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=1793898420; b=2+BObUHXi5LHOu1/+oAy3mbXHbNn4grZZVxVx0nYWNy+grJ2KI9VW8zZAACIJrOawUAb 35+ogWEJsKQ32XZvZeYcAqHmSRVOYqOkFZf8gg7YrObYJ8KMphey1yMXLpGsEsUM32bY/ AVwv42s+xXVI3exPVRxvffxgVbDdqBTVamN7WwOwO6sSHf2ZslP+BF/uKnM2Rb+WXWthW L04plGbzaD0emxgT4PJOKT0rLMktUuCv63BDyEaE8k3M9Pxk0jYy8KLim9Q+GfH6dPEgV j8Nl6xkRG15F5Ueuq7ypB2WBO5sjQ8Hdo8yhrPGhjUU5+ItK8dUWvGjA/87y4Kz7H9g== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793898420; 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=+BKEtapVg9ZvVExUrrwjchlBg9HiJLaq+cPGzmG6490=; b=vzSHu+RXWleNxIuzuN8YX7aR76zN6kT01Wg6WPuxMpuqmQ5HmZsV296kP7WgIArjJfg1 5uUC5RfvBE1yKcCRd0qMiUjoSjpfuj76L2zf7t4BdSjfqD8DLAtl1IBPo8K4v2v55FLgf aoMj5TwQFcoC5YQ+mpB6UuK/hC4lmPeXM8s65EVnxa2kGnm+8VLgY6V5z2asKUMAfYjPt imLPalho1JbbSksGSH+oHhmM7ys3L2ovTGFLHMORHXYBanvHCcib1PR50JsI87zgac+ff /za6gNOOh8n7PVe/MTFCIXEqDNINoBRCUH6sDnKb1eD++6e6CvvZPVV6Vy89TgFVnVg== 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=nCBJ4Wja; 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 822BA606A328; Thu, 5 Nov 2026 17:07:00 +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=nCBJ4Wja Received: by smtp.kernel.org (Postfix) with ESMTPSA id C36961F000C1; Thu, 5 Nov 2026 17:06:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793898420; bh=+BKEtapVg9ZvVExUrrwjchlBg9HiJLaq+cPGzmG6490=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=nCBJ4WjaV9h7VqVSkn+QKi1XYE0fRlYAYNMppPShoj71GS4tfxkkkZwdzDtxKAKKl r0jtdIYZA2tq51uKkJAA13EqrgdCxvdUluOASXfXnfu1CRG2qZr5IuDwogdQzQNzQA y6zVuI1EE+wXeR4KVNis97tkbm05Kqpcp0c0e0xgJKQp9WypE2FyKaaISltCHvtAMI DJvnfFo2MpFIgEuBmbVBX/x0EEgTAANTpwoQC+6dN5AQS7FlQ6udIY0JtXubxV//jH E13rtGeBQqTBb5vbueganPKWeP54WeJDqCuNi19/YwwAadmoojigQ0slNYvhOOnCwB B/Y4ZkDZEcZyw== Message-ID: <60c4f0a0-e3c9-42dc-b2e0-0860ab6e30f0@kernel.org> Date: Thu, 5 Nov 2026 18:06:51 +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 v2 5/9] mm/mprotect: keep writable entries writable on permission upgrades To: =?UTF-8?Q?Carlos_L=C3=B3pez?= , kvm@vger.kernel.org, linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, linux-riscv@lists.infradead.org, seanjc@google.com, pbonzini@redhat.com, akpm@linux-foundation.org, peterx@redhat.com, ljs@kernel.org, imbrenda@linux.ibm.com, borntraeger@linux.ibm.com, frankja@linux.ibm.com, Zi Yan , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato References: <20261105165004.2663799-4-clopez@suse.de> <20261105165004.2663799-9-clopez@suse.de> 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: <20261105165004.2663799-9-clopez@suse.de> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 11/5/26 17:50, Carlos López wrote: > change_protection() applies vma->vm_page_prot, which lacks the write bit > for CoW and write-notified mappings, so it write-protects every entry > in them. When an entry would simply be made writable on fault without > further checks (e.g. dirty PTEs in shared mappings, exclusive anonymous > pages), MM_CP_TRY_CHANGE_WRITABLE makes the entry writable again to > avoid the future fault. > > However, writable entries in shared mappings that are not dirty still > become read-only. For example, a uffd-wp unprotect makes clean shmem > PTEs read-only even if they were never write-protected, e.g. when they > were mapped by a read fault before uffd-wp was registered. The next > write to each of them causes a fault that only restores the write bit. > > Now that MM_CP_PERM_UPGRADE indicates whether mprotect() only adds > permissions, change_protection() can tell, together with the > userfaultfd unprotect flags, when a change revokes no access. Keep > writable entries writable in these cases, at the PTE, PMD and PUD > levels. This is consistent with the write fault handler, as an entry > that is already writable needs no write fault. > > Signed-off-by: Carlos López > --- > mm/huge_memory.c | 7 +++++++ > mm/internal.h | 7 +++++++ > mm/mprotect.c | 4 ++++ > 3 files changed, 18 insertions(+) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 506e1e61c0fd..6e23d0e4ae66 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2809,6 +2809,10 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, > if (userfaultfd_rwp(vma) && pmd_uffd(entry)) > entry = pmd_modify(entry, PAGE_NONE); > > + /* See change_present_ptes(). */ > + if (mm_cp_is_perm_upgrade(cp_flags) && pmd_write(oldpmd)) > + entry = pmd_mkwrite(entry, vma); > + > /* See change_pte_range(). */ > if ((cp_flags & MM_CP_TRY_CHANGE_WRITABLE) && !pmd_write(entry) && > can_change_pmd_writable(vma, addr, entry)) > @@ -2885,6 +2889,9 @@ int change_huge_pud(struct mmu_gather *tlb, struct vm_area_struct *vma, > */ > oldpud = pudp_invalidate(vma, addr, pudp); > entry = pud_modify(oldpud, newprot); > + /* See change_present_ptes(). */ > + if (mm_cp_is_perm_upgrade(cp_flags) && pud_write(oldpud)) > + entry = pud_mkwrite(entry); That looks completely hacked on. We do have can_change_pud_writable() below to make such decisions. Whaatever you propose here is either wrong or way too shaky, sorry. -- Cheers, David