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 286133F65FF; Mon, 27 Apr 2026 20:59:35 +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=1777323576; cv=none; b=tJv8DXXL5lEY8nI/dW51IsS5LaNsIKI0HJnH8oIj9fTlZZRNBnDPgowMRyZ5iTu5wF3eI7iWSpVDf+tTa6Ezo/dmPgxGTUPOoaB5uN8iEpBEjrPHfcP3Bm5ur15R9SaAnaCgQqPHZKcTQhfVnaE4q6OmVnAXJO4lxOJ3sBbHlF0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777323576; c=relaxed/simple; bh=4fCdoQX9tOKa3DEv8CT8f6q/tReZla5dySYrHKOPds8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=R7GaAxRmFTDbw4VEEom/CeE70sYmbAHmbgG7p495ktk514qSJdMQWGjegRKzoPMcnUXLcI4gCdDgTWmKIorY0ho2oFVU/bTx+07xfrjEAJUitcTW0ifpQouj6XmKHByjaeefbEPZze4tfpJE426RD+pPFZ4L1CrWIr1bPq/8CL0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=fB0MsEdR; 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="fB0MsEdR" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A52FFC19425; Mon, 27 Apr 2026 20:59:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777323575; bh=4fCdoQX9tOKa3DEv8CT8f6q/tReZla5dySYrHKOPds8=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=fB0MsEdRgoihroZKswclQKQK7DSaYaBeTbYgcnwk+cGwwMNHZs+Ewrbsx8gMZ3CyM QtJzJG7vGabw1+iCAwGf0eeEzwn4VwU6nVQ3BOASjmOtgG9H5rY8QhX2YWlZAfPVNo zoz0HYLK/I5mosk9uxs6yULiL2WCKuks9JvwOebp4t60hFYZEACArzvOGq1sLEAm6t H4DtPpdc96HIPXtY7h0zoyvunWqXabnlUPE25QE3718JB7KMtR/87czjxFFJIj5lo1 D6BQLhkgCE5rpeS8GUVhFAPr3DDqFGeq9eMkxXKmYNzBOJebAuAgqyooYpqY16Qyr5 Ag0QFqf0GI2fw== Message-ID: <97192ac3-643d-4393-87ef-53a9f3ddaf95@kernel.org> Date: Mon, 27 Apr 2026 22:59:24 +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: 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" Cc: linux-sh@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-mm@kvack.org References: <20260427-page_mapped-v1-0-e89c3592c74c@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: <20260427-page_mapped-v1-0-e89c3592c74c@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit 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. -- Cheers, David