From nobody Sun Feb 8 23:25:44 2026 Received: from pdx-out-003.esa.us-west-2.outbound.mail-perimeter.amazon.com (pdx-out-003.esa.us-west-2.outbound.mail-perimeter.amazon.com [44.246.68.102]) (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 A389633A014 for ; Tue, 16 Dec 2025 08:49:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=44.246.68.102 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765874971; cv=none; b=M8d4g/07zYBYpzv2CeKRHwmdyD2ZiK/tgnHDyxEoJSG7H020pJaLrat0rd6/PDydmg8UlMLuwST9sHirECGSfzLHClr4u6GyoF9crtiRiKpHytAONTihVl5yAZCrj9TvEBuX0TGCb1uqaASoldV/sK6mPyoR80eh2UIj3NHTxVs= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765874971; c=relaxed/simple; bh=gAPlnZF6GXkP5MQoMPUSPDuDj/9sV+kjtW4slVD9w1w=; h=From:To:CC:Subject:Date:Message-ID:MIME-Version:Content-Type; b=NqjaNUyLFaebgFQDJ/WJv+88FBXNamOTQ+lRcTawbvr+QaGbOHQySSqpHlz2HOfghnmmIGtLdj5iezPikVMWVuVgUmo+Wsn6qKjbIcgKhAux0CTgzNUKqpt7G3Dpo8J9oW1lc6Eha9ieiqHhKUTasbp2KB8ixMhlmxUY1lTw9a4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amazon.de; spf=pass smtp.mailfrom=amazon.de; dkim=pass (2048-bit key) header.d=amazon.de header.i=@amazon.de header.b=IihFtJlW; arc=none smtp.client-ip=44.246.68.102 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amazon.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=amazon.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=amazon.de header.i=@amazon.de header.b="IihFtJlW" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.de; i=@amazon.de; q=dns/txt; s=amazoncorp2; t=1765874968; x=1797410968; h=from:to:cc:subject:date:message-id:mime-version: content-transfer-encoding; bh=t9GVMSE5QYBAq5Na9iKzheEhYI2L9XOqJpGx0SGLtLw=; b=IihFtJlWJR5Iy/Q1/IAau5v5x10/fjNk5Tv0QEyDFVAVHzSKqbUj7Q+1 IYRsuLCjJ4fqaZXxG6GIMxcJ1+n2/qBwU9qlSWQbB/sJMpE9bWgh/orYf MJXuTNv+/KbrQgKMygJgATfOHtuCDnGWCjNoZ4oMx91HK4RmOcChX6SI9 XxCZfaTKnoAkIs5xG3Hbx3fZaXe9wvVQ0EQRdzuT39YDZXplBKZJzKBG8 ReP14taCbR1a6XCdMPDDCh8kxjbIDXnT6fv1IHzgImvHTyaCoK2ZkDzsk e6qVjYc5L7so2YmbaaCB0C/YtiC7xUXdA7iAFez1Gy5MoywhRjdAw7qcn A==; X-CSE-ConnectionGUID: AB8P62TDTxCVBKRB7W9YBA== X-CSE-MsgGUID: giJnBZetQTewkmJV4jC3yw== X-IronPort-AV: E=Sophos;i="6.21,152,1763424000"; d="scan'208";a="9165717" Received: from ip-10-5-0-115.us-west-2.compute.internal (HELO smtpout.naws.us-west-2.prod.farcaster.email.amazon.dev) ([10.5.0.115]) by internal-pdx-out-003.esa.us-west-2.outbound.mail-perimeter.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 16 Dec 2025 08:49:25 +0000 Received: from EX19MTAUWA001.ant.amazon.com [205.251.233.236:20952] by smtpin.naws.us-west-2.prod.farcaster.email.amazon.dev [10.0.21.145:2525] with esmtp (Farcaster) id e256b7ba-6e38-433a-93d4-84c8c1e4bf24; Tue, 16 Dec 2025 08:49:25 +0000 (UTC) X-Farcaster-Flow-ID: e256b7ba-6e38-433a-93d4-84c8c1e4bf24 Received: from EX19D001UWA001.ant.amazon.com (10.13.138.214) by EX19MTAUWA001.ant.amazon.com (10.250.64.204) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.29; Tue, 16 Dec 2025 08:49:25 +0000 Received: from dev-dsk-epetron-1c-1d4d9719.eu-west-1.amazon.com (10.253.109.105) by EX19D001UWA001.ant.amazon.com (10.13.138.214) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.29; Tue, 16 Dec 2025 08:49:23 +0000 From: Evangelos Petrongonas To: Mike Rapoport CC: Evangelos Petrongonas , Pasha Tatashin , Pratyush Yadav , "Alexander Graf" , Andrew Morton , Jason Miu , , , , Subject: [PATCH] kho: add support for deferred struct page init Date: Tue, 16 Dec 2025 08:49:12 +0000 Message-ID: <20251216084913.86342-1-epetron@amazon.de> X-Mailer: git-send-email 2.47.3 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-ClientProxiedBy: EX19D042UWB002.ant.amazon.com (10.13.139.175) To EX19D001UWA001.ant.amazon.com (10.13.138.214) Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" When `CONFIG_DEFERRED_STRUCT_PAGE_INIT` is enabled, struct page initialization is deferred to parallel kthreads that run later in the boot process. During KHO restoration, `deserialize_bitmap()` writes metadata for each preserved memory region. However, if the struct page has not been initialized, this write targets uninitialized memory, potentially leading to errors like: ``` BUG: unable to handle page fault for address: ... ``` Fix this by introducing `kho_get_preserved_page()`, which ensures all struct pages in a preserved region are initialized by calling `init_deferred_page()` which is a no-op when deferred init is disabled or when the struct page is already initialized. Fixes: 8b66ed2c3f42 ("kho: mm: don't allow deferred struct page with KHO") Signed-off-by: Evangelos Petrongonas --- ### Notes @Jason, this patch should act as a temporary fix to make KHO play nice with deferred struct page init until you post your ideas about splitting "Physical Reservation" from "Metadata Restoration". ### Testing In order to test the fix, I modified the KHO selftest, to allocate more memory and do so from higher memory to trigger the incompatibility. The branch with those changes can be found in: https://git.infradead.org/?p=3Dusers/vpetrog/linux.git;a=3Dshortlog;h=3Dref= s/heads/kho-deferred-struct-page-init In future patches, we might want to enhance the selftest to cover this case as well. However, properly adopting the test for this is much more work than the actual fix, therefore it can be deferred to a follow-up series. In addition attempting to run the selftest for arm (without my changes) fails with: ``` ERROR:target/arm/internals.h:767:regime_is_user: code should not be reached Bail out! ERROR:target/arm/internals.h:767:regime_is_user: code should not = be reached ./tools/testing/selftests/kho/vmtest.sh: line 113: 61609 Aborted ``` I have not looked it up further, but can also do so as part of a selftest follow-up. kernel/liveupdate/Kconfig | 2 -- kernel/liveupdate/kexec_handover.c | 19 ++++++++++++++++++- 2 files changed, 18 insertions(+), 3 deletions(-) diff --git a/kernel/liveupdate/Kconfig b/kernel/liveupdate/Kconfig index d2aeaf13c3ac..9394a608f939 100644 --- a/kernel/liveupdate/Kconfig +++ b/kernel/liveupdate/Kconfig @@ -1,12 +1,10 @@ # SPDX-License-Identifier: GPL-2.0-only =20 menu "Live Update and Kexec HandOver" - depends on !DEFERRED_STRUCT_PAGE_INIT =20 config KEXEC_HANDOVER bool "kexec handover" depends on ARCH_SUPPORTS_KEXEC_HANDOVER && ARCH_SUPPORTS_KEXEC_FILE - depends on !DEFERRED_STRUCT_PAGE_INIT select MEMBLOCK_KHO_SCRATCH select KEXEC_FILE select LIBFDT diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_h= andover.c index 9dc51fab604f..78cfe71e6107 100644 --- a/kernel/liveupdate/kexec_handover.c +++ b/kernel/liveupdate/kexec_handover.c @@ -439,6 +439,23 @@ static int kho_mem_serialize(struct kho_out *kho_out) return err; } =20 +/* + * With CONFIG_DEFERRED_STRUCT_PAGE_INIT, struct pages in higher memory + * regions may not be initialized yet at the time KHO deserializes preserv= ed + * memory. This function ensures all struct pages in the region are initia= lized. + */ +static struct page *__init kho_get_preserved_page(phys_addr_t phys, + unsigned int order) +{ + unsigned long pfn =3D PHYS_PFN(phys); + int nid =3D early_pfn_to_nid(pfn); + + for (int i =3D 0; i < (1 << order); i++) + init_deferred_page(pfn + i, nid); + + return pfn_to_page(pfn); +} + static void __init deserialize_bitmap(unsigned int order, struct khoser_mem_bitmap_ptr *elm) { @@ -449,7 +466,7 @@ static void __init deserialize_bitmap(unsigned int orde= r, int sz =3D 1 << (order + PAGE_SHIFT); phys_addr_t phys =3D elm->phys_start + (bit << (order + PAGE_SHIFT)); - struct page *page =3D phys_to_page(phys); + struct page *page =3D kho_get_preserved_page(phys, order); union kho_page_info info; =20 memblock_reserve(phys, sz); --=20 2.43.0 Amazon Web Services Development Center Germany GmbH Tamara-Danz-Str. 13 10243 Berlin Geschaeftsfuehrung: Christof Hellmis, Andreas Stieger Eingetragen am Amtsgericht Charlottenburg unter HRB 257764 B Sitz: Berlin Ust-ID: DE 365 538 597