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 30F141062870 for ; Wed, 11 Mar 2026 11:59:54 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 413BA6B0005; Wed, 11 Mar 2026 07:59:53 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 397176B0089; Wed, 11 Mar 2026 07:59:53 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 27A396B008A; Wed, 11 Mar 2026 07:59:53 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 024916B0005 for ; Wed, 11 Mar 2026 07:59:52 -0400 (EDT) Received: from smtpin04.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 860F11BC7F for ; Wed, 11 Mar 2026 11:59:52 +0000 (UTC) X-FDA: 84533638224.04.1182617 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf14.hostedemail.com (Postfix) with ESMTP id CDD0E10000E for ; Wed, 11 Mar 2026 11:59:50 +0000 (UTC) Authentication-Results: imf14.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=MccQFE2M; spf=pass (imf14.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=1773230390; 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=avFdgyEmxp+APIC/ua1v84vQo5qGvtsR9s+DnHlViA8=; b=FiVzJBhl66ycBSHNFUbc5RvA44Qtr9mH/qlnA0SJTTF7UN3LgjhLFVTSI7ocQWwqv4x20C 9YeZ3AseWDCcTQcbMLzmsOGFCEPX0Cst8ArmXwG/M2iAehHCEccBfRGffqPPnGSsxIK9dC MBcpoO/0VRJi2bmnYOKenEqcF8cOCqo= ARC-Authentication-Results: i=1; imf14.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=MccQFE2M; spf=pass (imf14.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; s=arc-20220608; d=hostedemail.com; t=1773230390; a=rsa-sha256; cv=none; b=zLxgo2pQxIU+7PyaThQE1JqHPuKtmYfQ/b35fEtNhnSppFlhZBmw9lu+fzGYcvTu9t7Oym yRB8SkYTVkyAZWAFGXZJhtyHAApQFv8jrcJFNPZ/jKcvLY6X8OrBDykhIxhFADdcB6eo3D ILKkmFDdYYBJ5ryxwDX+6scasragVLQ= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 24A3260145; Wed, 11 Mar 2026 11:59:50 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id DC756C4CEF7; Wed, 11 Mar 2026 11:59:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773230389; bh=7L05EWimhuh0T0G4AbugcywDE/W3b5BIQqPB/jlupZU=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=MccQFE2MB47oXOOb4mvYNYBpxTNQR8cze+E2vn7aD2JdRxlDSq3tnJm4uKmDlR4T6 5jPIeiV1/VylKk2qCrMJGpOH37F69pZS2Hwl2Zn1K84UC89TmwfLM9H6Ksqhp1g3Op 805z8YgcDJknSteio4hG1NxOzCW3e4iXA6dDdiICRLOdDbew+9c5Il2eLEiX5foq3Z hAuGezC4BWpfzlMpKOanpQtGKiIuNo9l3zIIJ0dojxN0Vhb0sOU6BZ2k6eHqzjb2Dj xCu389Z1OELcl9epnnGEcoewycabonntx2VEiuSjazqeuOeFd52N4zQ/aNTHIdg0Qg QyH+HM8rnE3cw== Message-ID: <6624bc37-8a2a-4718-bd03-32382dd28d67@kernel.org> Date: Wed, 11 Mar 2026 12:59:45 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC 1/1] mm/pagewalk: don't split device-backed huge pfnmaps To: "Boone, Max" Cc: Alex Williamson , Andrew Morton , Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , "linux-mm@kvack.org" , "kvm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "Tottenham, Max" , "Hunt, Joshua" , "Pelland, Matt" References: <20260309174949.2514565-1-mboone@akamai.com> <20260309174949.2514565-2-mboone@akamai.com> <51eeb09d-d3f4-412f-85da-690fdc0f8e6a@kernel.org> <83842620-AD01-4619-845F-8DE7DF1F8F31@akamai.com> <0a652e7e-339e-4f98-b591-7fe5680e2006@kernel.org> <6CBB0401-26DD-4EF9-949C-54BEAD3ABA33@akamai.com> <5fb9beef-b6fe-401a-aa24-aade48b795d4@kernel.org> <0A734214-9E4B-4A65-AFB1-055883639358@akamai.com> <928CF80F-7436-42ED-9791-F63E3D699CBE@akamai.com> 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: <928CF80F-7436-42ED-9791-F63E3D699CBE@akamai.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: CDD0E10000E X-Rspamd-Server: rspam07 X-Stat-Signature: 3nweneqqurdpws5j113kueinu4h3pcir X-Rspam-User: X-HE-Tag: 1773230390-295073 X-HE-Meta: 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 NllVB+EY G4Mbc0WmOPy0mzkVSKHgkZDJI801l9vPPSLucVrSNs/ec2zeHKJ6cwQCCwZ23htZxF1cNJBHf/nXfQBPt/qTKzLhWgGTc7QLgLjO2A2SUApVuCXqQnv6kr4bbnb/jnQ1hhdnkMQPemWsHnZkfcOaXoJnGmcMD04ZUEZ2tPGF25Pc/3mojHN0kMKZYftbSlowlik+ZZ0BWq1ggLtrF1VQlZtqUnqR84FMH0Jv/iZKWQFvmogxVJg4vlUX0SIUzfJuT3etZvIxNmgAzlRRYlS3I02W4J4cyN92gaZaDNrnVv8vD+9C1nuw+fso4hQZTbsXHS6+W7vknssTexLyYjwVqacCzRWHUCxQtGUVq Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/11/26 12:14, Boone, Max wrote: > > >> On Mar 11, 2026, at 11:45 AM, David Hildenbrand (Arm) wrote: >> >> The code in follow_fault_pfn() should likely be updated to handle more >> than one attempt. That's also what GUP does. >> >> Likely, follow_fault_pfn() was never taught about PFNMAP mappings that >> can be faulted+zapped (in the past they were always static). >> >> If you turn that into a (possibly) endless loop, does the problem go away? > > Yep, was just trying that - with this change the problem goes away: > > --- a/drivers/vfio/vfio_iommu_type1.c > +++ b/drivers/vfio/vfio_iommu_type1.c > @@ -532,7 +532,7 @@ static int follow_fault_pfn(struct vm_area_struct *vma, struct mm_struct *mm, > > ret = follow_pfnmap_start(&args); > if (ret) > - return ret; > + return -EAGAIN; > } Looks like follow_pfnmap_start() only ever returns -EINVAL: for invalid parameters (unexpected) and non-present entries. Returning -ENOENT when there is no actual entry would be clearer. Then you could just translate -ENOENT to -EAGAIN. But just always using -EAGAIN should be fine here I guess. > > if (write_fault && !args.writable) > > — > > I’ll propose that with the VFIO folks when I get the patch for mm/pagewalk.c ready and will refer > to that patch, or would it be better to propose two commits under the same cover letter? Probably be best to send two separate patches. One MM fix and one vfio fix. :) > > I can have a look at follow_fault_pfn but this problem is my first time diving into linux mm > so that will probably take a while (and some reading up on my end). No worries, just let me know if you have any questions. -- Cheers, David