From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.subspace.kernel.org (Postfix) with ESMTP id CE1FF606A323 for ; Tue, 27 Oct 2026 14:42:53 +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=nCibtCOv Received: by kanga.kvack.org (Postfix) id DDC736B0793; Tue, 27 Oct 2026 10:42:52 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D8C656B0795; Tue, 27 Oct 2026 10:42:52 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C55E26B0796; Tue, 27 Oct 2026 10:42:52 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 9F0776B0793 for ; Tue, 27 Oct 2026 10:42:52 -0400 (EDT) Received: from smtpin24.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 2AE23A86B2 for ; Tue, 27 Oct 2026 14:42:52 +0000 (UTC) X-FDA: 85368672984.24.64C9374 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf08.hostedemail.com (Postfix) with ESMTP id 6B978160006 for ; Tue, 27 Oct 2026 14:42:50 +0000 (UTC) Authentication-Results: imf08.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=nCibtCOv; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf08.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1793112170; 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=xoLSuofN7cQ2tWXwUvc/DSgwxulevn9ENLUaotbNxMY=; b=WLoSQWC97kxZZ9q5NbtV8ey4W0SNY/B3zz1cVvTyETARd7kKk3m0pXc6LVDtbnPtIBPubT rKF0WSmzjeU7oz7XRUj61QvYNxZVAyv581Bd3ywmo2WjtADfLo/rRC3xk0hSkIy9MKw15X Dd/PtVOzagr7MLrYvFtpsk8ALPaOpPA= ARC-Authentication-Results: i=1; imf08.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=nCibtCOv; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf08.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1793112170; b=TKYv8JGTAUHk1haJLb88gZVVz+AyEepMorNwTh0p17xIDrVOUHVHJRDNbam2SRXOmLND2Y l+FpZbsPNPv3xJX6dY2Zc8BlFPHoZpOS0Zao8rHAJAXfEoRJgbIy4DdC71o364o8hm1Ls3 SbhMCVseJeTEJy4+1Y5b+udd+axj2UM= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id D8842602BE; Tue, 27 Oct 2026 14:42:49 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0F6B11F031E2; Tue, 27 Oct 2026 14:42:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793112169; bh=xoLSuofN7cQ2tWXwUvc/DSgwxulevn9ENLUaotbNxMY=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=nCibtCOvcqjhtwxq9rIemKZCtHNwaNf0BlFYC+FouftiBZosSYpxUL0mYyiauWLpd T2Y6UhXpbH0x1mHHjwNPbem/AT56EcTY0wEs4ibeYgTQGRswuJDpCv2LXbJ+CxbD6X a3MNJHAVtaQVmSxaDIlgWzSKkR19zx+tcBS53yPUPCaggBn1R319Y+LeTJTjoPQdt4 U9EtvqFBnxhwsG3bg1rjQB+ZU2EMtiGPYNKf8ulZoxR+zqhKLcr7A3W4el3jE2UZme ESkSApBkTcsYRn2/FolhS5eGkQDuIExsSFIm+G8gM1QCufx8s3kvrSwfMUkqaeUqZg 7DbTbx3UW5nSA== Message-ID: <829f5a0f-4d9a-4c65-9703-fbf6e49d2b02@kernel.org> Date: Tue, 27 Oct 2026 15:42:40 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 3/4] mm/huge_memory: read a special PMD under the lock in copy_huge_pmd() To: Konstantin Khorenko , Andrew Morton , Zi Yan , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Peter Xu Cc: Alex Williamson , kvm@vger.kernel.org, =?UTF-8?Q?Lo=C3=AFc_Molinari?= , Lorenzo Stoakes , Shuah Khan , linux-kselftest@vger.kernel.org, dri-devel@lists.freedesktop.org, Madhavan Srinivasan , "Ritesh Harjani (IBM)" , linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Jason Gunthorpe , Sashiko References: <20261021-b4-prep-vstor-149847-copy_huge_pmd-recheck-special-pmd-v4-0-66f00b7a564c@virtuozzo.com> <20261021-b4-prep-vstor-149847-copy_huge_pmd-recheck-special-pmd-v4-3-66f00b7a564c@virtuozzo.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: <20261021-b4-prep-vstor-149847-copy_huge_pmd-recheck-special-pmd-v4-3-66f00b7a564c@virtuozzo.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 6B978160006 X-Stat-Signature: 4rtyqxbutozxujgqo9g93ipq9wwb531b X-Rspamd-Server: rspam04 X-Spam-Status: No, score=-17.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1793112170-381077 X-HE-Meta: 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 ywjvZkcg 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 10/21/26 22:36, Konstantin Khorenko wrote: > copy_huge_pmd() reads a special PMD without the page table lock and > copies that value to the child. The mmap write lock held by fork does > not stop unmap_mapping_range(): it zaps under i_mmap_rwsem and the PMD > lock. > > The zap visits the parent VMA before the child's, as dup_mmap() links > the child right after the parent in i_mmap. If it clears the parent PMD > after fork has read it, and passes the child before fork copies it, the > child keeps a mapping the driver has revoked, for example: > > - vfio-pci: the child reaches the BAR after the device memory was > disabled or the device was reset, instead of getting SIGBUS; > - panthor: the child maps the pages of an evicted buffer object after > the driver has released them. > > The same branch deposits no page table under the copy. ppc64 in hash > mode keeps the hash slot array of every huge PMD in that table, so the > child dereferences a NULL table on the first hash fault, in > __hash_page_thp(), and on the zap, in hash__pmdp_huge_get_and_clear(). > > Take the locks first and let vm_normal_page_pmd() tell a PFN mapping > from a folio under them, as copy_present_ptes() does with > vm_normal_page(). The zap clears the parent PMD under the same lock, so > either fork finds it none and skips it, or the copy is in place before > the zap reaches the child. > > The copy of a PFN mapping then goes through the same tail as a folio: > > - it gets a page table where the architecture needs one; > - in a shared mapping it is marked clean in the child, as a PTE is; > - in a CoW mapping, which only VM_MIXEDMAP allows, both sides are write > protected instead of a warning being printed. > > Fixes: bc02afbd4d73 ("mm/fork: accept huge pfnmap entries") > Fixes: d1503aa9ab80 ("powerpc/64s: Add support for huge pfnmaps") > Reported-by: Sashiko > Closes: https://sashiko.dev/#/patchset/20261014-b4-prep-vstor-149847-copy_huge_pmd-recheck-special-pmd-v1-1-d225c60bc316@virtuozzo.com?part=1 > Suggested-by: David Hildenbrand > Signed-off-by: Konstantin Khorenko > --- > mm/huge_memory.c | 24 +++--------------------- > 1 file changed, 3 insertions(+), 21 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 13e3674fb6115..da5918a0ade87 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -1961,25 +1961,6 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm, > int ret = -ENOMEM; > bool writable; > > - pmd = pmdp_get_lockless(src_pmd); > - if (unlikely(pmd_present(pmd) && pmd_special(pmd) && > - !is_huge_zero_pmd(pmd))) { > - dst_ptl = pmd_lock(dst_mm, dst_pmd); > - src_ptl = pmd_lockptr(src_mm, src_pmd); > - spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING); > - /* > - * No need to recheck the pmd, it can't change with write > - * mmap lock held here. > - * > - * Meanwhile, making sure it's not a CoW VMA with writable > - * mapping, otherwise it means either the anon page wrongly > - * applied special bit, or we made the PRIVATE mapping be > - * able to wrongly write to the backend MMIO. > - */ > - VM_WARN_ON_ONCE(vma_is_cow_mapping(src_vma) && pmd_write(pmd)); > - goto set_pmd; > - } > - > if (vma_is_anonymous(dst_vma) || arch_needs_pgtable_deposit()) { > pgtable = pte_alloc_one(dst_mm); > if (unlikely(!pgtable)) > @@ -2021,7 +2002,9 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm, > goto copy_pmd; > } > > - src_page = pmd_page(pmd); > + src_page = vm_normal_page_pmd(src_vma, addr, pmd); > + if (!src_page) > + goto copy_pmd; > VM_BUG_ON_PAGE(!PageHead(src_page), src_page); > src_folio = page_folio(src_page); > > @@ -2061,7 +2044,6 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm, > } > if (src_vma->vm_flags & VM_SHARED) > pmd = pmd_mkclean(pmd); > -set_pmd: > pmd = pmd_mkold(pmd); > set_pmd_at(dst_mm, addr, dst_pmd, pmd); > > Looks correct. Reading the above, I wonder about Cc: stable. It would affect v6.12, so not too crazy to backport. We'd have to backport patch #2 as well in that case (or have a simpler fix, but I am not sure that's really worth it). Acked-by: David Hildenbrand (Arm) -- Cheers, David