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 174DB3F926F; Thu, 15 Oct 2026 15:48:24 +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=1792079317; cv=none; b=fshUkshs3ZLAjbPzuyebgSh0Vl0Zn2JMvkazy9u5TV8au0e15L5dNXECI33r5EXk3posJjOvB/DGYJ+1UXoxiH3OyCszMBhDN6n1kyCFA/GyktIv0nFRdTmqSXOE6M5iUop6unXeT3LjFlb5pMvbFxzPDKua45OadhVRjXjrY4M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792079317; c=relaxed/simple; bh=bnse//IfN9AFrQ0nl1qQiqrWgFN4uFypsLZ/htuIvqA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=q0qsclu6SrOkqXMjzCPoiNvuahDW+wBqLvJAMvFekV2HF6lRKeexlBCEUEvI+slMstd/+Wo8BGJZ5FHRaanFOOT8RTksalc0/8vHAAGcEWe4v0RSAQFff6GAw274tt/KmAl/kVlUZNH3fp/o2R7b1B6kfZtD3gbcOOc39E0eSLI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=NbmIPg3M; 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="NbmIPg3M" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7ACC11F000C4; Thu, 15 Oct 2026 15:48:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792079304; bh=KKYxbZUwVotNEVMIbNl0nivjJJ0OoZD4nTbemWC4y4M=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=NbmIPg3M1nE3t0SveamnjAch6hz4YUVyRo3Lmxk6mjby6t9kleTRe7gTyNUZe12ha BjmbVMW7+w4ZZvddeg1U7zVqRhplVFB9wY/dJAqnr+R2ILmqliDeTcA3Ybs2idt/lV OE89VnTiuroc9R8SkifPKah08UeOe2N0P2KB0Fn8gGFDdK5HfbExVOqzUwRgogXy6E 8QyG2sd+NB4s/CQZ6vfBb58ay703XtCQikPZg26WCfpxVlz3HYRClHZMYZhpiZkjOR vPDpyuTg1N1+kr0dBXwFTuGczz3D1mza4v6BO2/XjwW7RkDNe2ii8ejQsMC3Dg0xHo XshQYVliATdCw== Message-ID: <79b299ac-a588-43e1-af46-e69d8b3e7aca@kernel.org> Date: Thu, 15 Oct 2026 16:15:33 +0200 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 2/2] mm/huge_memory: deposit a page table for a special PMD copied by fork 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?= , 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 , stable@vger.kernel.org References: <20261014-b4-prep-vstor-149847-copy_huge_pmd-recheck-special-pmd-v3-0-85eaec8417f6@virtuozzo.com> <20261014-b4-prep-vstor-149847-copy_huge_pmd-recheck-special-pmd-v3-2-85eaec8417f6@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: <20261014-b4-prep-vstor-149847-copy_huge_pmd-recheck-special-pmd-v3-2-85eaec8417f6@virtuozzo.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/14/26 17:46, Konstantin Khorenko wrote: > Where arch_needs_pgtable_deposit() is true, every huge PMD needs a > deposited page table. ppc64 in hash mode keeps the hash slot array of > the huge page in it, so vmf_insert_pfn_pmd() deposits one for each > special PMD it maps. > > copy_huge_pmd() copies a special PMD into the child without a table. > The child then dereferences a NULL table: > > - on the first hash fault on the PMD, in __hash_page_thp(); > - on the zap at munmap() or exit, in hash__pmdp_huge_get_and_clear(). > > Allocate a table before taking the page table locks and deposit it > with the copy, as insert_pmd() does. > > Fixes: d1503aa9ab805 ("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 > Cc: stable@vger.kernel.org > Assisted-by: LLM > Signed-off-by: Konstantin Khorenko > --- > mm/huge_memory.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index bf788bb231691..2380e4e877f82 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -1961,6 +1961,11 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm, > pmd = pmdp_get_lockless(src_pmd); > if (unlikely(pmd_present(pmd) && pmd_special(pmd) && > !is_huge_zero_pmd(pmd))) { > + if (arch_needs_pgtable_deposit()) { > + pgtable = pte_alloc_one(dst_mm); > + if (unlikely(!pgtable)) > + goto out; > + } > dst_ptl = pmd_lock(dst_mm, dst_pmd); > src_ptl = pmd_lockptr(src_mm, src_pmd); > spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING); > @@ -1974,6 +1979,8 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm, > if (unlikely(pmd_none(pmd))) { > spin_unlock(src_ptl); > spin_unlock(dst_ptl); > + if (pgtable) > + pte_free(dst_mm, pgtable); > return -EAGAIN; > } > /* > @@ -1983,6 +1990,10 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm, > * wrongly write to the backend MMIO. > */ > VM_WARN_ON_ONCE(vma_is_cow_mapping(src_vma) && pmd_write(pmd)); > + if (pgtable) { > + mm_inc_nr_ptes(dst_mm); > + pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable); > + } > goto set_pmd; It's another sign that the pmd_special() is just entirely misplaced. Let's get that sorted and it will just naturally fix the other case. -- Cheers, David