From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from shelob.surriel.com (shelob.surriel.com [96.67.55.147]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 95F0110F1 for ; Sat, 29 Aug 2026 02:11:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=96.67.55.147 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787969476; cv=none; b=lj0iQGfk9UxQm3Fij4kLZkGHigIDytv2kQducn6mbJX0L44ny3CAa7aQPPjuJ0jVXkEF5fzebnYQJn3JbTdpyQ8fqq5FXtTXphEZU5oFUmCBTi5RGSbYX+VA+0q1bwkMNqVFj8LRG+SQmMYt6GgmwsZudKA1e4u6YALbE3Oq90E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787969476; c=relaxed/simple; bh=4m7Aj7MKnysLygN8jaeO6jA5O3Nx7oGEa8ywJ1zsCEo=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=WnANIgo/UIfihTDuZUApW+KGh7VLfmuMCSvqotHuniSltxJGj7RnDO1UjfHlCSafiyM8hINZZMY+Vy+5DWEj5vv6/g8oPNaglofOaEJ+by/CEyN+xVDCkyJI03PeCZY232ZZRefvWrKTs8PwaJRyhfHm1p69N5lH1zRY/jdS0OI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=surriel.com; spf=pass smtp.mailfrom=surriel.com; dkim=pass (2048-bit key) header.d=surriel.com header.i=@surriel.com header.b=Ln+WBa5/; arc=none smtp.client-ip=96.67.55.147 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=surriel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=surriel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=surriel.com header.i=@surriel.com header.b="Ln+WBa5/" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=surriel.com ; s=mail; h=MIME-Version:Content-Transfer-Encoding:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID; bh=4m7Aj7MKnysLygN8jaeO6jA5O3Nx7oGEa8ywJ1zsCEo=; b=Ln+WBa 5/G2COsBtXJF9hqXRknoFtSR7DzeCepjI15pNgy+JikmwXDbPzQiWPJABunIEVxC419xO5lXwIi5F m1Flna3ngJvaRHeOklW7XRX1NmrW702Em0BBnDL6zVce1FNCl8Mi/BqXdAYT39c8a9wAX7HbcJEUV WQj9+ZipzkdsSumIydqMkFm+2fwVwHHjrJbWSsSwY3eofJsJ7kYPB2pYpXm1/XYz5BJ1jhG6lhn5a FJYnqWIGVRiAkva2JhclfsPXZdjKGn2Ak/wQnJDD3xp5ZEdtXukHyUbtNYs1kTOAdC5qWcXDIQAhu aZ3E8f9NG5b6KF9CgKmHSH8iFFRQ==; Received: from [2601:18c:8100:a0e0:5a47:caff:fe78:8708] by shelob.surriel.com with esmtpsa (TLS1.3) tls TLS_AES_256_GCM_SHA384 (Exim 4.99.5) (envelope-from ) id 1x08XD-00000009CGN-3aTV; Sat, 29 Aug 2026 02:11:07 +0000 Message-ID: <7ba9d2e6370d6134ad34cdffcff5cc79b9192df1.camel@surriel.com> Subject: Re: [RFC PATCH v3 4/8] mm/gup: break out follow_one_pte() helper From: Rik van Riel To: Suren Baghdasaryan Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, Andrew Morton , David Hildenbrand , Jason Gunthorpe , John Hubbard , Peter Xu , linux-mm@kvack.org Date: Fri, 28 Aug 2026 22:11:07 -0400 In-Reply-To: References: <20260811025157.1632867-1-riel@surriel.com> <20260811025157.1632867-5-riel@surriel.com> Autocrypt: addr=riel@surriel.com; prefer-encrypt=mutual; keydata=mQENBFIt3aUBCADCK0LicyCYyMa0E1lodCDUBf6G+6C5UXKG1jEYwQu49cc/gUBTTk33A eo2hjn4JinVaPF3zfZprnKMEGGv4dHvEOCPWiNhlz5RtqH3SKJllq2dpeMS9RqbMvDA36rlJIIo47 Z/nl6IA8MDhSqyqdnTY8z7LnQHqq16jAqwo7Ll9qALXz4yG1ZdSCmo80VPetBZZPw7WMjo+1hByv/ lvdFnLfiQ52tayuuC1r9x2qZ/SYWd2M4p/f5CLmvG9UcnkbYFsKWz8bwOBWKg1PQcaYHLx06sHGdY dIDaeVvkIfMFwAprSo5EFU+aes2VB2ZjugOTbkkW2aPSWTRsBhPHhV6dABEBAAG0HlJpayB2YW4gU mllbCA8cmllbEByZWRoYXQuY29tPokBHwQwAQIACQUCW5LcVgIdIAAKCRDOed6ShMTeg05SB/986o gEgdq4byrtaBQKFg5LWfd8e+h+QzLOg/T8mSS3dJzFXe5JBOfvYg7Bj47xXi9I5sM+I9Lu9+1XVb/ r2rGJrU1DwA09TnmyFtK76bgMF0sBEh1ECILYNQTEIemzNFwOWLZZlEhZFRJsZyX+mtEp/WQIygHV WjwuP69VJw+fPQvLOGn4j8W9QXuvhha7u1QJ7mYx4dLGHrZlHdwDsqpvWsW+3rsIqs1BBe5/Itz9o 6y9gLNtQzwmSDioV8KhF85VmYInslhv5tUtMEppfdTLyX4SUKh8ftNIVmH9mXyRCZclSoa6IMd635 Jq1Pj2/Lp64tOzSvN5Y9zaiCc5FucXtB9SaWsgdmFuIFJpZWwgPHJpZWxAc3VycmllbC5jb20+iQE +BBMBAgAoBQJSLd2lAhsjBQkSzAMABgsJCAcDAgYVCAIJCgsEFgIDAQIeAQIXgAAKCRDOed6ShMTe g4PpB/0ZivKYFt0LaB22ssWUrBoeNWCP1NY/lkq2QbPhR3agLB7ZXI97PF2z/5QD9Fuy/FD/jddPx KRTvFCtHcEzTOcFjBmf52uqgt3U40H9GM++0IM0yHusd9EzlaWsbp09vsAV2DwdqS69x9RPbvE/Ne fO5subhocH76okcF/aQiQ+oj2j6LJZGBJBVigOHg+4zyzdDgKM+jp0bvDI51KQ4XfxV593OhvkS3z 3FPx0CE7l62WhWrieHyBblqvkTYgJ6dq4bsYpqxxGJOkQ47WpEUx6onH+rImWmPJbSYGhwBzTo0Mm G1Nb1qGPG+mTrSmJjDRxrwf1zjmYqQreWVSFEt26tBpSaWsgdmFuIFJpZWwgPHJpZWxAZmIuY29tP okBPgQTAQIAKAUCW5LbiAIbIwUJEswDAAYLCQgHAwIGFQgCCQoLBBYCAwECHgECF4AACgkQznneko TE3oOUEQgAsrGxjTC1bGtZyuvyQPcXclap11Ogib6rQywGYu6/Mnkbd6hbyY3wpdyQii/cas2S44N cQj8HkGv91JLVE24/Wt0gITPCH3rLVJJDGQxprHTVDs1t1RAbsbp0XTksZPCNWDGYIBo2aHDwErhI omYQ0Xluo1WBtH/UmHgirHvclsou1Ks9jyTxiPyUKRfae7GNOFiX99+ZlB27P3t8CjtSO831Ij0Ip QrfooZ21YVlUKw0Wy6Ll8EyefyrEYSh8KTm8dQj4O7xxvdg865TLeLpho5PwDRF+/mR3qi8CdGbkE c4pYZQO8UDXUN4S+pe0aTeTqlYw8rRHWF9TnvtpcNzZw== Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.60.2 (3.60.2-1.fc44) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Fri, 2026-08-28 at 16:47 -0700, Suren Baghdasaryan wrote: > On Mon, Aug 10, 2026 at 8:07=E2=80=AFPM Rik van Riel > wrote: > >=20 > >=20 > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * We only care about a= non pages in can_follow_write_pte(). > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 */ > > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if ((flags & FOLL_WRITE) && > > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 !can_foll= ow_write_pte(pte, page, vma, flags)) { > > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0 ret =3D 0; > > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0 goto out; > > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if ((flags & FOLL_WRITE) && !can_= follow_write_pte(pte, > > page, vma, flags)) > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0 return 0; >=20 > Before refactoring in the above case we would "goto out" and > no_page_table() would not be called even if pte_none(pte). Now I > think > you will call it if pte_none(pte). I'm not sure if this does not > matter but this seems like a functional change. Good catch, now we may end up calling no_page_table() on a VMA where we are not allowed to write, for a FOLL_WRITE access, while before we did not. That might turn 0 into -EFAULT in some corner cases. I don't know if we can actually hit any of those corner cases, or whether they matter in practice, but the fix seems easy enough, so I'll fix it for v4. --=20 All Rights Reversed.