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=-6.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 A8922C47254 for ; Tue, 5 May 2020 20:29:04 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 5A39C24971 for ; Tue, 5 May 2020 20:29:04 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="CejyCH2+" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5A39C24971 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 08EE38E0006; Tue, 5 May 2020 16:29:04 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 018168E0003; Tue, 5 May 2020 16:29:03 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E48EA8E0006; Tue, 5 May 2020 16:29:03 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0203.hostedemail.com [216.40.44.203]) by kanga.kvack.org (Postfix) with ESMTP id C8D5C8E0003 for ; Tue, 5 May 2020 16:29:03 -0400 (EDT) Received: from smtpin29.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 7FC861697E for ; Tue, 5 May 2020 20:29:03 +0000 (UTC) X-FDA: 76783804566.29.store23_4f0a3cbde1e10 X-HE-Tag: store23_4f0a3cbde1e10 X-Filterd-Recvd-Size: 10508 Received: from mail-lf1-f67.google.com (mail-lf1-f67.google.com [209.85.167.67]) by imf01.hostedemail.com (Postfix) with ESMTP for ; Tue, 5 May 2020 20:29:03 +0000 (UTC) Received: by mail-lf1-f67.google.com with SMTP id x73so116122lfa.2 for ; Tue, 05 May 2020 13:29:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=83UCtPNkqDZBKGoRIazdaAZRxxGX8f38Okq8k7GA4pI=; b=CejyCH2+i8WjwOb6iQSU/zjkgAjhZFS3kKbmAcGRM+1VtTGKGEU+WvbOY7x2voOPho XLjfmulIDc05d7z63UFfBbfOwjtdaXNdU6aYilayzlrXcoKs2Scd/9SK20k+tLtbbMp6 n9nDQ3nkLOzgi5LtpjnS/IKdbwlyQQCsDCcNqYlzoRBaW4vZvEOnLbQUXDzHAGqefQGe Q1AP1nacbWbmjUwWFXOiAHyZXwLAXI/sGF3FtUqGf+6nDIg6RIe8xlpo4X2jbPbPgjId 2m0DslzgGLGYJfe8SAGJ267eW+mbvJ4JEiIJQt7G2m+lSjdotbOCUzSYiGG6gAD7sGlY 1jBQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=83UCtPNkqDZBKGoRIazdaAZRxxGX8f38Okq8k7GA4pI=; b=PFEWZ1o6G+No30ecpRqbKPuQtlGXAn31U+1a5kDMuCU2enfcj0gts/AVTOQpaEyeVU WQ5kRxrHabacpZQ1/kkRLFimjOstG2QP6TwwnMIKPDJbmWoV0xDcwC/HTvD/Mon437Ba 7HWDOzEmfG1BNpzqx1oR4i3WYjRQH4vAL3h6CtZozaUiFmupzzI0IODO1jLDe/AX7vQ9 Co6LJyGQr3XG/yh/G4HGECo7a3vVQAXnRWT6scDUbe2jzfWusvQ9qe5x5HuPHt1yPRdn 4sw5GIBZLem03VswkidB2OPc7G1SpvttIbOr0spOAXeRrn5fWmsre9Nms6ujR/Bc6rts JQWg== X-Gm-Message-State: AGi0PuZzDKkZhAPa15Z4NmvFFku7Vxh6ggLtDJ0QeiVCYPjZYH+WyEUC vvwJp6HOtHO8CdoOelH6TQcS+Sj8B4EefhXPMbA= X-Google-Smtp-Source: APiQypIN32pISCAGZuC8E0y4X/FTimjvo06gX0G57fdlSriZX05RtvQUHDYaxCoByWoKjEhFoEzhC0rF5wxgjntlPtc= X-Received: by 2002:a19:c349:: with SMTP id t70mr2736495lff.139.1588710541439; Tue, 05 May 2020 13:29:01 -0700 (PDT) MIME-Version: 1.0 References: <1588706059-4208-1-git-send-email-jrdr.linux@gmail.com> <0bfe4a8a-0d91-ef9b-066f-2ea7c68571b3@nvidia.com> In-Reply-To: <0bfe4a8a-0d91-ef9b-066f-2ea7c68571b3@nvidia.com> From: Souptick Joarder Date: Wed, 6 May 2020 02:06:56 +0530 Message-ID: Subject: Re: [RFC] mm/gup.c: Updated return value of {get|pin}_user_pages_fast() To: John Hubbard Cc: Tony Luck , fenghua.yu@intel.com, Rob Springer , Todd Poynor , benchan@chromium.org, Greg KH , Jens Wiklander , Andrew Morton , santosh.shilimkar@oracle.com, "David S. Miller" , kuba@kernel.org, Jan Kara , Ira Weiny , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , inux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org, "open list:ANDROID DRIVERS" , tee-dev@lists.linaro.org, Linux-MM , netdev@vger.kernel.org, linux-rdma@vger.kernel.org, rds-devel@oss.oracle.com Content-Type: text/plain; charset="UTF-8" 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: On Wed, May 6, 2020 at 1:08 AM John Hubbard wrote: > > On 2020-05-05 12:14, Souptick Joarder wrote: > > Currently {get|pin}_user_pages_fast() have 3 return value 0, -errno > > and no of pinned pages. The only case where these two functions will > > return 0, is for nr_pages <= 0, which doesn't find a valid use case. > > But if at all any, then a -ERRNO will be returned instead of 0, which > > means {get|pin}_user_pages_fast() will have 2 return values -errno & > > no of pinned pages. > > > > Update all the callers which deals with return value 0 accordingly. > > Hmmm, seems a little shaky. In order to do this safely, I'd recommend > first changing gup_fast/pup_fast so so that they return -EINVAL if > the caller specified nr_pages==0, and of course auditing all callers, > to ensure that this won't cause problems. While auditing it was figured out, there are 5 callers which cares for return value 0 of gup_fast/pup_fast. What problem it might cause if we change gup_fast/pup_fast to return -EINVAL and update all the callers in a single commit ? > > The gup.c documentation would also need updating in a couple of comment > blocks, above get_user_pages_remote(), and __get_user_pages(), because > those talk about a zero return value. OK. > > This might be practical without slowing down the existing code, because > there is already a check in place, so just tweaking it like this (untested) > won't change performance at all: > > diff --git a/mm/gup.c b/mm/gup.c > index 11fda538c9d9..708eed79ae29 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -2787,7 +2787,7 @@ static int internal_get_user_pages_fast(unsigned long start, > int nr_pages, > end = start + len; > > if (end <= start) > - return 0; > + return -EINVAL; > if (unlikely(!access_ok((void __user *)start, len))) > return -EFAULT; > > ...although I might be missing some other things that need a similar change, > so you should look carefully for yourself. Do you refer to other gup APIs similar to gup_fast/pup_fast ? > > > Once that change (and anything I missed) is in place, then you could go > ahead and stop handling ret==0 cases at the call sites. > > > thanks, > -- > John Hubbard > NVIDIA > > > > > Signed-off-by: Souptick Joarder > > --- > > arch/ia64/kernel/err_inject.c | 2 +- > > drivers/platform/goldfish/goldfish_pipe.c | 2 +- > > drivers/staging/gasket/gasket_page_table.c | 4 ++-- > > drivers/tee/tee_shm.c | 2 +- > > mm/gup.c | 6 +++--- > > net/rds/rdma.c | 2 +- > > 6 files changed, 9 insertions(+), 9 deletions(-) > > > > diff --git a/arch/ia64/kernel/err_inject.c b/arch/ia64/kernel/err_inject.c > > index 8b5b8e6b..fd72218 100644 > > --- a/arch/ia64/kernel/err_inject.c > > +++ b/arch/ia64/kernel/err_inject.c > > @@ -143,7 +143,7 @@ static DEVICE_ATTR(name, 0644, show_##name, store_##name) > > int ret; > > > > ret = get_user_pages_fast(virt_addr, 1, FOLL_WRITE, NULL); > > - if (ret<=0) { > > + if (ret < 0) { > > #ifdef ERR_INJ_DEBUG > > printk("Virtual address %lx is not existing.\n",virt_addr); > > #endif > > diff --git a/drivers/platform/goldfish/goldfish_pipe.c b/drivers/platform/goldfish/goldfish_pipe.c > > index 1ab207e..831449d 100644 > > --- a/drivers/platform/goldfish/goldfish_pipe.c > > +++ b/drivers/platform/goldfish/goldfish_pipe.c > > @@ -277,7 +277,7 @@ static int goldfish_pin_pages(unsigned long first_page, > > ret = pin_user_pages_fast(first_page, requested_pages, > > !is_write ? FOLL_WRITE : 0, > > pages); > > - if (ret <= 0) > > + if (ret < 0) > > return -EFAULT; > > if (ret < requested_pages) > > *iter_last_page_size = PAGE_SIZE; > > diff --git a/drivers/staging/gasket/gasket_page_table.c b/drivers/staging/gasket/gasket_page_table.c > > index f6d7157..1d08e1d 100644 > > --- a/drivers/staging/gasket/gasket_page_table.c > > +++ b/drivers/staging/gasket/gasket_page_table.c > > @@ -489,11 +489,11 @@ static int gasket_perform_mapping(struct gasket_page_table *pg_tbl, > > ret = get_user_pages_fast(page_addr - offset, 1, > > FOLL_WRITE, &page); > > > > - if (ret <= 0) { > > + if (ret < 0) { > > dev_err(pg_tbl->device, > > "get user pages failed for addr=0x%lx, offset=0x%lx [ret=%d]\n", > > page_addr, offset, ret); > > - return ret ? ret : -ENOMEM; > > + return ret; > > } > > ++pg_tbl->num_active_pages; > > > > diff --git a/drivers/tee/tee_shm.c b/drivers/tee/tee_shm.c > > index bd679b7..2706a1f 100644 > > --- a/drivers/tee/tee_shm.c > > +++ b/drivers/tee/tee_shm.c > > @@ -230,7 +230,7 @@ struct tee_shm *tee_shm_register(struct tee_context *ctx, unsigned long addr, > > if (rc > 0) > > shm->num_pages = rc; > > if (rc != num_pages) { > > - if (rc >= 0) > > + if (rc > 0) > > rc = -ENOMEM; > > ret = ERR_PTR(rc); > > goto err; > > diff --git a/mm/gup.c b/mm/gup.c > > index 50681f0..8d293ed 100644 > > --- a/mm/gup.c > > +++ b/mm/gup.c > > @@ -2760,7 +2760,7 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages, > > end = start + len; > > > > if (end <= start) > > - return 0; > > + return -EINVAL; > > if (unlikely(!access_ok((void __user *)start, len))) > > return -EFAULT; > > > > @@ -2805,8 +2805,8 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages, > > * calling get_user_pages(). > > * > > * Returns number of pages pinned. This may be fewer than the number requested. > > - * If nr_pages is 0 or negative, returns 0. If no pages were pinned, returns > > - * -errno. > > + * If nr_pages is 0 or negative, returns -errno. If no pages were pinned, > > + * returns -errno. > > */ > > int get_user_pages_fast(unsigned long start, int nr_pages, > > unsigned int gup_flags, struct page **pages) > > diff --git a/net/rds/rdma.c b/net/rds/rdma.c > > index a7ae118..44b96e6 100644 > > --- a/net/rds/rdma.c > > +++ b/net/rds/rdma.c > > @@ -161,7 +161,7 @@ static int rds_pin_pages(unsigned long user_addr, unsigned int nr_pages, > > gup_flags |= FOLL_WRITE; > > > > ret = pin_user_pages_fast(user_addr, nr_pages, gup_flags, pages); > > - if (ret >= 0 && ret < nr_pages) { > > + if (ret > 0 && ret < nr_pages) { > > unpin_user_pages(pages, ret); > > ret = -EFAULT; > > } > > >