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 593574334DA for ; Wed, 22 Jul 2026 17:33:49 +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=1784741634; cv=none; b=jeGQfU27Lui0+cQqUe9nh96ds4QaNcMmV3JPdgsvSM1yuLqVYBOvSSmkBW3BG6ji/mvw7v2HT/9DpepX71sSV+Jqqt+tdM+korHatrc7pCsocukpqX0alocjFFc1qbYVPEhHoi5pQvHH1InrNpz2eTfhzPSD1d68Pgr66aogOPE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784741634; c=relaxed/simple; bh=ffF1YtoR/cZxAVUPZ8SrWZR3GBHgYP9GM5ARzRAhO38=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=XNOPkGhut2ys40QfcFpCNzM7YEKolVy/UC+XbOqZOLFUi5dOjGVQJ8cBAMCckvekNF4BDGlcm4Ax/MykCssgI4sm7V+KGtxQQLH7zaT0+qzexFEky4siK1sZmc/M6xbvEvPxSXy0pTAsWf7HhWevFrS5AiyOy7q+/fXiJjlPDdY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none 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=I2wb8lkB; arc=none smtp.client-ip=96.67.55.147 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none 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="I2wb8lkB" 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:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=ffF1YtoR/cZxAVUPZ8SrWZR3GBHgYP9GM5ARzRAhO38=; b=I2wb8lkB66vP/VbwkSxq7mxq4r aeer3+czdNVgGMs11RQYWgqHOI4/3a0jWRwchgIAgGaMP6ywwkdse2bqvB3NYD4COWIUfLWD6Cx7V 0tFfGvkiSJR6H434UcYf5LIQvyFOUwRap+XfzbEQXPKWz916j84NrF0KfY+J1zIzxG6kLAP1xdNXx 8BSYx7rVi2N1dLLqE3Qda7EsYmwpb/DqkWi4blWBh7fDzqia3m0bimO6c0Ppre+BBPDzFzkQQEWNb zH3LyltRswVnep+b2fLB074N7VdgEPDcmjqw/jLPoAIgirLPhyGrEIvdQf7+u+UMhoOhqT6Ei6JQU FoEK9ODg==; Received: from fangorn.home.surriel.com ([10.0.13.7]) by shelob.surriel.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.97.1) (envelope-from ) id 1wmap3-000000004NY-2BGF; Wed, 22 Jul 2026 13:33:33 -0400 Message-ID: <8da92b565d7ec64ea4ab2db8155a250aed0aa88b.camel@surriel.com> Subject: Re: [PATCH v3 0/6] mm: access remote process memory under the per-VMA lock From: Rik van Riel To: "David Hildenbrand (Arm)" , linux-kernel@vger.kernel.org, Andrew Morton Cc: kernel-team@meta.com, Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , linux-mm@kvack.org Date: Wed, 22 Jul 2026 13:33:33 -0400 In-Reply-To: References: <20260717170036.743149-1-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 3.56.2 (3.56.2-2.fc42) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Tue, 2026-07-21 at 20:12 +0200, David Hildenbrand (Arm) wrote: > On 7/17/26 19:00, Rik van Riel wrote: >=20 > >=20 > > get_user_pages_remote() does not fit: it hard codes the mmap lock > > and > > re-derives the VMA. get_user_page_vma() walks the page tables, > > faults a > > missing page in, and returns it with a reference and the caller's > > lock > > still held. >=20 > Agreed, and that can be tackled later. I'll stop making this series (much) bigger, then ;) I added a few things for v4, but I can save other stuff for follow-ups. >=20 > >=20 > > The per-VMA path also closes a pre-existing gap. A COWed page in a > > VM_IO/VM_PFNMAP VMA has a struct page, but the old code routed it > > to > > ->access(), where generic_access_phys() ioremaps the PFN and > > ioremap of RAM > > is rejected, so the read came up short. >=20 > Yep. The GUP code rejected VM_IO/VM_PFNMAP for, though, because it > did not > properly handle vm_normal_page_pmd() etc so far. >=20 Do we ever do a PMD sized COW on VM_IO / VM_PFNMAP VMAs? In other words, is this something we should: - leave out for now? - fix now? - fix later? If we can fix it later, I'll add it to the list. --=20 All Rights Reversed.