From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 56AF543A80B for ; Tue, 8 Sep 2026 08:30:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788856207; cv=none; b=rJTLZREMDjPexpo7kFKqe9qCpOSYLKhu5VVp2MI8hKbnhMa4HrOH2Aig20OKt6FX3ParkOR7l0I6X8UcJ2Rp5Y595D5ykinutQGjBzQDgrWqI3UpiG/MpQyLBorNzN9h3XMvsRkYVvXzcDk3UQREeD2hUDXdyCxGTSMkMHU0mns= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788856207; c=relaxed/simple; bh=aOCoYIAHIxlFwQV4J+InIGSdig2bm9qzsd+cFa8uh4Y=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Snj5pC7/LKkDuJPXI945wWau1hZuC+HUr8tCkPMSiJk44qJpwLiK8dfIxhH66QKUdJk74eE05dy16ACN/ITLU7icFi29arD8lYNoGxH+XllsdSU/zhago4YbNUC0TgSHM32Kk3TtAjSvSLzkvnusJfa3+IsNgp2F18u8XZkdvgk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=LfMk3wkz; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="LfMk3wkz" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B861B1F00A3A; Tue, 8 Sep 2026 08:29:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788856205; bh=ebCInI9e4Od3AHhat/r530l+pPuLJ5UuOoklobhTgGY=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=LfMk3wkzpvMtWNa9uiopWPpLLfLC13UUn6mEqFqhG/qMNhTUxJTv7gWgiL7w95bRD 0vKcjlDAq/jahkdL2mFfijUfIk0dy98QCKqCYCoBiamLeocjj2qYqrxrBv7ARFcR5C Rxvjll3Oi27ywmi1n3bgfo8nr6Os4VRAiVCza9J/7bwfxXclMu+540O9RdZLegUk+b kRZQPL9CXB4lsxrAYrOFu5r6ACtrJAHouHzOogyfavu/f5tFWxhEAWPThHykKFonwd pH04EutZIU3bIOPIhD/5bI+sY9aOEhpBUDY+xHn3JTHWCT0ZZ093A872Pyd4rJMQRk 39FODpLeFY51A== Message-ID: <1d5ac9d7-48ce-4fee-b893-f646bade4a86@kernel.org> Date: Tue, 8 Sep 2026 10:29:55 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 1/3] mm: make persistent huge zero folio read-only To: Xueyuan Chen , akpm@linux-foundation.org Cc: ljs@kernel.org, usama.arif@linux.dev, ziy@nvidia.com, baolin.wang@linux.alibaba.com, liam@infradead.org, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, kas@kernel.org, rppt@kernel.org, catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com, linux-arm-kernel@lists.infradead.org, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, luto@kernel.org, peterz@infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260901151818.3191443-1-xueyuan.chen21@gmail.com> <20260901151818.3191443-2-xueyuan.chen21@gmail.com> 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: <20260901151818.3191443-2-xueyuan.chen21@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/1/26 17:18, Xueyuan Chen wrote: > The persistent huge zero folio is shared globally and should stay zero > after initialization. As Jann Horn pointed out [1], kernel bugs have > ended up writing to pages that were meant to be read-only, including in > security-sensitive cases. Making the folio read-only in the direct map > turns such writes into faults instead of silent zero-page corruption. > > Add a page-based helper consistent with the existing direct-map interfaces. > Handle TLB invalidation in the architecture implementation; unsupported > architectures retain their current behavior. > > Protect the folio after initialization. Skip highmem folios, which have no > permanent direct-map mapping. > > Inspired by Jann Horn's read-only zero page work [1] and follow-up > discussion [3] with Yang Shi. > > Link: https://lore.kernel.org/r/20260508-ro-zeropage-v1-1-9808abc20b49@google.com [1] > Link: https://lore.kernel.org/r/0e5b23a6-4895-454a-9dfa-6dc21adc2991@kernel.org [2] > Link: https://lore.kernel.org/r/CAHbLzkrXXe7r3n3jXgDKtwZhRqj=jDx9E6dLOULohnhBguvi9A@mail.gmail.com [3] > > Suggested-by: David Hildenbrand > Suggested-by: Usama Arif > Co-developed-by: Lance Yang > Signed-off-by: Lance Yang > Signed-off-by: Xueyuan Chen > --- > include/linux/set_memory.h | 17 +++++++++++++++++ > mm/huge_memory.c | 13 ++++++++++--- > 2 files changed, 27 insertions(+), 3 deletions(-) > > diff --git a/include/linux/set_memory.h b/include/linux/set_memory.h > index 3fe293cfed8c..ed9ce04b18a1 100644 > --- a/include/linux/set_memory.h > +++ b/include/linux/set_memory.h > @@ -54,6 +54,23 @@ static inline bool can_set_direct_map(void) > #endif > #endif /* CONFIG_ARCH_HAS_SET_DIRECT_MAP */ > > +#ifndef set_direct_map_ro > +/** > + * set_direct_map_ro - make a direct-map range read-only > + * @page: first page in the direct-map range > + * @nr: number of pages in the range > + * > + * Make the direct-map range starting at @page read-only and invalidate stale > + * writable translations before returning. > + * > + * Return: 0 on success, or a negative error code on failure. > + */ > +static inline int set_direct_map_ro(struct page *page, unsigned int nr) > +{ > + return 0; > +} > +#endif > + > #ifdef CONFIG_X86_64 > int set_mce_nospec(unsigned long pfn); > int clear_mce_nospec(unsigned long pfn); > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 54494c3fa983..742283b36d74 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -42,6 +42,7 @@ > #include > #include > #include > +#include > > #include > #include "internal.h" > @@ -291,10 +292,16 @@ static int __init huge_zero_init(void) > huge_zero_folio = alloc_huge_zero_folio(); > if (!huge_zero_folio) { > pr_warn("Allocating persistent huge zero folio failed\n"); > - } else { > - huge_zero_pfn = folio_pfn(huge_zero_folio); > - count_vm_event(THP_ZERO_PAGE_ALLOC); > + return 0; > } > + > + huge_zero_pfn = folio_pfn(huge_zero_folio); > + count_vm_event(THP_ZERO_PAGE_ALLOC); > + > + /* Highmem folios have no permanent direct-map mapping to protect. */ > + if (!folio_test_highmem(huge_zero_folio)) > + set_direct_map_ro(folio_page(huge_zero_folio, 0), HPAGE_PMD_NR); Assuming we keep the page-based approach, can't we just move the highmem test in there? -- Cheers, David