From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 1F1B633F589; Tue, 28 Apr 2026 05:37:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777354632; cv=none; b=kDgzKaoX7eCE+bwmzjdI78A5FV7aPHmY9sIdU0eUdTr00Q2rULBLSdKQNcexeTbKQ00yKFwdaQ+g6yEi1WvbLXaXY1KhZlNAOflhkU2+38CDb2ePcP1ZFOGxe8Sbp8tncRskIRYsjEcDBWWa/I9JP8Autwy2I6MES8GeecohOhQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777354632; c=relaxed/simple; bh=35j+qmt6iWL15WfQJe5Xfl8qePbfDGAdSt+9hvpfQxM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=SiSzv4rIxflCaN54ujTxgBIBje0RdZbnHPjE2grD0a9FcfvqCTx6dltBu6VzDyWNE7GzfOqnEBvmPm84n6GbfiBlU2iU0TSz3GCYlXHER4BMeQKqJqP5rDo8HBURI7sS75ZRI/iAcY6KrHwx+VtyrUkvSjME41w60Xsu1vu9HBs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Ljwpku2y; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Ljwpku2y" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 41145C2BCAF; Tue, 28 Apr 2026 05:37:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777354631; bh=35j+qmt6iWL15WfQJe5Xfl8qePbfDGAdSt+9hvpfQxM=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Ljwpku2ytv1a51/lWJ0in9sBUOvx/MFmaVm2lPWSgv9iXQ5Y5hi97v5lXatAQMj+o M6v48RpZX+/yodaSIkctR7XFA621nSVRkUAHLndGlPCH/3+0raZFnmvzHx6QFrbUSW MY2nLUR0beFVJYiZhHeXViYGYrVhJqildv0ZoE5dhL7L/xaz7W4ZNKOYDsAGmVW63b OBYu3z+Z+i9ktOYlazQVUXbybAFNByZdkO1qb2CjKEvkk9cyFBQIJt9meREV7C2c4Q pi2MNJfmfmSD0V3v0rlTi2dKaJpC9vRYnsWEHGQFNmGUTXSaHRe4IbR4Mphemz8+Vq ZokFl+wxATNAA== Message-ID: <06d11ed8-8532-4748-8ce2-6715c4665dc5@kernel.org> Date: Tue, 28 Apr 2026 07:37:00 +0200 Precedence: bulk X-Mailing-List: linux-sh@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/3] mm: remove page_mapped() To: Alexei Starovoitov Cc: Yoshinori Sato , Rich Felker , John Paul Adrian Glaubitz , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Kumar Kartikeya Dwivedi , Song Liu , Yonghong Song , Jiri Olsa , Andrew Morton , Lorenzo Stoakes , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Rik van Riel , Harry Yoo , Jann Horn , Matthew Wilcox , "Liam R. Howlett" , linux-sh@vger.kernel.org, LKML , bpf , linux-mm , Ryan Roberts References: <20260427-page_mapped-v1-0-e89c3592c74c@kernel.org> <97192ac3-643d-4393-87ef-53a9f3ddaf95@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: 8bit On 4/27/26 23:38, Alexei Starovoitov wrote: > On Mon, Apr 27, 2026 at 9:59 PM David Hildenbrand (Arm) > wrote: >> >> On 4/27/26 13:43, David Hildenbrand (Arm) wrote: >>> While preparing my slides for an LSF/MM talk, I realized that I did not >>> yet remove page_mapped(). >>> >>> So let's do that. In the BPF arena code it's unclear which memdesc we >>> would want to allocate in the future: certainly something with a >>> refcount, but likely none with a mapcount. So let's just rely on >>> the page refcount instead to decide whether we want to try zapping the >>> page from user page tables. >>> >>> Signed-off-by: David Hildenbrand (Arm) >>> --- >> >> I scanned AI review and I think it founds something that is not related to this >> patch. >> >> We use the page_mapped()->page_ref_count() check as an optimization to avoid >> calling zap_vma_range(). We must be able to call it even without that optimization. >> >> Just like the bulk zap call earlier >> >> if (page_cnt > 1) >> /* bulk zap if multiple pages being freed */ >> zap_pages(arena, full_uaddr, page_cnt); >> >> It talks about concurrent "munmap(), unmap_region() executes unmap_vmas()" >> racing with our zap_vma_range(). >> >> Looking into the details, arena_map_mmap() calls remember_vma(). We reject >> mremap and VMA split. arena_vm_close() removes the VMA from the list. The >> arena->lock protects our VMA list. >> >> So in zap_pages, the VMA cannot go away. If we find a VMA, ->close could not >> have been called yet. >> >> In vma.c, we call remove_vma() after vms_clear_pte(). So after unmapping the >> pages and freeing the page tables. >> >> So munmap() can indeed race with zap_vma_range(), and the page_mapped() check >> would not have changed anything about that really. >> >> >> @BPF folks: does BPF take anywhere the mmap lock in read mode before calling >> zap_vma_range()? It should do that. > > Yes, but do NOT. In general, do NOT talk to me like that. As I discussed recently with Ryan, we should update the locking requirements for zap_vma_range(). I assume friendly BPF folks will take care of fixing this. -- Cheers, David