From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793221628; b=D7dOFl/l5RhP9XsDNXo+ErqvX4I/mg5sQRdppC66HAsM/YvYFkie8TXCbw3pzvA3bsoS 2zddtITu2WpXO6s7qm/pLD8bHmS0FpBuIMTiLYWjKMABsw5hleUS5HCRJccJeohrfuKEG cL4ty5d/DsEIaHsD/c/Rfx8LGtlt6D6OKye7ecalp25WWVN9ePubjl/9wy88mmhl3uWw6 mKuksK9kK3YlItLsKvwSCSKm+bePGSzZ9leRFPo3BUT6iewTLNbkUHKUYYMvUR5Nmsnnp wo29TOf8jySbutEHWujJVTyoC+OZEGwYyrq83iMl3SutYNU7LGI/uTsz9GS0+AeEIhQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793221628; h=Received:DKIM-Signature:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:From:Content-Language:Autocrypt:In-Reply-To: Content-Type:Content-Transfer-Encoding; bh=xxZoPiTulvdMTGEYFvoIZ44CCQijO9eunuLg0kQXxFk=; b=WAp++ILAbWJcRAcA7+lKgzLN/CAw47qhHh/E4bdS64UG5FOBS2608RjTj/15iE1ipAOT 10uQQaz55XD4LdS3ure11IG03/Tr5zm41Jc8FTfOq0UKmGzwch/hZoOFAmrPApVfzVMYq DBQhHuIq9qwc8sTQYPfPpwQ36XKUW8G8/EW5sK0NIvM94fg1hT6nr+kZQYXnvLmiupPps S6dO3sC3VtczuMuJCjlbG96K/xsR56o+F2iYY3rWhAM+W5fK/eTHl4YHmp5RJfHtHVDHY I0Ty2Ki6X3pAHCOD3ZBC9iZgNy4kZzch3BZ4/p6L8r7Ph6NAvpsM9cfrC9oxWxV7bXw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b="LN/bo96W"; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 01340606A31C; Wed, 28 Oct 2026 21:07:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=LN/bo96W Received: by smtp.kernel.org (Postfix) with ESMTPSA id C600A1F01825; Wed, 28 Oct 2026 21:06:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793221627; bh=xxZoPiTulvdMTGEYFvoIZ44CCQijO9eunuLg0kQXxFk=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=LN/bo96WZvsiQi1qe+JR9nlcD/dtIGQ3FMfkNtmijuD8fjEQvKUZbveUSkvBFTpiT q6Edde755VLLwfbtDICVm/OW4Pm+/etk4qBGkfzt7OHtDuZ3eCdxBEwg9OirXuns+M XsvYfyUNxV7GxmUXhpEDJCqSSig5E7leSPceajxOCaywHlCdhCxFMwskHRcKuUXv06 PDthkCr7ALLRll2jP+OhkIKbt46NDpsV5HResmFBVneLOSa8AjHiykgI/EVkjCB6+y im/ok434xapBK6Jzyew5LWXpxM6m7VRgE7Je11/Pjst7rZUdUqcoFHcm6G7+s6AIdF R9o+fP1ANqrsg== Message-ID: Date: Wed, 28 Oct 2026 22:06:49 +0100 X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 31/46] mm/mremap: fix moving PUD leaves To: Pedro Falcato Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kees Cook , Peter Zijlstra , Jann Horn , Hugh Dickins , Pasha Tatashin , Pratyush Yadav , "Matthew Wilcox (Oracle)" , Jan Kara , Zi Yan , Lance Yang , Rik van Riel , Harry Yoo , Alistair Popple , Nico Pache , Ryan Roberts , Dev Jain , Usama Arif , Kiryl Shutsemau , Matthew Brost , John Hubbard , Peter Xu , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Oscar Salvador , Minchan Kim , Muchun Song , Xu Xin , Chengming Zhou , Chris Li , Kemeng Shi , Nhat Pham , Youngjun Park , Gregory Price , Joshua Hahn , Rakie Kim , Ying Huang , Jason Gunthorpe , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, Josef Bacik , stable@vger.kernel.org References: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> <20261027-fixes_core-v1-31-6f74bec9a5bb@kernel.org> 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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/28/26 14:20, Pedro Falcato wrote: > On Tue, Oct 27, 2026 at 12:17:51AM +0100, David Hildenbrand (Arm) wrote: >> From: Josef Bacik >> >> pud_none_or_clear_bad() only really works on page tables. PUD leaves >> confuse the check and make us clear the page table entry and print a >> warning. >> >> Since commit aed877c2b4257 ("device/dax: properly refcount device dax pages >> when mapping"), this also leaks device-DAX folio references, mapcounts >> and RSS accounting, resulting in "Bad rss-counter state" warnings on exit. >> >> Allow PUD leaves in get_old_pud(). If a PUD leaf cannot be moved as a >> whole or the move fails, split it. This unmaps it with proper accounting >> instead of treating the leaf entry as a PMD table. >> >> Keep using pud_trans_huge() for now, in the future this code should be >> cleaned up to just check for PUD leaves. >> >> Fix generated by an LLM and sent by Josef Bacik in private. >> >> Fixes: a00cc7d9dd93 ("mm, x86: add support for PUD-sized transparent hugepages") >> Cc: stable@vger.kernel.org >> Signed-off-by: Josef Bacik >> Reviewed-by: Lorenzo Stoakes (ARM) >> [ david: fallthrough after splitting ] >> Signed-off-by: David Hildenbrand (Arm) > > Reviewed-by: Pedro Falcato Thanks! > >> --- >> mm/mremap.c | 9 ++++----- >> 1 file changed, 4 insertions(+), 5 deletions(-) >> >> diff --git a/mm/mremap.c b/mm/mremap.c >> index 91f0865f6aeea..1237718848f5c 100644 >> --- a/mm/mremap.c >> +++ b/mm/mremap.c >> @@ -87,7 +87,7 @@ static pud_t *get_old_pud(struct mm_struct *mm, unsigned long addr) >> return NULL; >> >> pud = pud_offset(p4d, addr); >> - if (pud_none_or_clear_bad(pud)) >> + if (!pud_trans_huge(*pud) && pud_none_or_clear_bad(pud)) >> return NULL; >> >> return pud; >> @@ -847,11 +847,10 @@ unsigned long move_page_tables(struct pagetable_move_control *pmc) >> if (!new_pud) >> break; >> if (pud_trans_huge(*old_pud)) { >> - if (extent == HPAGE_PUD_SIZE) { >> - move_pgt_entry(pmc, HPAGE_PUD, old_pud, new_pud); >> - /* We ignore and continue on error? */ >> + if (extent == HPAGE_PUD_SIZE && >> + move_pgt_entry(pmc, HPAGE_PUD, old_pud, new_pud)) >> continue; >> - } >> + split_huge_pud(pmc->old, old_pud, pmc->old_addr); > > Note that, if the HPAGE_PUD move fails, we split but miss the opportunity to > move at the PUD level (right below). Is this on purpose? Am I missing > something? I was mirroring the PMD code, really. There, we also don't seem to move a PTE page table when moving the PMD leaf failed and we split. I think part of the puzzle is: move_huge_pmd() / move_huge_pud() only really fail if there was some race with concurrent splitting. So it doesn't really happen all that often I guess. > > ... I say, realizing I am missing something, because split_huge_pmd (and > consequently split_huge_pud) just decide to zap if the VMA isn't anonymous, > and split_huge_pud() just hardcoded it to "of course it's not anonymous, lol", > and just zaps. So there's no point in moving what isn't there. Right, we don't support anonymous PUDs and file PUDs/PMDs are split by effectively zapping them (no PTE page table prealloc required). Can I hear that you are interested in cleaning up this code? :) -- Cheers, David