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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D67B1C982DE for ; Mon, 21 Sep 2026 09:32:30 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id C9A3D6B00C7; Mon, 21 Sep 2026 05:32:29 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id C72306B00E1; Mon, 21 Sep 2026 05:32:29 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B877C6B00E5; Mon, 21 Sep 2026 05:32:29 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 80D236B00C7 for ; Mon, 21 Sep 2026 05:32:29 -0400 (EDT) Received: from smtpin10.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 800F01C2F94 for ; Mon, 21 Sep 2026 09:32:28 +0000 (UTC) X-FDA: 85237253976.10.E5AF4AE Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf02.hostedemail.com (Postfix) with ESMTP id BEB2C80003 for ; Mon, 21 Sep 2026 09:32:26 +0000 (UTC) Authentication-Results: imf02.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=EiR2ktE5; spf=pass (imf02.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1789983146; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=YYR5qVSNGypuoPk4MWOVXb7SNwRU6tu0qAlYq1SIKq4=; b=AUFpveSjNDBRAF84krjTijPB8QRgOPj/MsZwTQ0mDVf8uf1vSpD5hEO/vqvEqQFiPwJo2v kP7exIWbhbJfjmvwlQ/Tfv1rg3DZWMNf5MXuHkrzTcW0XAWO8vETIwhgogF23hjsMNWu2s SFiz64vADfsVDWdrMT7imiMTOhYhep8= ARC-Authentication-Results: i=1; imf02.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=EiR2ktE5; spf=pass (imf02.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1789983146; b=qETzTWuKDNVTaP8nTRIUPMGXhp0srTcULQsR+0JtrQZjblElXc831E+Mwg0wiqkQJK1tVC Dv37OEKTU1bTV2b7od0rQqx/sISaPhcqlbzP8VhDwl47wYy+8DLB/8uCL/FIjTnN9txiCM CvW2F24vLsMbXkQQNixBe1HeO3YTMgk= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 81E24600D1; Mon, 21 Sep 2026 09:32:25 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E04791F000FF; Mon, 21 Sep 2026 09:32:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789983145; bh=YYR5qVSNGypuoPk4MWOVXb7SNwRU6tu0qAlYq1SIKq4=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=EiR2ktE5bWvCWZK2xZovGpxWGGzeb+rPS5X4wbkKw1+lhJsvN+ZhauW30Gmk+VICF B6WsjoFZiPQlJm6zYFnispjSdhqDgBrA83GqOYc9yPLoKD22vhubSfV+6zO/wd8vWI K6ymAsrEO0K3o7WtIvhTWCCfxjaC3L3v1df2ifYXlUI8kAtMZgqT65Tb39EwSrmiEJ XhoNLIW67BTaDDljGDfoArCWVzZkUtAUqWXrXnvVXuHSyIburK7teC1/ioEipBlbR7 1kEp5/WaQQwSk9l1q29y72XL8jMs3WHfAYYJQWYj5+zg0viR/PHATQwjo7HtFjGTN5 8ddCwV2uNcG7g== Message-ID: <80925c1f-73c2-45df-ac26-fdcc96ffe764@kernel.org> Date: Mon, 21 Sep 2026 11:32:19 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm/gup: honour FOLL_PIN in NOMMU __get_user_pages_locked() To: Lance Yang Cc: akpm@linux-foundation.org, jgg@ziepe.ca, jhubbard@nvidia.com, gregkh@linuxfoundation.org, peterx@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260919-nommu_gup_pin-v3-1-3660a8851243@kernel.org> <20260921024914.12819-1-lance.yang@linux.dev> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20260921024914.12819-1-lance.yang@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: BEB2C80003 X-Stat-Signature: fctbxqfnajsmhzt9atpmkfa15akpkfoi X-Rspam-User: X-HE-Tag: 1789983146-922751 X-HE-Meta: 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 /sd+35qj qT5cXf2oE3K0j+Ia9cpeYQ0nMmHkvui/vCQ0XRX2cj5d3rn7KmmES6VswGh3+plThuds8ZuuZlkM5gD6hU5DHHW3+kZzU+9r4JwADLfXASgZTuznSMhlTMWq1LjBV96MAKeWc/0ZzHvbCl9hos/Rz0D4w7vU7SHZF5ywNvsTkvWKoVJqMry4iD8fTUOisCRv0oqiTtp3F+YYdYAvCvYCRVilYarrT07R5CJg/qjOfGJchQoWEn/d5zisxpo+LKqThee7m0ZE6CwaeiezIG1b5I70+licCC+6qyChfMQHWHrx8AjjcOCvT/HAtN3ZrwoZ0SlljzNoZbqU4BWrCrI8wTsnPj20FcAIhkrTrLgUUngwTnTpZwIMoo8cWoW0Qu6/k42vaANY0i5WM91HEKBxcx0IV/K4m3FRMTHzGrvdXTlxhcRtuw+idVRZb05ODFb2Pcn8KWdpvnioRik4R32BiKo0PKoDAXV53d99DoeYAW+P+qde5mPRjXj4NlNVPqfBINaj8Pn8NMgmHCZMh4lPmNWFqHxAGJOm9J9ePoTY8Z59duDI= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/21/26 04:49, Lance Yang wrote: > > On Sat, Sep 19, 2026 at 12:04:36PM +0200, David Hildenbrand (arm) wrote: >> From: Greg Kroah-Hartman >> >> The !CONFIG_MMU implementation of __get_user_pages_locked() takes a bare >> get_page() reference for each page regardless of foll_flags: >> if (pages[i]) >> get_page(pages[i]); >> >> This is reached from pin_user_pages*() with FOLL_PIN set. >> unpin_user_page() is shared between MMU and NOMMU configurations and >> unconditionally calls gup_put_folio(..., FOLL_PIN), which subtracts >> GUP_PIN_COUNTING_BIAS (1024) from the folio refcount. >> >> This means that pin adds 1, and then unpin will subtract 1024. >> >> If a user maps a page (refcount 1), registers it 1023 times as an >> io_uring fixed buffer (1023 pin_user_pages calls -> refcount 1024), then >> unregisters: the first unpin_user_page subtracts 1024, refcount hits 0, >> the page is freed and returned to the buddy allocator. The remaining >> 1022 unpins write into whatever was reallocated, and the user's VMA >> still maps the freed page (NOMMU has no MMU to invalidate it). >> Reallocating the page for an io_uring pbuf_ring then lets userspace >> corrupt the new owner's data through the stale mapping. >> >> Use try_grab_folio() which adds GUP_PIN_COUNTING_BIAS for FOLL_PIN and 1 >> for FOLL_GET, mirroring the CONFIG_MMU path so pin and unpin are >> symmetric. Keep supporting the traditional behavior where users specify >> a pages array but don't set FOLL_GET. >> >> While at it, don't return NULL pointers in the page array, >> as this is really not expected for GUP users; instead, just fail and return >> -EFAULT. >> >> [ david: support traditional behavior with no FOLL_GET, extend >> description ] >> >> Cc: Andrew Morton >> Cc: David Hildenbrand >> Cc: Jason Gunthorpe >> Cc: John Hubbard >> Cc: Peter Xu >> Reported-by: Anthropic >> Fixes: 3faa52c03f44 ("mm/gup: track FOLL_PIN pages") >> Assisted-by: gkh_clanker_t1000 >> Signed-off-by: Greg Kroah-Hartman >> Signed-off-by: David Hildenbrand (Arm) >> --- >> I added a best-guess fixes tag. Given that this has been around for a >> while ... and it's nommu, I think this is fine just going into the next >> merge window. In that case, I will pick this up myself. If we want this >> as a hotfix, Andrew please pick it up. >> --- >> mm/gup.c | 17 ++++++++++++++--- >> 1 file changed, 14 insertions(+), 3 deletions(-) >> >> diff --git a/mm/gup.c b/mm/gup.c >> index eb898ea1ee22e..1681bea8eed7e 100644 >> --- a/mm/gup.c >> +++ b/mm/gup.c >> @@ -1659,6 +1659,10 @@ static __always_inline long __get_user_pages_locked(struct mm_struct *mm, >> if (!nr_pages) >> return 0; >> >> + /* See the MMU variant: support the traditional behavior. */ >> + if (pages && !(flags & FOLL_PIN)) >> + flags |= FOLL_GET; >> + > > Wait ... isn't this the wrong __get_user_pages_locked()? The MMU version > already does this a few lines below ... > Yes, Sashiko complained as well. Will fix it up and send a v2. Lesson learned: don't work on nommu patches on Saturday ;) > Shouldn't the NOMMU version get the check instead, using foll_flags? Yes, I'll fix that up and send a v2. -- Cheers, David