From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=95.215.58.139 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1792558674; b=wbCltNYYodCIkoPjD3jxhZLeBAl+E7T8OA9tBCzo5n/v2Wg+au/Rumh4L9+uAsvY56M3 /h3LAkSfr6mxqLAxlQe5VOr0EZcxu8zZtWw5vacsn4FgmcBxo5cOTb/+ylw89qNvE/rUp CLuczh+CL4mKAVf2oxJL8coZoJoMsC5QcRa5QzVDKTH8L1rMELHJvYxvyq9aSShf89KW2 JnFi+JWOvWQ9qi7UXLRobz8h/+h5f2fDcqcSikWmCNhG/+emmb746YSy5rknafD3yzCKV 8WEopd+5aqzwy9h3pwbiZWDO72uNltdjZZTpHRevDnuKLijSe4NtvhlrvVjVchFbhJQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792558674; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:From:To:Cc:Subject:Date:Message-ID: X-Mailer:In-Reply-To:References:MIME-Version:Content-Type: Content-Transfer-Encoding; bh=zx+oBx+DrGbWNeI4VpjTvUMhvmqGs16Tkaf005DeV3I=; b=O9mzY8pjZFg25Jjxz0I7m0B5nzB2zTgoStInyDVcxTypENSlSNIjYD63JTAo4eP/P1RM xqxkg4z9P3ZpcbJAoao+8mubtKMjphGmep36fk8bpHQ0nITmGibJvqB/ARctBEhsX8sBW 9zB7b3v2Aep7HAc5AHjO7N1Z/Yv+jfsPYAsMgCpKSHRT3bgCttFRa1hQxx6N9tnXBFb8z Ni6veJUfXImbGEGaeYhL6aOE/nNMpP+fDUkazc6wUeaD0fUWZYbpofp0KL03eQOxd3msS JVY7qnkJ5Op4Qa6l0qh5UI2hf9BpE1M8fotn7qcHX3K7TT6sNEAe5q0ZuuEpBwtu5Hg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=P1nAFsAZ; arc=none smtp.remote-ip=95.215.58.139 Received: from mta1.migadu.com (out-139.mta1.migadu.com [95.215.58.139]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7453B606A31A for ; Wed, 21 Oct 2026 04:57:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 7453B606A31A Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=P1nAFsAZ X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=sjeGNUTRu2TxaiR+y3T0ejou+De0JFn1tmqrXPbKj/s=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1792558670; v=1; x=1793163470; b=P1nAFsAZzDdN1cB/IenFnLQPPipDFBuS9xym0lWq5mfYtRLAmQt3QeAFqd9UdI9Z5L9z2SEB NkcYKNd/A305qIJHE0prhUlfm8WKsSHDgxEauR4yWMbISsWDa+qtw2breNYExxYCEAtViGNp8eK VBrXq8Bz1w3n/fLR8eQeH2sQ= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 7971245a92a56791; Wed, 21 Oct 2026 04:57:50 +0000 X-Mizu-Trace-ID: 7971245a92a56791 X-Migadu-Flow: FLOW_OUT From: Lance Yang To: songmuchun@bytedance.com Cc: akpm@linux-foundation.org, david@kernel.org, osalvador@suse.de, maddy@linux.ibm.com, corbet@lwn.net, muchun.song@linux.dev, lance.yang@linux.dev, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, mpe@ellerman.id.au, npiggin@gmail.com, chleroy@kernel.org, ritesh.list@gmail.com, sshegde@linux.ibm.com, skhan@linuxfoundation.org, rdunlap@infradead.org, qi.zheng@linux.dev, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/4] mm/sparse-vmemmap: map shared vmemmap tail pages as read-only Date: Wed, 21 Oct 2026 12:57:44 +0800 Message-ID: <20261021045744.93554-1-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20261019090830.1917657-2-songmuchun@bytedance.com> References: <20261019090830.1917657-2-songmuchun@bytedance.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On Mon, Oct 19, 2026 at 05:08:27PM +0800, Muchun Song wrote: >Both early HugeTLB HVO and device DAX use the common vmemmap population >path for shared tail mappings. Map these pages read-only so that illegal >writes fault instead of corrupting metadata shared by multiple tail >pages. > >For early HugeTLB, this moves existing write protection into initial >population without changing the final mapping. Device DAX gains the same >protection. > >Signed-off-by: Muchun Song >--- > Documentation/mm/vmemmap_dedup.rst | 3 +-- > mm/sparse-vmemmap.c | 3 +++ > 2 files changed, 4 insertions(+), 2 deletions(-) > >diff --git a/Documentation/mm/vmemmap_dedup.rst b/Documentation/mm/vmemmap_dedup.rst >index 8c287ae3f86c..76f903975a40 100644 >--- a/Documentation/mm/vmemmap_dedup.rst >+++ b/Documentation/mm/vmemmap_dedup.rst >@@ -193,5 +193,4 @@ There's no remapping of vmemmap given that device-dax memory is not part of > System RAM ranges initialized at boot. Thus the tail page deduplication > happens at a later stage when we populate the sections. > >-Deduplicated tail pages are not mapped read-only. The mapping layout is the same >-as HugeTLB. >+The mapping layout is the same as HugeTLB. >diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c >index 40eba70c0048..ba0496daf4de 100644 >--- a/mm/sparse-vmemmap.c >+++ b/mm/sparse-vmemmap.c >@@ -295,6 +295,9 @@ static pte_t * __meminit vmemmap_pte_populate(pmd_t *pmd, unsigned long addr, in > return NULL; > > entry = pfn_pte(PHYS_PFN(__pa(p)), PAGE_KERNEL); >+ /* Map the shared tail page as read-only to catch illegal writes. */ >+ if (vmemmap_optimizable_pfn(pfn)) >+ entry = pte_wrprotect(entry); LLM pointed out that an AO MCE before bootmem gather could still reach TestSetPageHWPoison() on a shared tail, since the head isn't marked hugetlb yet. Wouldn't that trigger an Oops ... Anyway, I wouldn't expect to hit that during boot. Reviewed-by: Lance Yang [...] Cheers, Lance