From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 45B7ECAC592 for ; Mon, 22 Sep 2025 17:59:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=X+NpTFRiqIAeX32lj/YJRRr02h3IMluyoifxGje7HdY=; b=1WTNHV2ER+a92mA9RIacLEmfQn QBKsjuUErIGR0xyWcyVP+qBkH2zhzo32LTu8KkCIfHAOrdRx10rRCvSn1poQa3S1QpijR7vdsIQ44 N/q9MtE6OFCDFlqFK26eUfDLswa6klNd68e5UZbBOkapKsli8Mq0mJEyYL68PfFtpmcvWxU1/IyeH eWRJkPovOe1NDKxyspZtrxmXgvOhwH9es3i37GrWhcxUwSmbI6wHPnRITdTHUSRSeLwmi1RMUAe5+ b6ROydIZVF4nzkVgLImLSVhVlcuU+8FlW072cnc9ORpj7iwxb1WyQyodKWeqmig34kvmqrtSA3EEg H5B71jlA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1v0kog-0000000BC8n-301q; Mon, 22 Sep 2025 17:59:10 +0000 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1v0kod-0000000BC7r-3fiJ for linux-mediatek@lists.infradead.org; Mon, 22 Sep 2025 17:59:09 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1758563946; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=X+NpTFRiqIAeX32lj/YJRRr02h3IMluyoifxGje7HdY=; b=N64cQPf23OMOKn8TGNdXivCw5IxXdU+/0DpoI6atO/EuAOX/IzzQVVa+2tecxAhUexQr+H 2vvm/pLkhVPR3uKa3BQ8sB4sUaRNcxibWiDxZOMzN+v9SCMvfFVUgfOqVdv7uxIVcjMhZF mefGu7QTh5oPip1a8hkIP9nhszRqWAY= Received: from mail-wm1-f70.google.com (mail-wm1-f70.google.com [209.85.128.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-589-qXVjIF28M4SKvYv9sOwFEQ-1; Mon, 22 Sep 2025 13:59:04 -0400 X-MC-Unique: qXVjIF28M4SKvYv9sOwFEQ-1 X-Mimecast-MFC-AGG-ID: qXVjIF28M4SKvYv9sOwFEQ_1758563944 Received: by mail-wm1-f70.google.com with SMTP id 5b1f17b1804b1-45f2b0eba08so33537735e9.3 for ; Mon, 22 Sep 2025 10:59:04 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1758563944; x=1759168744; h=content-transfer-encoding:in-reply-to:autocrypt:content-language :from:references:cc:to:subject:user-agent:mime-version:date :message-id:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=X+NpTFRiqIAeX32lj/YJRRr02h3IMluyoifxGje7HdY=; b=g/R/84oJfYcjrT88cB7lxJlN7+a4qSu41xw4Ge+ooionyTzEGK2IZQsxOhzynd65+K UobY9qOZBKtXHz2V6Y9CH9Ezr7Mt1gZN7trcAZ3vb6zT8NR93sn8WGU4rsxR2uA+UIFl dPWu2eTU87tTvtEmZ+ejsP+ZZOPuBjkMEhCu1y2haNRHfj3EXEW/7h8XCiFzbO3JYGXk jl0h4iWk+hSoQzqd2tlSHXyf66Hpkb08ks9IlcA2wpB7nL1pl4Th9oJPWf1VxY5zZwzP jTbCuZoxW98ichB/rFK9fhMoAp80zPxA66OpBBUN487T9cqGRGueO4w9SE5lrKFQQNml w1kg== X-Forwarded-Encrypted: i=1; AJvYcCVrMUDxapyRhVJQdZpUqoY3B2xNmZfa8lpuqLrT897371QFX4hMlVyw6j56klbxlzVeZk1TYykuQHhRHnuxZQ==@lists.infradead.org X-Gm-Message-State: AOJu0YwWRdsjtSBcVXLEf9Anvng47Kvwi+E8kq07An1Gc10vs6FXh/xC W6477Ncc9amSVp/EMRU++FjTSy+vbvxmgqveiDRki0tcoMS+rRiri9N9XL5em+0DzXqhisiKEnK +GJ0BXSuVpIm6ERXZCOt+Ezu3MWW9aKYBbMVZHdvQrV5fSEZ6QHBaBJsssz3s2/yMRmBpCCNQMg == X-Gm-Gg: ASbGnctu7iBoBkQdPOTbnSHp87upBMAKWaA+In9l3lZ0x7e4ujeFqAWJXtxHNEq4xK3 2cfu7NWkblrKgXak0TtHQtPTz4fC1tS164+DnTU/UGz93bNzCwfe7tMalCHiWWWvzk4ogqkPc0K HMvvJKLRautzCZcsOmg7d5pE/Fhoq4dLeL636owkhvmory3L6WCbAuNj6RylFjKEfc4DTjdELAA da8Hi/77TXBhe5p2JMbK0zzRUvHeF8+yH1Lb0ctLn3eYWaMs2GUXczKYUGpJ3n6u4BHpRV7WzhP pbf8mfmBWXAi6Y1/4goHMQ+7i4kU+i1ykAehFtv+906jXMLJsBdPwIhQmIJGb6SbHhvpsSQANKc tFcjuBXpQs1LSoJaFzwWxO0Ma34OYYrpspzUuI4h84YDd8JjniZ3MoJ7sIrwFA8s= X-Received: by 2002:a05:600c:468c:b0:46d:4f41:3704 with SMTP id 5b1f17b1804b1-46d4f41384dmr40724495e9.24.1758563943622; Mon, 22 Sep 2025 10:59:03 -0700 (PDT) X-Google-Smtp-Source: AGHT+IEoE/UaKLNkRz3YUEvL7yXGK4SAbmQlqVmH48OgbeeBRyoglBEIuVbqUV5YzWqsII28Z7eKwA== X-Received: by 2002:a05:600c:468c:b0:46d:4f41:3704 with SMTP id 5b1f17b1804b1-46d4f41384dmr40724115e9.24.1758563943097; Mon, 22 Sep 2025 10:59:03 -0700 (PDT) Received: from ?IPV6:2003:d8:2f2a:e200:f98f:8d71:83f:f88? (p200300d82f2ae200f98f8d71083f0f88.dip0.t-ipconnect.de. [2003:d8:2f2a:e200:f98f:8d71:83f:f88]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-461383b7b9csm253669505e9.2.2025.09.22.10.59.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 22 Sep 2025 10:59:02 -0700 (PDT) Message-ID: Date: Mon, 22 Sep 2025 19:59:00 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/1] mm/thp: fix MTE tag mismatch when replacing zero-filled subpages To: Catalin Marinas , Lance Yang Cc: akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, usamaarif642@gmail.com, yuzhao@google.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, baohua@kernel.org, voidice@gmail.com, Liam.Howlett@oracle.com, cerasuolodomenico@gmail.com, hannes@cmpxchg.org, kaleshsingh@google.com, npache@redhat.com, riel@surriel.com, roman.gushchin@linux.dev, rppt@kernel.org, ryan.roberts@arm.com, dev.jain@arm.com, ryncsn@gmail.com, shakeel.butt@linux.dev, surenb@google.com, hughd@google.com, willy@infradead.org, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, qun-wei.lin@mediatek.com, Andrew.Yang@mediatek.com, casper.li@mediatek.com, chinwen.chang@mediatek.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mediatek@lists.infradead.org, linux-mm@kvack.org, ioworker0@gmail.com, stable@vger.kernel.org References: <20250922021458.68123-1-lance.yang@linux.dev> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+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: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: Rxglt63VWWqZ3lY_qEDeub0NIfSaIkpWR8AoWK9Yauw_1758563944 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250922_105907_989506_70672B5D X-CRM114-Status: GOOD ( 23.33 ) X-BeenThere: linux-mediatek@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-mediatek" Errors-To: linux-mediatek-bounces+linux-mediatek=archiver.kernel.org@lists.infradead.org On 22.09.25 19:24, Catalin Marinas wrote: > On Mon, Sep 22, 2025 at 10:14:58AM +0800, Lance Yang wrote: >> From: Lance Yang >> >> When both THP and MTE are enabled, splitting a THP and replacing its >> zero-filled subpages with the shared zeropage can cause MTE tag mismatch >> faults in userspace. >> >> Remapping zero-filled subpages to the shared zeropage is unsafe, as the >> zeropage has a fixed tag of zero, which may not match the tag expected by >> the userspace pointer. >> >> KSM already avoids this problem by using memcmp_pages(), which on arm64 >> intentionally reports MTE-tagged pages as non-identical to prevent unsafe >> merging. >> >> As suggested by David[1], this patch adopts the same pattern, replacing the >> memchr_inv() byte-level check with a call to pages_identical(). This >> leverages existing architecture-specific logic to determine if a page is >> truly identical to the shared zeropage. >> >> Having both the THP shrinker and KSM rely on pages_identical() makes the >> design more future-proof, IMO. Instead of handling quirks in generic code, >> we just let the architecture decide what makes two pages identical. >> >> [1] https://lore.kernel.org/all/ca2106a3-4bb2-4457-81af-301fd99fbef4@redhat.com >> >> Cc: >> Reported-by: Qun-wei Lin >> Closes: https://lore.kernel.org/all/a7944523fcc3634607691c35311a5d59d1a3f8d4.camel@mediatek.com >> Fixes: b1f202060afe ("mm: remap unused subpages to shared zeropage when splitting isolated thp") >> Suggested-by: David Hildenbrand >> Signed-off-by: Lance Yang > > Functionally, the patch looks fine, both with and without MTE. > > Reviewed-by: Catalin Marinas > >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index 32e0ec2dde36..28d4b02a1aa5 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -4104,29 +4104,20 @@ static unsigned long deferred_split_count(struct shrinker *shrink, >> static bool thp_underused(struct folio *folio) >> { >> int num_zero_pages = 0, num_filled_pages = 0; >> - void *kaddr; >> int i; >> >> for (i = 0; i < folio_nr_pages(folio); i++) { >> - kaddr = kmap_local_folio(folio, i * PAGE_SIZE); >> - if (!memchr_inv(kaddr, 0, PAGE_SIZE)) { >> - num_zero_pages++; >> - if (num_zero_pages > khugepaged_max_ptes_none) { >> - kunmap_local(kaddr); >> + if (pages_identical(folio_page(folio, i), ZERO_PAGE(0))) { >> + if (++num_zero_pages > khugepaged_max_ptes_none) >> return true; > > I wonder what the overhead of doing a memcmp() vs memchr_inv() is. The > former will need to read from two places. If it's noticeable, it would > affect architectures that don't have an MTE equivalent. > > Alternatively we could introduce something like folio_has_metadata() > which on arm64 simply checks PG_mte_tagged. We discussed something similar in the other thread (I suggested page_is_mergable()). I'd prefer to use pages_identical() for now, so we have the same logic here and in ksm code. (this patch here almost looks like a cleanup :) ) If this becomes a problem, what we could do is in pages_identical() would be simply doing the memchr_inv() in case is_zero_pfn(). KSM might benefit from that as well when merging with the shared zeropage through try_to_merge_with_zero_page(). -- Cheers David / dhildenb