From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 C118D379C40 for ; Mon, 1 Jun 2026 15:56:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780329413; cv=none; b=J6JoQa9vc5g8UxdO2JrX+ivifp8jOyEGvXLxyvbaY3EFsVFIeqwyrZ17RaSTewQsGYhy8BZlgrwjv46zSDM6E3kl6w7dFnTejCC22faTLOTsz+fAhTTsgJXfnb9ocEeeK3Kt6bDzao8E0TT2JDyyMIlZZc6bJ/CFfAFuRp2sJuw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780329413; c=relaxed/simple; bh=W3eCFDB4azfC1Z0Q1uCqB8ytT6F1GmpGp1ypDrhEddY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=jXKDce23vXED8hm86Qsk+FA1MlOeldd+lWHtoizvpD6vqza/3AAEpgRlU5BG6ZFWXXAZwPVLb1EYQ0onpBJq1XBqTEzRZ67Hc8EwekGxeZQ3iopdIczCqNNuwHMIEKuOQnp6EbQG3SXs5Ov+1Ii80oJ7DDrApHemjFJypqpzPx4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=hpgHRa1v; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="hpgHRa1v" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4A3CD1F00893; Mon, 1 Jun 2026 15:56:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780329412; bh=h1LOXYWGnyE1v0dMMQCjT19PvBVTyDuJ+KlM/Hm4iR8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=hpgHRa1vdTJkWwT53uYam3CM0oNfWlHdzxlGJiI4qYqBdKPPuOaRLEUfGZ57PnXHN 9PKoN2fb+ekqhbaI9oiQl4HBbih19TTPDbCNiq+UUJJM+/cwBLxK+/ByQoIQlO73xp ChdLzkayLF8TbUB0iMcW6xEng1d3jue6RXYGrCbeSydcwgEK7jrXLR6Pultn49OQZT Lhi3J2CDGTuNFJXWXaLE+Fm6M/gpiND627FOuZl8RRN+nxNaHR9ngQN+cB37oJWfmZ tHm8r0ulMtgjCXMyFGrcNNcsFCAMC+VNIPP7VamB5Sien1dIiT8Rx9tFuUv7p5tx9O 3M59R/QJZtb+Q== Message-ID: Date: Mon, 1 Jun 2026 17:56:45 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-hotfixes] mm/huge_memory: use correct flags for device private PMD entry To: Dev Jain , Lorenzo Stoakes , Andrew Morton Cc: Zi Yan , Baolin Wang , "Liam R . Howlett" , Nico Pache , Ryan Roberts , Barry Song , Lance Yang , SeongJae Park , Balbir Singh , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Wei Yang References: <20260601083044.57132-1-ljs@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 6/1/26 17:50, Dev Jain wrote: > > > On 01/06/26 2:00 pm, Lorenzo Stoakes wrote: >> Commit 65edfda6f3f2 ("mm/rmap: extend rmap and migration support >> device-private entries") updated set_pmd_migration_entry() to use >> pmdp_huge_get_and_clear() in the softleaf case, but made no further >> adjustments to the function itself. >> >> Therefore this function continues to incorrectly use pmd_write(), >> pmd_soft_dirty() and pmd_uffd_wp() to determine whether the installed >> migration entry should be marked writable, softdirty or uffd-wp >> respectively. >> >> Whilst all are incorrect, the most problematic of these is pmd_write(), as >> this can lead to corrupted rmap state. >> >> On x86-64 _PAGE_SWP_SOFT_DIRTY is aliased to _PAGE_RW. So calling >> pmd_write() on a softleaf will return the softdirty state encoded in the >> entry, assuming CONFIG_MEM_SOFT_DIRTY was enabled. >> >> This was observed when running the hmm.hmm_device_private.anon_write_child >> selftest: >> >> 1. The test faults in a range then migrates it such that a device-private >> THP range is established. >> >> 2. The parent then migrates it to a device-private writable PMD entry whose >> folio is entirely AnonExclusive with entire_mapcount=1, softdirty set >> (accidentally correct write state). >> >> 3. The parent forks and the PMD entries are set to device-private read only >> entries, entire_mapcount=2, softdirty still set. >> >> 4. [BUG] The child writes to the range then migrates to RAM - intending to >> install non-writable migration entries - but replacing parent and child >> PMD mappings with WRITABLE entries due to misinterpreting the softdirty >> bit. >> >> 5. In remove_migration_pmd(), if !softleaf_is_migration_read(entry) we >> set the RMAP_EXCLUSIVE flag when calling folio_add_anon_rmap_pmd() for >> both parent and child, which are therefore AnonExclusive. >> >> 6. [SPLAT] Child sets migrated folio entire_mapcount=1, parent sets >> entire_mapcount=2 and we end up with an AnonExclusive folio with >> entire_mapcount=2! Assert fires in __folio_add_anon_rmap(): >> >> VM_WARN_ON_FOLIO(folio_test_large(folio) && >> folio_entire_mapcount(folio) > 1 && >> PageAnonExclusive(cur_page), folio) >> >> This patch fixes the issue by correctly referencing the softleaf entry >> fields for writable, softdirty and uffd-wp in set_pmd_migration_entry(). >> >> It also only updates A/D flags if the entry is present as these are >> otherwise not meaningful for a softleaf entry. >> >> This patch also flips the if (!present) { ... } else { ... } logic in >> set_pmd_migration_entry() so it is easier to understand, and adds some >> comments to make things clearer. >> >> I was able to bisect this to commit 775465fd26a3 ("lib/test_hmm: add zone >> device private THP test infrastructure") which first exposes this bug as it >> was the commit that permitted test_hmm to generate the test. >> >> However commit 65edfda6f3f2 ("mm/rmap: extend rmap and migration support >> device-private entries") is the commit that actually enabled this >> behaviour. >> >> Fixes: 65edfda6f3f2 ("mm/rmap: extend rmap and migration support device-private entries") >> Cc: stable@vger.kernel.org >> Signed-off-by: Lorenzo Stoakes >> --- > > Sashiko continues to find existing problems :) What do you think: > > https://sashiko.dev/#/patchset/20260601083044.57132-1-ljs%40kernel.org IIRC, Wei is already working on fixing what it reports here regarding try_to_migrate_one(). So it's old news. https://lore.kernel.org/r/20260508013728.21285-1-richard.weiyang@gmail.com -- Cheers, David