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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2480BC6FD1C for ; Wed, 22 Mar 2023 10:32:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230226AbjCVKcz (ORCPT ); Wed, 22 Mar 2023 06:32:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43874 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229671AbjCVKcx (ORCPT ); Wed, 22 Mar 2023 06:32:53 -0400 Received: from mail-wr1-x430.google.com (mail-wr1-x430.google.com [IPv6:2a00:1450:4864:20::430]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 524804A1D5; Wed, 22 Mar 2023 03:32:51 -0700 (PDT) Received: by mail-wr1-x430.google.com with SMTP id m2so16473048wrh.6; Wed, 22 Mar 2023 03:32:51 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; t=1679481170; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=a1CeLNOWnRlqe1bR3xMhj6/4uAXJ9YfiUxVG0ziEESs=; b=M5p9FntqrNraUn/1fryCXq6NzFVy+lQsgH7lt2dwu/DakfDB+h8t3YtR/D9zADE97D mwTEhubIVJBVEXK4mjYpYPFbKGliQt9/jjJX4ODWOVLVbcD7rl6opRH2GIbQ+9Ir31go ynnd5v6PdiHrFQSFE04Z5fEwmhDNZCmX+ybnjW69kHzU1wBjQc/NIG4MoDkNUxM3hQ5P iq40Tjochukfgt/Sp1MMhvquA7l9G/tfwrrvGg1MfSChQE/gUy79uzfedJdRqH9VH8Lq Wq4lEHKUy+GyM6DYvW+J5jOvVseJFAgy6gQtHkaW8OMkGJrGzpi8yuD8kyiao6ld3g52 tVCQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1679481170; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=a1CeLNOWnRlqe1bR3xMhj6/4uAXJ9YfiUxVG0ziEESs=; b=eYfmtfCGdrbAvfHs52Jk44QYnmAeGRISrPnkVTjtQdzXwtXSIyjTTXwY/nm3PmJOu5 6+3ZUb0T9mEx2QXIS0Qx3UrzpN20A3BTFUvLWbox5k+IlRGT+NMglIrwD+SiLo7cOxJb syEbeJgxbfvID3pZScAuWhXCmenYnKxoS7CvvL+IedJvq26mlV/snK3T6PF1nXjo37Kk rBwiida+BixqDaQP1WKbh3v5EMG9Vs3fSv3e0QJcgMt+DaGVhBDbSvijdBbtzmFsn0Za kaPwC9EOdmQV5wabMrOTIjp0oZUsF1kMIPgRs1mDM1Q8P8TnV5P7LB3wL3StQSbxKDDm zkoA== X-Gm-Message-State: AO0yUKV9OwppT0LaEQu7iY1sxFTvAs1N0KDzzrmBBx6EK80IsoROj69B NXIODM/XN6uZeuet/TubgZc= X-Google-Smtp-Source: AK7set/53fxO++ICPo9CDCI6k2GRYpLxmnmZZ+pCn6q2L+UDEhM2Lva/0vi7LOq/h8NTmOccPbVvfw== X-Received: by 2002:a5d:6245:0:b0:2c5:4ca3:d56c with SMTP id m5-20020a5d6245000000b002c54ca3d56cmr1406977wrv.0.1679481169582; Wed, 22 Mar 2023 03:32:49 -0700 (PDT) Received: from localhost ([2a00:23c5:dc8c:8701:1663:9a35:5a7b:1d76]) by smtp.gmail.com with ESMTPSA id h5-20020a5d4305000000b002c3f81c51b6sm13440307wrq.90.2023.03.22.03.32.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Mar 2023 03:32:48 -0700 (PDT) Date: Wed, 22 Mar 2023 10:32:47 +0000 From: Lorenzo Stoakes To: Baoquan He Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Andrew Morton , Uladzislau Rezki , Matthew Wilcox , David Hildenbrand , Liu Shixin , Jiri Olsa , Jens Axboe , Alexander Viro Subject: Re: [PATCH v4 3/4] iov_iter: add copy_page_to_iter_atomic() Message-ID: References: <31482908634cbb68adafedb65f0b21888c194a1b.1679431886.git.lstoakes@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 22, 2023 at 06:17:25PM +0800, Baoquan He wrote: > On 03/21/23 at 08:54pm, Lorenzo Stoakes wrote: > > Provide an atomic context equivalent for copy_page_to_iter(). This eschews > > the might_fault() check copies memory in the same way that > > copy_page_from_iter_atomic() does. > > > > This functions assumes a non-compound page, however this mimics the > > existing behaviour of copy_page_from_iter_atomic(). I am keeping the > > behaviour consistent between the two, deferring any such change to an > > explicit folio-fication effort. > > > > This is being added in order that an iteratable form of vread() can be > > implemented with known prefaulted pages to avoid the need for mutex > > locking. > > > > Signed-off-by: Lorenzo Stoakes > > --- > > include/linux/uio.h | 2 ++ > > lib/iov_iter.c | 28 ++++++++++++++++++++++++++++ > > 2 files changed, 30 insertions(+) > > > > diff --git a/include/linux/uio.h b/include/linux/uio.h > > index 27e3fd942960..fab07103090f 100644 > > --- a/include/linux/uio.h > > +++ b/include/linux/uio.h > > @@ -154,6 +154,8 @@ static inline struct iovec iov_iter_iovec(const struct iov_iter *iter) > > > > size_t copy_page_from_iter_atomic(struct page *page, unsigned offset, > > size_t bytes, struct iov_iter *i); > > +size_t copy_page_to_iter_atomic(struct page *page, unsigned offset, > > + size_t bytes, struct iov_iter *i); > > 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); > > diff --git a/lib/iov_iter.c b/lib/iov_iter.c > > index 274014e4eafe..48ca1c5dfc04 100644 > > --- a/lib/iov_iter.c > > +++ b/lib/iov_iter.c > > @@ -821,6 +821,34 @@ size_t copy_page_from_iter_atomic(struct page *page, unsigned offset, size_t byt > > } > > EXPORT_SYMBOL(copy_page_from_iter_atomic); > > > > +size_t copy_page_to_iter_atomic(struct page *page, unsigned offset, size_t bytes, > > + struct iov_iter *i) > > +{ > > + char *kaddr = kmap_local_page(page); > > I am a little confused about the name of this new function. In its > conterpart, copy_page_from_iter_atomic(), kmap_atomic()/kunmpa_atomic() > are used. With them, if CONFIG_HIGHMEM=n, it's like below: The reason for this is that:- 1. kmap_atomic() explicitly states that it is now deprecated and must no longer be used, and kmap_local_page() should be used instead:- * kmap_atomic - Atomically map a page for temporary usage - Deprecated! * Do not use in new code. Use kmap_local_page() instead. 2. kmap_local_page() explicitly states that it can be used in any context:- * Can be invoked from any context, including interrupts. I wanted follow this advice as strictly as I could, hence the change. However, we do need preemption/pagefaults explicitly disabled in this context (we are happy to fail if the faulted in pages are unmapped in meantime), and I didn't check the internals to make sure. So I think for safety it is better to use k[un]map_atomic() here, I'll respin and put that back in, good catch! > > static inline void *kmap_atomic(struct page *page) > { > if (IS_ENABLED(CONFIG_PREEMPT_RT)) > migrate_disable(); > else > preempt_disable(); > pagefault_disable(); > return page_address(page); > } > > But kmap_local_page() is only having page_address(), the code block > between kmap_local_page() and kunmap_local() is also atomic, it's a > little messy in my mind. > > static inline void *kmap_local_page(struct page *page) > { > return page_address(page); > } > > > + char *p = kaddr + offset; > > + size_t copied = 0; > > + > > + if (!page_copy_sane(page, offset, bytes) || > > + WARN_ON_ONCE(i->data_source)) > > + goto out; > > + > > + if (unlikely(iov_iter_is_pipe(i))) { > > + copied = copy_page_to_iter_pipe(page, offset, bytes, i); > > + goto out; > > + } > > + > > + iterate_and_advance(i, bytes, base, len, off, > > + copyout(base, p + off, len), > > + memcpy(base, p + off, len) > > + ) > > + copied = bytes; > > + > > +out: > > + kunmap_local(kaddr); > > + return copied; > > +} > > +EXPORT_SYMBOL(copy_page_to_iter_atomic); > > + > > static void pipe_advance(struct iov_iter *i, size_t size) > > { > > struct pipe_inode_info *pipe = i->pipe; > > -- > > 2.39.2 > > >