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 EBA9134B662 for ; Wed, 9 Sep 2026 15:18:22 +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=1788967105; cv=none; b=eLWGk4IZ/ehhtNel97lrdljdfVl42buS00ovdeY+x+NLsRryHbJYi1P+8b5tifnDVDKxxWi1/WF6m0CEwXKgpbA3/xj2DNh1WR3a2A/4J0a35F2SMPSTaG2H6cTG9GUl32wLTw+9qxwLKlrcSaRK95/ohf++a/HH2JPoqU7CBBs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788967105; c=relaxed/simple; bh=2QGqX14GqjgukkUyFQMnBgMEEa9XRkfRy9MzyNDOasE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=PmO4L//OHFYHOoiVclFZjBpRh0vY+cCIMiGhIr40UzEs/OOYGNCW3OytPDWysJy8EL/47WHQan8827KRb5rTZINO1rP+UnhaGj7pa5PMq8bzYb1KiZVngA5BYZVksDeavY1SI+4FxxQdmZ4DymR5uaHv5sfuqP0Vd3j71BaYKSY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=B/7HNL27; 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="B/7HNL27" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9F7151F00A3A; Wed, 9 Sep 2026 15:18:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788967102; bh=aaD1iPdHXSKMIWmNsAZlaxDbgZwjJL30YcYTVXTbOpI=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=B/7HNL27KzdYtSLenvs3BSAsGzCESsMj1zTYAn1O3A7hOZaYHx6vv7fAxQFh/9XlF umpFWbG7ESfKcSKaBH9RQH4Jtk7jle7SRHT8H/2hsfLhbOGgfmrGHEPGWuUAeD/AI+ Fdf1TsuqFzdEBbPLTrfA7OtbPK+QU/GRxuLLi1EaX35lZrhYtOhktDQ786wkQa1MYm PLmar6x3H1IC/SEFm2iWKXqamw/YLpo7TzpmgnD/xlu/oY3c5cJQskjplrtLNk+QSc mV4Z80C0uDtYHxdegJqKEct4ECUDs8YDYwLhISfXE7qdnCgyoH+spEaN1CQ13vahcT N0OtOBDb69WwQ== Message-ID: Date: Wed, 9 Sep 2026 17:18:11 +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 Cc: akpm@linux-foundation.org, 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> <1d5ac9d7-48ce-4fee-b893-f646bade4a86@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 9/8/26 16:48, Xueyuan Chen wrote: > On Tue, Sep 8, 2026 at 4:30 PM David Hildenbrand (Arm) wrote: >> >> 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? > > Hi David, > > We can move the check into set_direct_map_ro(). However, on x86, > set_direct_map_invalid_noflush() and set_direct_map_default_noflush() > also expect callers to exclude highmem pages. > > Would it make sense to make highmem a documented no-op for those > helpers as well, so the direct-map APIs handle it consistently? I think getting something consistent for now is the most important thing. :) -- Cheers, David