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=1793283888; b=wjA+66V56OVCYdpe3hMMkmo9kQass2mSS/1AXe1bX6gLi7B6iHLNL0uxXU10L1bS4y6X oso/TBvcicSX1AabDvf0Q9pScaAONpDVkFd+e3F7FCCM3qcNUE90uRdt5Hu4YDk/d2MVI Io4A/3seZWAa23SYAgZgnDE9z1G4pfkTmnWOOELJjh5CNp/RRqqCD3GR8pvYaAz1s1KsY JLs3Uk+iuuNLnJQsm2V1lKp+nBd1r2TKMZoIxw5u/EuwYvsPzwr63dk3jROPs0Tm+Xjz2 aw3eWkH4wiIkm6L5Xp2qRsAJZGOkvE/zGSB83Ab5Hrl/0SL5Q+OPZA86a+QIuAWQw4w== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793283888; 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=SxkkcfsluS6d+NVCz2poz3Y5Si8QKMa7Ic0pVGQHkyk=; b=WHtYOVUs97qa4/oDQjl9UDU+6/ardyKGwfeEqVbWCDOZaVGTmX+HOta9+0XiZxq5Gwg3 19nXIL1w3OFfk8jhDxU7/fklxdaZJ10bB27qwaG03TFpIiiPT1CLY05AXD7BUmNc7sPC7 nWq2EGaQEZvfOwX+4oT/LjG6XR8t2eBHcjjeh/WMClc/g1V0LS6YAKTvehyoizZn3LzH9 PakOoFsE6K7/diAdCPPG5nyzF38uDhwmS6P29/FUK/fZyC3/HSyOm5u4keiQ3JHAlzdrR pFx99P14whaDsCw6SoGtWXicMq2aOuFdpLsKO4Kn7xj9Ky3OYOxPBeuzEJbaum+aytQ== 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=OteUheN2; 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 A37E8606A31E; Thu, 29 Oct 2026 14:24:47 +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=OteUheN2 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0FE3F1F01825; Thu, 29 Oct 2026 14:24:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793283887; bh=SxkkcfsluS6d+NVCz2poz3Y5Si8QKMa7Ic0pVGQHkyk=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=OteUheN2B32bcN/9f5UfOzNiidLI5B9Hm8n+cfKENxQbbyPjAfgEMmAWpOox7ULf9 ADd38P2P44AqXSb4hgJKIJJDlmNn2Apmwre5vkrE6g+eEXgL+CVK/idHVFGO+OtJkn t6RxcY2eYwnapJ5IuPh/5zax4sVLJj3IEFkePyURCFjWkkAQqrNgdgffbKpO9oqgb/ +PQosj7oDILNllKB6L2+ZbiVwSryf1sa9VQDCaS+zZZUTej5L/1oj3MuBsIRhtR2U2 00APFSv+H7Z5hunV3cf6MkVbD6jPPuCCb27PyQXie7gQ//fYDIyQmQXkEjiGBxEWVY L3K14QXYNVLzg== Message-ID: <9f4128a4-85fc-4f4b-ac41-b9d348f56e37@kernel.org> Date: Thu, 29 Oct 2026 15:24:29 +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 42/46] mm/huge_memory: split huge PUDs when adjusting VMA boundaries To: Kiryl Shutsemau 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 , Pedro Falcato , 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 , 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, stable@vger.kernel.org References: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> <20261027-fixes_core-v1-42-6f74bec9a5bb@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 10/29/26 12:45, Kiryl Shutsemau wrote: > On Tue, Oct 27, 2026 at 12:18:02AM +0100, David Hildenbrand (Arm) wrote: >> PFN mappings such as VFIO PCI BAR mappings can use PUD leaves while >> allowing VMA splits at page granularity. However, vma_adjust_trans_huge() >> only handles PMDs. >> >> After faulting a writable PUD-sized VFIO BAR mapping, changing its first >> page to read-only with mprotect() makes the PMD walk treat the PUD leaf >> as a PMD table. Applying MADV_DONTFORK to the first PMD-sized chunk leaves >> the PUD spanning two VMAs: the PMD-aligned boundary skips splitting. >> >> Walk the page tables once at each adjusted boundary and split a huge >> PUD or PMD leaf as needed. Handle PUD leaves even when the boundary is >> PMD-aligned. >> >> Fixes: f9e54c3a2f5b7 ("vfio/pci: implement huge_fault support") >> Cc: stable@vger.kernel.org >> Signed-off-by: David Hildenbrand (Arm) >> --- >> mm/huge_memory.c | 70 ++++++++++++++++++++++++++++++++++++++++++++++++-------- >> 1 file changed, 60 insertions(+), 10 deletions(-) >> >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index 08e58cda7d37d..d090642ac8c2b 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -3503,16 +3503,66 @@ void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, >> __split_huge_pmd(vma, pmd, address, freeze); >> } >> >> -static inline void split_huge_pmd_if_needed(struct vm_area_struct *vma, unsigned long address) >> +static bool pud_split_required(const struct vm_area_struct *vma, >> + unsigned long address) >> { >> + if (!IS_ENABLED(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD)) >> + return false; >> + if (IS_ALIGNED(address, HPAGE_PUD_SIZE)) >> + return false; >> /* >> - * If the new address isn't hpage aligned and it could previously >> - * contain an hugepage: check if we need to split an huge pmd. >> + * Only selected VMAs support mapping PUDs for now. Lift the >> + * restriction once this changes. >> */ >> - if (!IS_ALIGNED(address, HPAGE_PMD_SIZE) && >> - range_in_vma(vma, ALIGN_DOWN(address, HPAGE_PMD_SIZE), >> - ALIGN(address, HPAGE_PMD_SIZE))) >> - split_huge_pmd_address(vma, address, false); >> + if (!vma_is_dax(vma) && !vma_test_any(vma, VMA_PFNMAP_BIT, VMA_MIXEDMAP_BIT)) >> + return false; >> + return range_in_vma(vma, ALIGN_DOWN(address, HPAGE_PUD_SIZE), >> + ALIGN(address, HPAGE_PUD_SIZE)); >> +} >> + >> +static bool pmd_split_required(const struct vm_area_struct *vma, >> + unsigned long address) >> +{ >> + if (IS_ALIGNED(address, HPAGE_PMD_SIZE)) >> + return false; >> + >> + return range_in_vma(vma, ALIGN_DOWN(address, HPAGE_PMD_SIZE), >> + ALIGN(address, HPAGE_PMD_SIZE)); >> +} >> + >> +static void split_huge_leaf(struct vm_area_struct *vma, >> + unsigned long address) >> +{ >> + const bool split_pud = pud_split_required(vma, address); >> + const bool split_pmd = pmd_split_required(vma, address); >> + pgd_t *pgd; >> + p4d_t *p4d; >> + pud_t *pud; >> + pmd_t *pmd; >> + >> + /* >> + * mmap, VMA and rmap write locks protect the walk; the split helpers >> + * take the page table locks. >> + */ >> + if (!split_pud && !split_pmd) >> + return; >> + >> + pgd = pgd_offset(vma->vm_mm, address); >> + if (!pgd_present(*pgd)) >> + return; >> + >> + p4d = p4d_offset(pgd, address); >> + if (!p4d_present(*p4d)) >> + return; >> + >> + pud = pud_offset(p4d, address); >> + if (split_pud && pud_leaf(*pud)) >> + __split_huge_pud(vma, pud, address); >> + if (!split_pmd || !pud_present(*pud)) >> + return; > > This looks wrong. > > We should bail out here if PUD is was a leaf and wasn't split. __split_huge_pud() must split a leave. Either by zapping it (what we do right now) or by populating page tables (as in Usama's PoC). We can throw in here a if (WARN_ON_ONCE(!pud_leaf(pud))) return; But I don't see how that would be required. If we run into an un-splittable PUD something else is completely messed up. (this is not hugetlb code :) ) -- Cheers, David