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Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wXdax-00000009JGM-0smk; Thu, 11 Jun 2026 11:29:11 +0000 Received: from sea.source.kernel.org ([2600:3c0a:e001:78e:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1wXdav-00000009JGF-0Kjk for linux-arm-kernel@lists.infradead.org; Thu, 11 Jun 2026 11:29:09 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id A28274066A; Thu, 11 Jun 2026 11:29:08 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B262A1F00893; Thu, 11 Jun 2026 11:29:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781177348; bh=1iXM+Lu7Us3RNKuTfxaVjOprYbkGH/NiJNcNKN4u9gM=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Y2zvRFMPXCvDIcnpv5C3TWA0r9mNn5coUfJtmV6ljqcuK7N5nJKKmxsBN+OE0jD7W a5HIlP+JikfA6mdizyZuh8fhKRMf6pywf60Iv2BIh9uENPDEEW8SLQWlp7VlDKLWeC EHPA10EYcoOoHwVLpeiXhNJ0mh+0S0ClwOCGOPnXR4OsWBW9PI2uMhr0u4Vn41Lzjs 9rDWHWcZrZd9ykx0uG3vwMvX8FfcYTHiooLJLDBQYAwXH8Y/KnvwyyMC7XGKKkvXGj 5bV2xIwLaVyWwJhHSBa5DltR9Tfm37gOpA52dsMGrUTXhZIiILbJlu4w+UzJfyGPRY mYJCjahLyRG0g== Message-ID: <8c36a91d-288f-4ffb-b2ec-41e3ef789d72@kernel.org> Date: Thu, 11 Jun 2026 13:28:58 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v2 1/3] mm/huge_memory: make persistent huge zero folio read-only To: Lance Yang , akpm@linux-foundation.org Cc: xueyuan.chen21@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, x86@kernel.org, catalin.marinas@arm.com, will@kernel.org, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, hpa@zytor.com, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, yang@os.amperecomputing.com, jannh@google.com, dave.hansen@intel.com References: <20260609124549.aff7e774603c4af188009408@linux-foundation.org> <20260610021508.46000-1-lance.yang@linux.dev> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-BeenThere: linux-arm-kernel@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-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 6/10/26 04:15, Lance Yang wrote: > > On Tue, Jun 09, 2026 at 12:45:49PM -0700, Andrew Morton wrote: >> On Tue, 9 Jun 2026 22:37:59 +0800 Xueyuan Chen wrote: >> >>> The huge zero folio is shared globally, and its contents should never >>> change after initialization. As Jann Horn pointed out[1], the kernel has >>> had bugs, including security bugs, where read-only pages were later written >>> to. If the persistent huge zero folio is read-only in the direct map, such >>> writes fault instead of silently corrupting the shared zero contents. >>> >>> Add arch_make_pages_readonly() so mm code can request read-only direct-map >>> protection for a page range. Direct-map protection is >>> architecture-specific, so the generic weak implementation does nothing. >>> >>> This was inspired by Jann Horn's read-only zero page work[1] and follow-up >>> discussion[2] with Yang Shi. >>> >>> [1] https://lore.kernel.org/linux-mm/20260508-ro-zeropage-v1-1-9808abc20b49@google.com/ >>> [2] https://lore.kernel.org/linux-mm/CAHbLzkrXXe7r3n3jXgDKtwZhRqj=jDx9E6dLOULohnhBguvi9A@mail.gmail.com/ >>> >>> ... >>> >>> --- a/mm/huge_memory.c >>> +++ b/mm/huge_memory.c >>> @@ -308,6 +308,11 @@ static unsigned long shrink_huge_zero_folio_scan(struct shrinker *shrink, >>> return 0; >>> } >>> >>> +bool __weak arch_make_pages_readonly(struct page *page, int nr_pages) >>> +{ >>> + return false; >>> +} >>> + >>> static struct shrinker *huge_zero_folio_shrinker; >>> >>> #ifdef CONFIG_SYSFS >>> @@ -982,8 +987,14 @@ static int __init thp_shrinker_init(void) >>> * that get_huge_zero_folio() will most likely not fail as >>> * thp_shrinker_init() is invoked early on during boot. >>> */ >>> - if (!get_huge_zero_folio()) >>> + if (!get_huge_zero_folio()) { >>> pr_warn("Allocating persistent huge zero folio failed\n"); >>> + return 0; >>> + } >>> + >>> + arch_make_pages_readonly(folio_page(huge_zero_folio, 0), >>> + HPAGE_PMD_NR); >> >> Can it simply pass the folio? > > Right, this came from the RFC v1 discussion[1]. David preferred a page- > range helper for possible future non-folio callers, not something folio- > only. > > Of course, we could also add a folio wrapper on top of that if needed :) Best to document that as part of the patch description: we don't really expect to have a lot of read-only folios in the near future (zero page is rather special; maybe it won't even be a folio in the future). -- Cheers, David