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b=CsLTmwDYUQuPdEGJ2URh4YYrVQjku/PYtQd8szB9HFBHKuxNiHG8jlkrL7gi1baJv baOlP721yc+Gapvn+co/bsCE+vzOe7wj38uGpYqZPkxomRAwIz0bQTUhRLhTAuqqra dcAYfgKFIupV+om73sgPaweqXIGMwkg5fWtKJMpvY7FG1n04OkQOJYThS8OWkrXRF/ 6d+zCI/PEFFnvI3TBktpF/UQ7XAfs6aQrSu5o0XLNpvLlz/KIh0d4q4F8mng6kmC35 gHgYzeK4HV1Zw3Tpumbe8aupeoEBK6jboDtDlQeHq19XetZJxR/N2esfUJW+ShNiZf qTij8AvQ7COkA== Date: Thu, 3 Sep 2026 12:22:45 +0300 From: Mike Rapoport To: Xueyuan Chen Cc: akpm@linux-foundation.org, david@kernel.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, 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 Subject: Re: [PATCH v7 1/3] mm: make persistent huge zero folio read-only Message-ID: References: <20260901151818.3191443-1-xueyuan.chen21@gmail.com> <20260901151818.3191443-2-xueyuan.chen21@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260901151818.3191443-2-xueyuan.chen21@gmail.com> X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: AD6E6180003 X-Stat-Signature: ysixot88awssd53rgs4upduiays5qp3j X-HE-Tag: 1788427377-511503 X-HE-Meta: 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 /WJM43iy sayDaqbjewz0X1qXGFwl7c3gMRikUf+a8VyuAbjt1s9ydgxQub6L+9GHBqJDJ9AbKtdo4XWEUoL/Ar4nfMOnPwCr1MVmR4LZDx+LZksv95Dk5N5NpPxMVDjd3/KxKjSuZMOVfdJSbfABW41QtlCMYxH97SdDmFwx68f5zVtShESzkPOQyMT2knEW1l78gaGh2nZIZDE0C8SD6DhaQlrvECsAze9okx9YkgiJeJRioTqtnKhF1TPlQND+0CoIlo3009NsTqF+Ri+K8/e9dJuDpyWkkuxueoLriZrgY1kMMVc3g6jJLjMm+6/tU21HS52Tg09ifJvw5WcYD/OLwZE/wEMhWNONQiNiPpJiHb+Qsxp5rK6kqLVfZazR3UShL3G/DOO36l4xUirP+hD9F8Ez0++I6nA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Sep 01, 2026 at 11:18:16PM +0800, 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); Sorry, I don't remember if it was discussed previously, but why can't we use the existing set_memory_ro() here? > + > return 0; > } > > -- > 2.47.3 > -- Sincerely yours, Mike.