From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8C51DC433DF for ; Fri, 29 May 2020 23:43:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 648A320897 for ; Fri, 29 May 2020 23:43:35 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=nvidia.com header.i=@nvidia.com header.b="aLSQsNOd" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728554AbgE2XnN (ORCPT ); Fri, 29 May 2020 19:43:13 -0400 Received: from hqnvemgate24.nvidia.com ([216.228.121.143]:4263 "EHLO hqnvemgate24.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727876AbgE2XnM (ORCPT ); Fri, 29 May 2020 19:43:12 -0400 Received: from hqpgpgate102.nvidia.com (Not Verified[216.228.121.13]) by hqnvemgate24.nvidia.com (using TLS: TLSv1.2, DES-CBC3-SHA) id ; Fri, 29 May 2020 16:41:39 -0700 Received: from hqmail.nvidia.com ([172.20.161.6]) by hqpgpgate102.nvidia.com (PGP Universal service); Fri, 29 May 2020 16:43:11 -0700 X-PGP-Universal: processed; by hqpgpgate102.nvidia.com on Fri, 29 May 2020 16:43:11 -0700 Received: from HQMAIL109.nvidia.com (172.20.187.15) by HQMAIL101.nvidia.com (172.20.187.10) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Fri, 29 May 2020 23:43:11 +0000 Received: from hqnvemgw03.nvidia.com (10.124.88.68) by HQMAIL109.nvidia.com (172.20.187.15) with Microsoft SMTP Server (TLS) id 15.0.1473.3 via Frontend Transport; Fri, 29 May 2020 23:43:11 +0000 Received: from sandstorm.nvidia.com (Not Verified[10.2.87.173]) by hqnvemgw03.nvidia.com with Trustwave SEG (v7,5,8,10121) id ; Fri, 29 May 2020 16:43:11 -0700 From: John Hubbard To: Andrew Morton CC: "Michael S . Tsirkin" , Jason Wang , Vlastimil Babka , =?UTF-8?q?J=C3=A9r=C3=B4me=20Glisse?= , Jan Kara , Dave Chinner , Souptick Joarder , Jonathan Corbet , , , , , , LKML , , John Hubbard Subject: [PATCH 1/2] docs: mm/gup: pin_user_pages.rst: add a "case 5" Date: Fri, 29 May 2020 16:43:08 -0700 Message-ID: <20200529234309.484480-2-jhubbard@nvidia.com> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200529234309.484480-1-jhubbard@nvidia.com> References: <20200529234309.484480-1-jhubbard@nvidia.com> MIME-Version: 1.0 X-NVConfidentiality: public Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1590795699; bh=/rPFi6UMeQqIwH0AXw3mk+tI0oUReiPuYz0u4gk+gB4=; h=X-PGP-Universal:From:To:CC:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:X-NVConfidentiality: Content-Type:Content-Transfer-Encoding; b=aLSQsNOdMWIF0LkIlbgwkwE7Tydi/7c5/ubijb8BcaFTIZEmhASKRET9Pca2eBhxG dREVJpcO2ADpj3UkVt0jUxkcnrRTCw4rXg9IKomdo4dQTH1CfYYB8ffwCmWCd9HN3A JIWv3bqa+Gg3EHmOTKcmCEuIvUL/VqJY25SULLKbpwSQ6b1XwGVe3sAYTL/Qwlabih x607bsQ0F1z2uQFX8AL5YzbsWkdWeUT/F0Jb8Ib1qqB0Pn0XVtAfJaEZQDl8GkPKcN TFCHCxL5GeGK/stqfrP64DTXAMPgO0H6TJzbyusWRjhSQfHOqkJ1IE/IVGf3B5XjlI 4QyQIJBypY8RA== Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org There are four cases listed in pin_user_pages.rst. These are intended to help developers figure out whether to use get_user_pages*(), or pin_user_pages*(). However, the four cases do not cover all the situations. For example, drivers/vhost/vhost.c has a "pin, write to page, set page dirty, unpin" case. Add a fifth case, to help explain that there is a general pattern that requires pin_user_pages*() API calls. Cc: Vlastimil Babka Cc: Jan Kara Cc: J=C3=A9r=C3=B4me Glisse Cc: Dave Chinner Cc: Jonathan Corbet Cc: linux-doc@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org Signed-off-by: John Hubbard --- Documentation/core-api/pin_user_pages.rst | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) diff --git a/Documentation/core-api/pin_user_pages.rst b/Documentation/core= -api/pin_user_pages.rst index 4675b04e8829..b9f2688a2c67 100644 --- a/Documentation/core-api/pin_user_pages.rst +++ b/Documentation/core-api/pin_user_pages.rst @@ -171,6 +171,26 @@ If only struct page data (as opposed to the actual mem= ory contents that a page is tracking) is affected, then normal GUP calls are sufficient, and neithe= r flag needs to be set. =20 +CASE 5: Pinning in order to write to the data within the page +------------------------------------------------------------- +Even though neither DMA nor Direct IO is involved, just a simple case of "= pin, +access page's data, unpin" can cause a problem. Case 5 may be considered a +superset of Case 1, plus Case 2, plus anything that invokes that pattern. = In +other words, if the code is neither Case 1 nor Case 2, it may still requir= e +FOLL_PIN, for patterns like this: + +Correct (uses FOLL_PIN calls): + pin_user_pages() + access the data within the pages + set_page_dirty_lock() + unpin_user_pages() + +INCORRECT (uses FOLL_GET calls): + get_user_pages() + access the data within the pages + set_page_dirty_lock() + put_page() + page_maybe_dma_pinned(): the whole point of pinning =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D =20 --=20 2.26.2 From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Hubbard Subject: [PATCH 1/2] docs: mm/gup: pin_user_pages.rst: add a "case 5" Date: Fri, 29 May 2020 16:43:08 -0700 Message-ID: <20200529234309.484480-2-jhubbard@nvidia.com> References: <20200529234309.484480-1-jhubbard@nvidia.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: In-Reply-To: <20200529234309.484480-1-jhubbard@nvidia.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" To: Andrew Morton Cc: Jan Kara , linux-doc@vger.kernel.org, kvm@vger.kernel.org, "Michael S . Tsirkin" , netdev@vger.kernel.org, Jonathan Corbet , Dave Chinner , LKML , virtualization@lists.linux-foundation.org, linux-mm@kvack.org, =?UTF-8?q?J=C3=A9r=C3=B4me=20Glisse?= , Souptick Joarder , John Hubbard , linux-fsdevel@vger.kernel.org, Vlastimil Babka List-Id: virtualization@lists.linuxfoundation.org VGhlcmUgYXJlIGZvdXIgY2FzZXMgbGlzdGVkIGluIHBpbl91c2VyX3BhZ2VzLnJzdC4gVGhlc2Ug YXJlCmludGVuZGVkIHRvIGhlbHAgZGV2ZWxvcGVycyBmaWd1cmUgb3V0IHdoZXRoZXIgdG8gdXNl CmdldF91c2VyX3BhZ2VzKigpLCBvciBwaW5fdXNlcl9wYWdlcyooKS4gSG93ZXZlciwgdGhlIGZv dXIgY2FzZXMKZG8gbm90IGNvdmVyIGFsbCB0aGUgc2l0dWF0aW9ucy4gRm9yIGV4YW1wbGUsIGRy aXZlcnMvdmhvc3Qvdmhvc3QuYwpoYXMgYSAicGluLCB3cml0ZSB0byBwYWdlLCBzZXQgcGFnZSBk aXJ0eSwgdW5waW4iIGNhc2UuCgpBZGQgYSBmaWZ0aCBjYXNlLCB0byBoZWxwIGV4cGxhaW4gdGhh dCB0aGVyZSBpcyBhIGdlbmVyYWwgcGF0dGVybgp0aGF0IHJlcXVpcmVzIHBpbl91c2VyX3BhZ2Vz KigpIEFQSSBjYWxscy4KCkNjOiBWbGFzdGltaWwgQmFia2EgPHZiYWJrYUBzdXNlLmN6PgpDYzog SmFuIEthcmEgPGphY2tAc3VzZS5jej4KQ2M6IErDqXLDtG1lIEdsaXNzZSA8amdsaXNzZUByZWRo YXQuY29tPgpDYzogRGF2ZSBDaGlubmVyIDxkYXZpZEBmcm9tb3JiaXQuY29tPgpDYzogSm9uYXRo YW4gQ29yYmV0IDxjb3JiZXRAbHduLm5ldD4KQ2M6IGxpbnV4LWRvY0B2Z2VyLmtlcm5lbC5vcmcK Q2M6IGxpbnV4LWZzZGV2ZWxAdmdlci5rZXJuZWwub3JnClNpZ25lZC1vZmYtYnk6IEpvaG4gSHVi YmFyZCA8amh1YmJhcmRAbnZpZGlhLmNvbT4KLS0tCiBEb2N1bWVudGF0aW9uL2NvcmUtYXBpL3Bp bl91c2VyX3BhZ2VzLnJzdCB8IDIwICsrKysrKysrKysrKysrKysrKysrCiAxIGZpbGUgY2hhbmdl ZCwgMjAgaW5zZXJ0aW9ucygrKQoKZGlmZiAtLWdpdCBhL0RvY3VtZW50YXRpb24vY29yZS1hcGkv cGluX3VzZXJfcGFnZXMucnN0IGIvRG9jdW1lbnRhdGlvbi9jb3JlLWFwaS9waW5fdXNlcl9wYWdl cy5yc3QKaW5kZXggNDY3NWIwNGU4ODI5Li5iOWYyNjg4YTJjNjcgMTAwNjQ0Ci0tLSBhL0RvY3Vt ZW50YXRpb24vY29yZS1hcGkvcGluX3VzZXJfcGFnZXMucnN0CisrKyBiL0RvY3VtZW50YXRpb24v Y29yZS1hcGkvcGluX3VzZXJfcGFnZXMucnN0CkBAIC0xNzEsNiArMTcxLDI2IEBAIElmIG9ubHkg c3RydWN0IHBhZ2UgZGF0YSAoYXMgb3Bwb3NlZCB0byB0aGUgYWN0dWFsIG1lbW9yeSBjb250ZW50 cyB0aGF0IGEgcGFnZQogaXMgdHJhY2tpbmcpIGlzIGFmZmVjdGVkLCB0aGVuIG5vcm1hbCBHVVAg Y2FsbHMgYXJlIHN1ZmZpY2llbnQsIGFuZCBuZWl0aGVyIGZsYWcKIG5lZWRzIHRvIGJlIHNldC4K IAorQ0FTRSA1OiBQaW5uaW5nIGluIG9yZGVyIHRvIHdyaXRlIHRvIHRoZSBkYXRhIHdpdGhpbiB0 aGUgcGFnZQorLS0tLS0tLS0tLS0tLS0tLS0tLS0tLS0tLS0tLS0tLS0tLS0tLS0tLS0tLS0tLS0t LS0tLS0tLS0tLS0tLQorRXZlbiB0aG91Z2ggbmVpdGhlciBETUEgbm9yIERpcmVjdCBJTyBpcyBp bnZvbHZlZCwganVzdCBhIHNpbXBsZSBjYXNlIG9mICJwaW4sCithY2Nlc3MgcGFnZSdzIGRhdGEs IHVucGluIiBjYW4gY2F1c2UgYSBwcm9ibGVtLiBDYXNlIDUgbWF5IGJlIGNvbnNpZGVyZWQgYQor c3VwZXJzZXQgb2YgQ2FzZSAxLCBwbHVzIENhc2UgMiwgcGx1cyBhbnl0aGluZyB0aGF0IGludm9r ZXMgdGhhdCBwYXR0ZXJuLiBJbgorb3RoZXIgd29yZHMsIGlmIHRoZSBjb2RlIGlzIG5laXRoZXIg Q2FzZSAxIG5vciBDYXNlIDIsIGl0IG1heSBzdGlsbCByZXF1aXJlCitGT0xMX1BJTiwgZm9yIHBh dHRlcm5zIGxpa2UgdGhpczoKKworQ29ycmVjdCAodXNlcyBGT0xMX1BJTiBjYWxscyk6CisgICAg cGluX3VzZXJfcGFnZXMoKQorICAgIGFjY2VzcyB0aGUgZGF0YSB3aXRoaW4gdGhlIHBhZ2VzCisg ICAgc2V0X3BhZ2VfZGlydHlfbG9jaygpCisgICAgdW5waW5fdXNlcl9wYWdlcygpCisKK0lOQ09S UkVDVCAodXNlcyBGT0xMX0dFVCBjYWxscyk6CisgICAgZ2V0X3VzZXJfcGFnZXMoKQorICAgIGFj Y2VzcyB0aGUgZGF0YSB3aXRoaW4gdGhlIHBhZ2VzCisgICAgc2V0X3BhZ2VfZGlydHlfbG9jaygp CisgICAgcHV0X3BhZ2UoKQorCiBwYWdlX21heWJlX2RtYV9waW5uZWQoKTogdGhlIHdob2xlIHBv aW50IG9mIHBpbm5pbmcKID09PT09PT09PT09PT09PT09PT09PT09PT09PT09PT09PT09PT09PT09 PT09PT09PT09PQogCi0tIAoyLjI2LjIKCl9fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19f X19fX19fX19fX19fX19fClZpcnR1YWxpemF0aW9uIG1haWxpbmcgbGlzdApWaXJ0dWFsaXphdGlv bkBsaXN0cy5saW51eC1mb3VuZGF0aW9uLm9yZwpodHRwczovL2xpc3RzLmxpbnV4Zm91bmRhdGlv bi5vcmcvbWFpbG1hbi9saXN0aW5mby92aXJ0dWFsaXphdGlvbg==