages must be released via unpin_user_page(). - * - * Please see Documentation/core-api/pin_user_pages.rst for more information. - */ - static inline int vm_fault_to_errno(vm_fault_t vm_fault, int foll_flags) { if (vm_fault & VM_FAULT_OOM) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 500e536796ca..0c80a5ad6e6a 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -1003,4 +1003,77 @@ enum fault_flag { typedef unsigned int __bitwise zap_flags_t; +/* + * FOLL_PIN and FOLL_LONGTERM may be used in various combinations with each + * other. Here is what they mean, and how to use them: + * + * FOLL_LONGTERM indicates that the page will be held for an indefinite time + * period _often_ under userspace control. This is in contrast to + * iov_iter_get_pages(), whose usages are transient. + * + * FIXME: For pages which are part of a filesystem, mappings are subject to the + * lifetime enforced by the filesystem and we need guarantees that longterm + * users like RDMA and V4L2 only establish mappings which coordinate usage with + * the filesystem. Ideas for this coordination include revoking the longterm + * pin, delaying writeback, bounce buffer page writeback, etc. As FS DAX was + * added after the problem with filesystems was found FS DAX VMAs are + * specifically failed. Filesystem pages are still subject to bugs and use of + * FOLL_LONGTERM should be avoided on those pages. + * + * FIXME: Also NOTE that FOLL_LONGTERM is not supported in every GUP call. + * Currently only get_user_pages() and get_user_pages_fast() support this flag + * and calls to get_user_pages_[un]locked are specifically not allowed. This + * is due to an incompatibility with the FS DAX check and + * FAULT_FLAG_ALLOW_RETRY. + * + * In the CMA case: long term pins in a CMA region would unnecessarily fragment + * that region. And so, CMA attempts to migrate the page before pinning, when + * FOLL_LONGTERM is specified. + * + * FOLL_PIN indicates that a special kind of tracking (not just page->_refcount, + * but an additional pin counting system) will be invoked. This is intended for + * anything that gets a page reference and then touches page data (for example, + * Direct IO). This lets the filesystem know that some non-file-system entity is + * potentially changing the pages' data. In contrast to FOLL_GET (whose pages + * are released via put_page()), FOLL_PIN pages must be released, ultimately, by + * a call to unpin_user_page(). + * + * FOLL_PIN is similar to FOLL_GET: both of these pin pages. They use different + * and separate refcounting mechanisms, however, and that means that each has + * its own acquire and release mechanisms: + * + * FOLL_GET: get_user_pages*() to acquire, and put_page() to release. + * + * FOLL_PIN: pin_user_pages*() to acquire, and unpin_user_pages to release. + * + * FOLL_PIN and FOLL_GET are mutually exclusive for a given function call. + * (The underlying pages may experience both FOLL_GET-based and FOLL_PIN-based + * calls applied to them, and that's perfectly OK. This is a constraint on the + * callers, not on the pages.) + * + * FOLL_PIN should be set internally by the pin_user_pages*() APIs, never + * directly by the caller. That's in order to help avoid mismatches when + * releasing pages: get_user_pages*() pages must be released via put_page(), + * while pin_user_pages*() pages must be released via unpin_user_page(). + * + * Please see Documentation/core-api/pin_user_pages.rst for more information. + */ +#define FOLL_WRITE 0x01 /* check pte is writable */ +#define FOLL_TOUCH 0x02 /* mark page accessed */ +#define FOLL_GET 0x04 /* do get_page on page */ +#define FOLL_DUMP 0x08 /* give error on hole if it would be zero */ +#define FOLL_FORCE 0x10 /* get_user_pages read/write w/o permission */ +#define FOLL_NOWAIT 0x20 /* if a disk transfer is needed, start the IO + * and return without waiting upon it */ +#define FOLL_NOFAULT 0x80 /* do not fault in pages */ +#define FOLL_HWPOISON 0x100 /* check page is hwpoisoned */ +#define FOLL_MIGRATION 0x400 /* wait for page to replace migration entry */ +#define FOLL_TRIED 0x800 /* a retry, previous pass started an IO */ +#define FOLL_REMOTE 0x2000 /* we are working on non-current tsk/mm */ +#define FOLL_ANON 0x8000 /* don't do file mappings */ +#define FOLL_LONGTERM 0x10000 /* mapping lifetime is indefinite: see below */ +#define FOLL_SPLIT_PMD 0x20000 /* split huge pmd before returning */ +#define FOLL_PIN 0x40000 /* pages must be released via unpin_user_page */ +#define FOLL_FAST_ONLY 0x80000 /* gup_fast: prevent fall-back to slow gup */ + #endif /* _LINUX_MM_TYPES_H */ From patchwork Tue Nov 1 16:30:57 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Howells X-Patchwork-Id: 13032481 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 88C51C4332F for ; Tue, 1 Nov 2022 17:00:22 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 2C6486B0074; Tue, 1 Nov 2022 13:00:22 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 24DEC8E0002; Tue, 1 Nov 2022 13:00:22 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0C8298E0001; Tue, 1 Nov 2022 13:00:22 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id E8CE66B0074 for ; Tue, 1 Nov 2022 13:00:21 -0400 (EDT) Received: from smtpin14.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 78EBCAB841 for ; Tue, 1 Nov 2022 17:00:21 +0000 (UTC) X-FDA: 80085486642.14.817CBA1 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf15.hostedemail.com (Postfix) with ESMTP id 1C2DAA0015 for ; Tue, 1 Nov 2022 17:00:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1667322018; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding:resent-to: resent-from:resent-message-id:in-reply-to:in-reply-to: references:references; bh=lCaciGNF/yGmehdlbXyPJAuWY6OahIbalppz5X6xCwU=; b=AhQPuA9OOjnhfK0G1VPRZRVvmFOkZfKNi8x7qyJg0BQxFf37jn7QuOtcqN6WOzX9zRoUQ3 8grJuaHXe3K8WWQLuP5Kt9/yxvHUSVpybiRIrCSFniB52gc80XRyol+92mAAwaMW3jG3F1 j1CGS0lkoYIHexb58vGBQgabJqrLQDA= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-94-vCW1APMHNJeghPfv2oEroQ-1; Tue, 01 Nov 2022 13:00:15 -0400 X-MC-Unique: vCW1APMHNJeghPfv2oEroQ-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 718121C0A10D for ; Tue, 1 Nov 2022 17:00:15 +0000 (UTC) Received: from warthog.procyon.org.uk (unknown [10.33.36.73]) by smtp.corp.redhat.com (Postfix) with ESMTP id 08D26468A41 for ; Tue, 1 Nov 2022 17:00:14 +0000 (UTC) X-Mailbox-Line: From dhowells Tue Nov 1 16: 31:32 2022 Received: from imap.gmail.com [2a00:1450:400c:c00::6d] by warthog.procyon.org.uk with IMAP (fetchmail-7.0.0-alpha9) for (single-drop); Tue, 01 Nov 2022 16:31:32 +0000 (GMT) Received: by 2002:ac0:c78e:0:0:0:0:0 with SMTP id j14csp1842936imk; Tue, 1 Nov 2022 09:31:06 -0700 (PDT) X-Google-Smtp-Source: AMsMyM5OXVseiP7Uwj3ICWj1kwhsz6h6Z45qVnsdcRHNFZ5ChHR6IqN6WL7gQC5skYB3ybmLBcwq X-Received: by 2002:ac8:58c2:0:b0:398:f5c4:9bed with SMTP id u2-20020ac858c2000000b00398f5c49bedmr15502957qta.367.1667320266241; Tue, 01 Nov 2022 09:31:06 -0700 (PDT) Received: from us-smtp-1.mimecast.com (us-smtp-2.mimecast.com. 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Registered in England and Wales under Company Registration No. 3798903 Subject: [RFC PATCH 02/12] iov_iter: Add a function to extract a page list from an iterator From: David Howells To: Steve French , Al Viro Cc: Christoph Hellwig , John Hubbard , Matthew Wilcox , linux-fsdevel@vger.kernel.org, linux-mm@vger.kernel.org, dhowells@redhat.com, Shyam Prasad N , Rohith Surabattula , Tom Talpey , Christoph Hellwig , Matthew Wilcox , Jeff Layton , linux-cifs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Date: Tue, 01 Nov 2022 16:30:57 +0000 Message-ID: <166732025748.3186319.8314014902727092626.stgit@warthog.procyon.org.uk> In-Reply-To: <166732024173.3186319.18204305072070871546.stgit@warthog.procyon.org.uk> References: <166732024173.3186319.18204305072070871546.stgit@warthog.procyon.org.uk> User-Agent: StGit/1.5 MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1667322019; a=rsa-sha256; cv=none; b=Z0AMIPFa2RvE5Q8nft0sdVThmD+bLfX57elGT6Jph63RPlRaBdzhF6qx2kgLVrvzqKJN0u RV7OK8XqzJsHztnHhZ3k0aK7x0gN7d4t3/leB7H5zxDVXkJ7S/cX5ZZvOmCRdcfma+oQuw sUuVcnE/TiOvFe0aV5b+LsF2t9gmQHY= ARC-Authentication-Results: i=1; imf15.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=AhQPuA9O; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf15.hostedemail.com: domain of dhowells@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=dhowells@redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1667322019; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding:resent-to: resent-from:resent-message-id:in-reply-to:in-reply-to: references:references:dkim-signature; bh=lCaciGNF/yGmehdlbXyPJAuWY6OahIbalppz5X6xCwU=; b=guJkXVSCtSox0oMcbGxK8MkAjilZyg5Ofh8z2niVvnhnCQ2XLp8OYo/49wziONUkIC5bho Kq3FD8VkS3UBvb6dO/95OLiwUf2ljXiTtPVNk+4bFfkfenQDmGPCbJeZZwHNfORHDTfWgx 74DWITaPU00sVmg3ChlHSj54Deg7zAA= X-Stat-Signature: wou91zx3pc94bto6eyxibcq8e3y9bbgg X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 1C2DAA0015 X-Rspam-User: Authentication-Results: imf15.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=AhQPuA9O; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf15.hostedemail.com: domain of dhowells@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=dhowells@redhat.com X-HE-Tag: 1667322018-976215 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: Add a function, iov_iter_extract_pages(), to extract a list of pages from an iterator. The pages may be returned with a reference added or a pin added or neither, depending on the type of iterator and the direction of transfer. An additional function, iov_iter_extract_mode() is also provided so that the mode of retention that will be employed for an iterator can be queried - and therefore how the caller should dispose of the pages later. There are three cases: (1) Transfer *into* an ITER_IOVEC or ITER_UBUF iterator. Extracted pages will have pins obtained on them (but not references) so that fork() doesn't CoW the pages incorrectly whilst the I/O is in progress. iov_iter_extract_mode() will return FOLL_PIN for this case. The caller should use something like unpin_user_page() to dispose of the page. (2) Transfer is *out of* an ITER_IOVEC or ITER_UBUF iterator. Extracted pages will have references obtained on them, but not pins. iov_iter_extract_mode() will return FOLL_GET. The caller should use something like put_page() for page disposal. (3) Any other sort of iterator. No refs or pins are obtained on the page, the assumption is made that the caller will manage page retention. iov_iter_extract_mode() will return 0. The pages don't need additional disposal. Signed-off-by: David Howells cc: Al Viro cc: Christoph Hellwig cc: John Hubbard cc: Matthew Wilcox cc: linux-fsdevel@vger.kernel.org cc: linux-mm@vger.kernel.org Link: https://lore.kernel.org/r/166722777971.2555743.12953624861046741424.stgit@warthog.procyon.org.uk/ --- include/linux/uio.h | 29 ++++ lib/iov_iter.c | 333 +++++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 362 insertions(+) diff --git a/include/linux/uio.h b/include/linux/uio.h index 87fc3d0dda98..fa5c9a722b42 100644 --- a/include/linux/uio.h +++ b/include/linux/uio.h @@ -354,4 +354,33 @@ static inline void iov_iter_ubuf(struct iov_iter *i, unsigned int direction, }; } +ssize_t iov_iter_extract_pages(struct iov_iter *i, struct page ***pages, + size_t maxsize, unsigned int maxpages, + size_t *offset0); + +/** + * iov_iter_extract_mode - Indicate how pages from the iterator will be retained + * @iter: The iterator + * + * Examine the indicator and indicate with FOLL_PIN, FOLL_GET or 0 as to how, + * if at all, pages extracted from the iterator will be retained by the + * extraction function. + * + * FOLL_GET indicates that the pages will have a reference taken on them that + * the caller must put. This can be done for DMA/async DIO write from a page. + * + * FOLL_PIN indicates that the pages will have a pin placed in them that the + * caller must unpin. This is must be done for DMA/async DIO read to a page to + * avoid CoW problems in fork. + * + * 0 indicates that no measures are taken and that it's up to the caller to + * retain the pages. + */ +static inline unsigned int iov_iter_extract_mode(struct iov_iter *iter) +{ + if (user_backed_iter(iter)) + return iter->data_source ? FOLL_GET : FOLL_PIN; + return 0; +} + #endif diff --git a/lib/iov_iter.c b/lib/iov_iter.c index 98e8425b060d..96bfb117f19a 100644 --- a/lib/iov_iter.c +++ b/lib/iov_iter.c @@ -1898,3 +1898,336 @@ void iov_iter_restore(struct iov_iter *i, struct iov_iter_state *state) i->iov -= state->nr_segs - i->nr_segs; i->nr_segs = state->nr_segs; } + +/* + * Extract a list of contiguous pages from an ITER_PIPE iterator. This does + * not get references of its own on the pages, nor does it get a pin on them. + * If there's a partial page, it adds that first and will then allocate and add + * pages into the pipe to make up the buffer space to the amount required. + * + * The caller must hold the pipe locked and only transferring into a pipe is + * supported. + */ +static ssize_t iov_iter_extract_pipe_pages(struct iov_iter *i, + struct page ***pages, size_t maxsize, + unsigned int maxpages, + size_t *offset0) +{ + unsigned int nr, offset, chunk, j; + struct page **p; + size_t left; + + if (!sanity(i)) + return -EFAULT; + + offset = pipe_npages(i, &nr); + if (!nr) + return -EFAULT; + *offset0 = offset; + + maxpages = min_t(size_t, nr, maxpages); + maxpages = want_pages_array(pages, maxsize, offset, maxpages); + if (!maxpages) + return -ENOMEM; + p = *pages; + + left = maxsize; + for (j = 0; j < maxpages; j++) { + struct page *page = append_pipe(i, left, &offset); + if (!page) + break; + chunk = min_t(size_t, left, PAGE_SIZE - offset); + left -= chunk; + *p++ = page; + } + if (!j) + return -EFAULT; + return maxsize - left; +} + +/* + * Extract a list of contiguous pages from an ITER_XARRAY iterator. This does not + * get references on the pages, nor does it get a pin on them. + */ +static ssize_t iov_iter_extract_xarray_pages(struct iov_iter *i, + struct page ***pages, size_t maxsize, + unsigned int maxpages, + size_t *offset0) +{ + struct page *page, **p; + unsigned int nr = 0, offset; + loff_t pos = i->xarray_start + i->iov_offset; + pgoff_t index = pos >> PAGE_SHIFT; + XA_STATE(xas, i->xarray, index); + + offset = pos & ~PAGE_MASK; + *offset0 = offset; + + maxpages = want_pages_array(pages, maxsize, offset, maxpages); + if (!maxpages) + return -ENOMEM; + p = *pages; + + rcu_read_lock(); + for (page = xas_load(&xas); page; page = xas_next(&xas)) { + if (xas_retry(&xas, page)) + continue; + + /* Has the page moved or been split? */ + if (unlikely(page != xas_reload(&xas))) { + xas_reset(&xas); + continue; + } + + p[nr++] = find_subpage(page, xas.xa_index); + if (nr == maxpages) + break; + } + rcu_read_unlock(); + + maxsize = min_t(size_t, nr * PAGE_SIZE - offset, maxsize); + i->iov_offset += maxsize; + i->count -= maxsize; + return maxsize; +} + +/* + * Extract a list of contiguous pages from an ITER_BVEC iterator. This does + * not get references on the pages, nor does it get a pin on them. + */ +static ssize_t iov_iter_extract_bvec_pages(struct iov_iter *i, + struct page ***pages, size_t maxsize, + unsigned int maxpages, + size_t *offset0) +{ + struct page **p, *page; + size_t skip = i->iov_offset, offset; + int k; + + maxsize = min(maxsize, i->bvec->bv_len - skip); + skip += i->bvec->bv_offset; + page = i->bvec->bv_page + skip / PAGE_SIZE; + offset = skip % PAGE_SIZE; + *offset0 = offset; + + maxpages = want_pages_array(pages, maxsize, offset, maxpages); + if (!maxpages) + return -ENOMEM; + p = *pages; + for (k = 0; k < maxpages; k++) + p[k] = page + k; + + maxsize = min_t(size_t, maxsize, maxpages * PAGE_SIZE - offset); + i->count -= maxsize; + i->iov_offset += maxsize; + if (i->iov_offset == i->bvec->bv_len) { + i->iov_offset = 0; + i->bvec++; + i->nr_segs--; + } + return maxsize; +} + +/* + * Get the first segment from an ITER_UBUF or ITER_IOVEC iterator. The + * iterator must not be empty. + */ +static unsigned long iov_iter_extract_first_user_segment(const struct iov_iter *i, + size_t *size) +{ + size_t skip; + long k; + + if (iter_is_ubuf(i)) + return (unsigned long)i->ubuf + i->iov_offset; + + for (k = 0, skip = i->iov_offset; k < i->nr_segs; k++, skip = 0) { + size_t len = i->iov[k].iov_len - skip; + + if (unlikely(!len)) + continue; + if (*size > len) + *size = len; + return (unsigned long)i->iov[k].iov_base + skip; + } + BUG(); // if it had been empty, we wouldn't get called +} + +/* + * Extract a list of contiguous pages from a user iterator and get references + * on them. This should only be used iff the iterator is user-backed + * (IOBUF/UBUF) and data is being transferred out of the buffer described by + * the iterator (ie. this is the source). + * + * The pages are returned with incremented refcounts that the caller must undo + * once the transfer is complete, but no additional pins are obtained. + * + * This is only safe to be used where background IO/DMA is not going to be + * modifying the buffer, and so won't cause a problem with CoW on fork. + */ +static ssize_t iov_iter_extract_user_pages_and_get(struct iov_iter *i, + struct page ***pages, + size_t maxsize, + unsigned int maxpages, + size_t *offset0) +{ + unsigned long addr; + unsigned int gup_flags = FOLL_GET; + size_t offset; + int res; + + if (WARN_ON_ONCE(iov_iter_rw(i) != WRITE)) + return -EFAULT; + + if (i->nofault) + gup_flags |= FOLL_NOFAULT; + + addr = iov_iter_extract_first_user_segment(i, &maxsize); + *offset0 = offset = addr % PAGE_SIZE; + addr &= PAGE_MASK; + maxpages = want_pages_array(pages, maxsize, offset, maxpages); + if (!maxpages) + return -ENOMEM; + res = get_user_pages_fast(addr, maxpages, gup_flags, *pages); + if (unlikely(res <= 0)) + return res; + maxsize = min_t(size_t, maxsize, res * PAGE_SIZE - offset); + iov_iter_advance(i, maxsize); + return maxsize; +} + +/* + * Extract a list of contiguous pages from a user iterator and get a pin on + * each of them. This should only be used iff the iterator is user-backed + * (IOBUF/UBUF) and data is being transferred into the buffer described by the + * iterator (ie. this is the destination). + * + * It does not get refs on the pages, but the pages must be unpinned by the + * caller once the transfer is complete. + * + * This is safe to be used where background IO/DMA *is* going to be modifying + * the buffer; using a pin rather than a ref makes sure that CoW happens + * correctly in the parent during fork. + */ +static ssize_t iov_iter_extract_user_pages_and_pin(struct iov_iter *i, + struct page ***pages, + size_t maxsize, + unsigned int maxpages, + size_t *offset0) +{ + unsigned long addr; + unsigned int gup_flags = FOLL_PIN | FOLL_WRITE; + size_t offset; + int res; + + if (WARN_ON_ONCE(iov_iter_rw(i) != READ)) + return -EFAULT; + + if (i->nofault) + gup_flags |= FOLL_NOFAULT; + + addr = first_iovec_segment(i, &maxsize); + *offset0 = offset = addr % PAGE_SIZE; + addr &= PAGE_MASK; + maxpages = want_pages_array(pages, maxsize, offset, maxpages); + if (!maxpages) + return -ENOMEM; + res = pin_user_pages_fast(addr, maxpages, gup_flags, *pages); + if (unlikely(res <= 0)) + return res; + maxsize = min_t(size_t, maxsize, res * PAGE_SIZE - offset); + iov_iter_advance(i, maxsize); + return maxsize; +} + +static ssize_t iov_iter_extract_user_pages(struct iov_iter *i, + struct page ***pages, size_t maxsize, + unsigned int maxpages, + size_t *offset0) +{ + switch (iov_iter_extract_mode(i)) { + case FOLL_GET: + return iov_iter_extract_user_pages_and_get(i, pages, maxsize, + maxpages, offset0); + case FOLL_PIN: + return iov_iter_extract_user_pages_and_pin(i, pages, maxsize, + maxpages, offset0); + default: + BUG(); + } +} + +/** + * iov_iter_extract_pages - Extract a list of contiguous pages from an iterator + * @i: The iterator to extract from + * @pages: Where to return the list of pages + * @maxsize: The maximum amount of iterator to extract + * @maxpages: The maximum size of the list of pages + * @offset0: Where to return the starting offset into (*@pages)[0] + * + * Extract a list of contiguous pages from the current point of the iterator, + * advancing the iterator. The maximum number of pages and the maximum amount + * of page contents can be set. + * + * If *@pages is NULL, a page list will be allocated to the required size and + * *@pages will be set to its base. If *@pages is not NULL, it will be assumed + * that the caller allocated a page list at least @maxpages in size and this + * will be filled in. + * + * Extra refs or pins on the pages may be obtained as follows: + * + * (*) If the iterator is user-backed (ITER_IOVEC/ITER_UBUF) and data is to be + * transferred /OUT OF/ the described buffer, refs will be taken on the + * pages, but pins will not be added. This can be used for DMA from a + * page; it cannot be used for DMA to a page, as it may cause page-COW + * problems in fork. + * + * (*) If the iterator is user-backed (ITER_IOVEC/ITER_UBUF) and data is to be + * transferred /INTO/ the described buffer, pins will be added to the + * pages, but refs will not be taken. This must be used for DMA to a + * page. + * + * (*) If the iterator is ITER_PIPE, this must describe a destination for the + * data. Additional pages may be allocated and added to the pipe (which + * will hold the refs), but neither refs nor pins will be obtained for the + * caller. The caller must hold the pipe lock. + * + * (*) If the iterator is ITER_BVEC or ITER_XARRAY, the pages are merely + * listed; no extra refs or pins are obtained. + * + * Note also: + * + * (*) Use with ITER_KVEC is not supported as that may refer to memory that + * doesn't have associated page structs. + * + * (*) Use with ITER_DISCARD is not supported as that has no content. + * + * On success, the function sets *@pages to the new pagelist, if allocated, and + * sets *offset0 to the offset into the first page and returns the amount of + * buffer space added represented by the page list. + * + * It may also return -ENOMEM and -EFAULT. + */ +ssize_t iov_iter_extract_pages(struct iov_iter *i, struct page ***pages, + size_t maxsize, unsigned int maxpages, + size_t *offset0) +{ + maxsize = min3(maxsize, i->count, MAX_RW_COUNT); + if (!maxsize) + return 0; + + if (likely(user_backed_iter(i))) + return iov_iter_extract_user_pages(i, pages, maxsize, + maxpages, offset0); + if (iov_iter_is_bvec(i)) + return iov_iter_extract_bvec_pages(i, pages, maxsize, + maxpages, offset0); + if (iov_iter_is_pipe(i)) + return iov_iter_extract_pipe_pages(i, pages, maxsize, + maxpages, offset0); + if (iov_iter_is_xarray(i)) + return iov_iter_extract_xarray_pages(i, pages, maxsize, + maxpages, offset0); + return -EFAULT; +} +EXPORT_SYMBOL(iov_iter_extract_pages);