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=1793011812; b=lZNXbhl60bT3qLogvUw9WYIzzKyMWueC0fLBEhqg2xIiDA33OGF23JEkKfR/dRhB3hD/ Nd53YATPXlQoQIB43uepgK132or3Hoobkk3ruHRjDoYXOKCtLS4gA8hFoBM4plaO//j6c qxnonAjZQamqee2RbSQ9Z7cVXE2GENeQhES0V06SKV/wgOq547uuwRoz2EYcZIS5E2oIe vrSz8LPmPB5ScrTDtF9j0xuUNRmNPvrhE8hJH0HckYjalZV0j8JQc0yZsIuuAmpFtYKDw 0W4fSehNG0ki1I9iA0SlC/6acjv6ziqDVtwlp/gvM5w5cAnbh1NMU82Q9OKCo/Gfgrg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793011812; 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=DY0xynj2BuvcQfpKNa55nqUlTfhCGDJICJ4nB0KZOrU=; b=aE1iWFqNM4Xl78musezdPDSb8bBFr7aHiweO/K9yBtoDUVozYprHoUWB+eZG7VaXZlvO UOGOhSlbf5UfzAcGOf1YAHRMD5EvrNXOtvTNkUo0ZTaUmsVT1FxjAInyc3Qt9Dw2cGVPN g/GPhYI+PKnYQ2OpipSEd8mEF+KPImzLfR8Jnul0J9J+EOMdWZaO8l2ePI5daeWeOPZrh C1+gv5KZP1SapPmEsRIv6m4VFbz1meMJ1v/Z7vpz3U2nDEzIouz9bDWpHM1v8KTp+mTpI U+kTBVAdEhn2s1zRb25kDGnZHqcDIoL7rQzYVkTM4QkNVp79nLvEduGONLD49EMtBmg== 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=ZNFcno64; 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 BE40C606A31A; Mon, 26 Oct 2026 10:50:11 +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=ZNFcno64 Received: by smtp.kernel.org (Postfix) with ESMTPSA id C2FE81F01825; Mon, 26 Oct 2026 10:50:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793011811; bh=DY0xynj2BuvcQfpKNa55nqUlTfhCGDJICJ4nB0KZOrU=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=ZNFcno64kcHcB3X4mVYYrxBv6nlifsAlqGJwZNpBSt89J4pheTzEFoPBx8BP+zofr bPQqcGJFRbvVc985BAtUDlnk+BrJp2u0Kb1izuHqHiSZGuhXGsINGHIRWwnwuPYfN/ E8NIXTXtMAkqWs+VuMMyEAmCvDeX+uppHya/sZ1qPAYBavFbrfhS9LZHa6R0+/8Uao 3DmUVVx90fJ7JBoYn0vVeywHxkBpBWxVW8F9vaQ/N2CYwVfQCIawH9oZ4AP3E5LJgq r9lCBAqTGt/YUYsnZif3SUiyGnC7bii7/H8bQh0gw9kzDJq+aqbwJpoa/hhnL/KEtj EQr9PhCLWUh4w== Message-ID: Date: Mon, 26 Oct 2026 11:50:04 +0100 X-Mailing-List: linux-kernel@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 4/4] mm/vma: avoid losing atomic VMA flags when setting sticky VMA flags To: "Lorenzo Stoakes (ARM)" , Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato , Davidlohr Bueso , SJ Park , Kees Cook , Colin Cross Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20261023-fix-vma-atomic-v1-0-8ff4fae1fc85@kernel.org> <20261023-fix-vma-atomic-v1-4-8ff4fae1fc85@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: <20261023-fix-vma-atomic-v1-4-8ff4fae1fc85@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/23/26 15:47, Lorenzo Stoakes (ARM) wrote: > vma_merge_existing_range() merges an existing VMA (middle) when its > attributes have changed to match those of one or both adjacent VMAs. > > Sticky flags are propagated if they are set in any of the merged VMAs. They > are initialised from vmg->vma_flags, which is assumed to contain middle's > sticky flags when the function is invoked. > > However, the VMA write lock is not held for middle when they are first > populated, so concurrent updates to atomic VMA flags may occur, which will > be lost upon merge. > > This can result in fork failing to propagate guard region markers and (if > file-backed) THP collapse discarding them. > > Resolve this by propagating the sticky flags after middle is locked. > > Make life easier by factoring this into propagate_sticky_flags(), which > treats vmg->vma_flags as its base (in case any sticky flags are set there), > updating it as sticky flags are accumulated from merged VMAs. > > Also update vma_expand() to use propagate_sticky_flags() so all merge paths > utilise it. > > propagate_sticky_flags() also asserts that the VMA write lock is held for > the VMA whose sticky flags are being read, with a comment explaining why. > > Another means by which atomic VMA flags can fail to be observed is when the > merge is finalised in commit_merge(). > > rmap locks are dropped in vma_complete() before the sticky flags are > written, meaning an rmap walker can observe the VMA without sticky flags > set, which can also result in retract_page_tables() discarding guard > markers. > > Resolve this by assigning the sticky flags before dropping rmap locks, > factored into commit_sticky_flags() with a write assert on the VMA being > written to. > > Also remove the vma_set_flags_mask() invocation at the end of > vma_merge_existing_range() as this was introduced by commit > 64212ba02e66 ("mm: implement sticky VMA flags") to propagate sticky flags, > which is now redundant with the introduction of commit_sticky_flags(). > > The vma_set_flags_mask() invocation at the end of vma_expand() setting > sticky flags only is also removed for the same reason. > > Also update vma_merge_existing_range()'s comment to reflect the fact that > vmg->vma_flags gets updated. > > Finally, update the userland VMA tests to reflect a previously missed > const-ification in vma_assert_write_locked() which would otherwise cause a > warning when building them. > > Suggested-by: David Hildenbrand (Arm) > Fixes: 2ab7f1bbafc9 ("mm/madvise: allow guard page install/remove under VMA lock") > Fixes: 49e14dabed7a ("mm: set the VM_MAYBE_GUARD flag on guard region install") > Cc: > Signed-off-by: Lorenzo Stoakes (ARM) > --- Nothing jumped at me Acked-by: David Hildenbrand (Arm) -- Cheers, David