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 004104F3ED2 for ; Fri, 9 Oct 2026 18:05:20 +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=1791569122; cv=none; b=DOQzp1TakUS9bdWDBMpwD3tzycYeWSTOx6VvFobp0tC9V5r9emFZeu8m7iUUx5N/rqWWOnXOXUc4ws0FrqSwcrnYq+iabCeg7USBKtKsanC0V/+9RTkp12oy8mT+ExNmGXfdAPilEPffLU85c6oDdZrjTSoRd0m5NWMNDF/QKmE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791569122; c=relaxed/simple; bh=si334WCVwj1yQ+s6d1lKducAmYLBcj1iekwRL1qoJKo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=i8LRKhSe/3vbNk3/rLZoVKdtyO3HCv6pV2y5i/ydpLCTSHcsIUG1p/V8hnkK+/pYLiX7seM/6D9vkk62Mt1wFWdg7yslRmX9vIBoRntY9D8btzW6EGvACQxMYZ6IcllqSYJ+55wyTPaL8Eiv2LpZmSpXGBpqC00ixzcTRiTfVpA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=L3qLqNhV; 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="L3qLqNhV" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 555DD1F000FF; Fri, 9 Oct 2026 18:05:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791569120; bh=hpQ3dp10EQMwRCwD3eHi09l9cQIxAnlp034y5giT03s=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=L3qLqNhVtAqtRoH4KUKA4HjzDT34jcPjxFQtiO1J8Nz81ipPOTkmO7dW5K25SPdWj sxkVyQLqCCRKN1anhjgC3Xg3gLLqyYnweHUAgNKkgIt86WoenigAEg8fz4nIIGDKll o8E7rTbSWXn9ksG7T+4KM+oB+h4hZMyJUqptZrQcA70sdLLPiuLLkRnP3YwTEh8A/B QvuEjRjT3Y2XSofKnX0MzECCYwPHhCkW7ymdx43djTrsdE0la4fqB5kEP6FLP1UZ9Y yHwY+3/cIY3HqzeqbYe+nF/+sanQcHq3pNQfMjHPYFajDavk5rX5rlwbQB0M65KmnC UqcDlhX7aQgRA== Message-ID: <70ea8ee6-6fc5-4209-8cee-362da37f5035@kernel.org> Date: Fri, 9 Oct 2026 20:05:15 +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/hugetlb: avoid recursive i_mmap_rwsem in PMD sharing To: "Lorenzo Stoakes (ARM)" Cc: Li Zhe , "Jose A. Perez de Azpillaga" , akpm@linux-foundation.org, muchun.song@linux.dev, osalvador@suse.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260930064308.58159-1-lizhe.67@bytedance.com> <9a7c026e-f5f2-40e0-84aa-919c988cc136@bytedance.com> <2b4571c5-8e51-4c91-9d88-11929f200875@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 10/9/26 13:52, Lorenzo Stoakes (ARM) wrote: > On Mon, Oct 05, 2026 at 11:25:01AM +0200, David Hildenbrand (Arm) wrote: >>> David mentioned that Oscar was planning to send a proper fix for this >>> issue, so I will wait for that patch instead of moving forward with this >>> trylock fallback approach. >> @Lorenzo, if Oscar is too busy, I guess we can paste the overall idea for the >> fix here as well (publicly)? > > Yeah I don't see why not! I don't think there's anything that needs to be > private here. Li, see below, can you work with the below? ----8<---- >From 9e1c0676ea6c9cbcabf91cd8badf81a9d88fd3ef Mon Sep 17 00:00:00 2001 From: "Lorenzo Stoakes (ARM)" Date: Wed, 29 Jul 2026 18:33:08 +0100 Subject: [PATCH] fix --- mm/hugetlb.c | 103 +++++++++++++++++++++++++++++++++++++++------------ 1 file changed, 79 insertions(+), 24 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index e93c4d2456aa..88ff2c4ad483 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -5077,6 +5077,79 @@ static void move_huge_pte(struct vm_area_struct *vma, unsigned long old_addr, spin_unlock(dst_ptl); } +/* Returns last address processed */ +static unsigned long prealloc_or_move_page_tables(struct vm_area_struct *vma, + struct vm_area_struct *new_vma, unsigned long old_addr, + unsigned long new_addr, unsigned long len, unsigned long sz, + unsigned long last_addr_mask, struct mmu_gather *tlb, + bool is_prealloc) +{ + unsigned long old_end = old_addr + len; + struct hstate *h = hstate_vma(vma); + struct mm_struct *mm = vma->vm_mm; + pte_t *src_pte, *dst_pte; + + hugetlb_vma_assert_locked(vma); + + for (; old_addr < old_end; old_addr += sz, new_addr += sz) { + src_pte = hugetlb_walk(vma, old_addr, sz); + if (!src_pte) { + old_addr |= last_addr_mask; + new_addr |= last_addr_mask; + continue; + } + if (huge_pte_none(huge_ptep_get(mm, old_addr, src_pte))) + continue; + + if (is_prealloc) { + if (!huge_pte_alloc(mm, new_vma, new_addr, sz)) + break; + continue; + } + + if (huge_pmd_unshare(tlb, vma, old_addr, src_pte)) { + old_addr |= last_addr_mask; + new_addr |= last_addr_mask; + continue; + } + + dst_pte = hugetlb_walk(new_vma, new_addr, sz); + if (!dst_pte) + break; + + move_huge_pte(vma, old_addr, new_addr, src_pte, dst_pte, sz); + tlb_remove_huge_tlb_entry(h, tlb, src_pte, old_addr); + } + + return old_addr; +} + +/* Returns true if preallocation succeeded across range, otherwise false. */ +static bool prealloc_hugetlb_page_tables(struct vm_area_struct *vma, + struct vm_area_struct *new_vma, unsigned long old_addr, + unsigned long new_addr, unsigned long len, unsigned long sz, + unsigned long last_addr_mask) +{ + unsigned long old_end = old_addr + len; + unsigned long addr_end; + + addr_end = prealloc_or_move_page_tables(vma, new_vma, old_addr, new_addr, + len, sz, last_addr_mask, NULL, /*is_prealloc=*/true); + + return addr_end >= old_end; +} + +/* Returns last processed address. */ +static unsigned long __move_hugetlb_page_tables(struct vm_area_struct *vma, + struct vm_area_struct *new_vma, unsigned long old_addr, + unsigned long new_addr, unsigned long len, unsigned long sz, + unsigned long last_addr_mask, struct mmu_gather *tlb) +{ + i_mmap_assert_write_locked(vma->vm_file->f_mapping); + return prealloc_or_move_page_tables(vma, new_vma, old_addr, new_addr, + len, sz, last_addr_mask, tlb, /*is_prealloc=*/false); +} + int move_hugetlb_page_tables(struct vm_area_struct *vma, struct vm_area_struct *new_vma, unsigned long old_addr, unsigned long new_addr, @@ -5088,9 +5161,9 @@ int move_hugetlb_page_tables(struct vm_area_struct *vma, struct mm_struct *mm = vma->vm_mm; unsigned long old_end = old_addr + len; unsigned long last_addr_mask; - pte_t *src_pte, *dst_pte; struct mmu_notifier_range range; struct mmu_gather tlb; + bool preallocated; mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, old_addr, old_end); @@ -5106,30 +5179,12 @@ int move_hugetlb_page_tables(struct vm_area_struct *vma, last_addr_mask = hugetlb_mask_last_page(h); /* Prevent race with file truncation */ hugetlb_vma_lock_write(vma); + preallocated = prealloc_hugetlb_page_tables(vma, new_vma, old_addr, + new_addr, len, sz, last_addr_mask); i_mmap_lock_write(mapping); - for (; old_addr < old_end; old_addr += sz, new_addr += sz) { - src_pte = hugetlb_walk(vma, old_addr, sz); - if (!src_pte) { - old_addr |= last_addr_mask; - new_addr |= last_addr_mask; - continue; - } - if (huge_pte_none(huge_ptep_get(mm, old_addr, src_pte))) - continue; - - if (huge_pmd_unshare(&tlb, vma, old_addr, src_pte)) { - old_addr |= last_addr_mask; - new_addr |= last_addr_mask; - continue; - } - - dst_pte = huge_pte_alloc(mm, new_vma, new_addr, sz); - if (!dst_pte) - break; - - move_huge_pte(vma, old_addr, new_addr, src_pte, dst_pte, sz); - tlb_remove_huge_tlb_entry(h, &tlb, src_pte, old_addr); - } + if (preallocated) + old_addr = __move_hugetlb_page_tables(vma, new_vma, old_addr, + new_addr, len, sz, last_addr_mask, &tlb); tlb_flush_mmu_tlbonly(&tlb); huge_pmd_unshare_flush(&tlb, vma); -- 2.55.0 -- Cheers, David