From nobody Thu Apr 2 14:14:43 2026 Received: from mail-ej1-f73.google.com (mail-ej1-f73.google.com [209.85.218.73]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1A05E27E074 for ; Tue, 10 Feb 2026 13:04:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.218.73 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770728678; cv=none; b=bMk0s7krYx+vQ3bOZMB5TI/d4yU0DU0HBUNUINFFz99iTyqv/cI+YohhNir4WjvN2SBDHLyks39xOpZz9AYEZ9EPaaFcJ18i3ZUh4gyXKZYlyuR6mqsbP9IuH0eRdHm9eUk716RwqbqfikHGZHW0MRigyRWCLQPYDlX/9jbzwOw= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770728678; c=relaxed/simple; bh=ZyPetRtoHDf9E4hM5QL/iWKbPK0swQYU5hpkFDZjagw=; h=Date:Mime-Version:Message-ID:Subject:From:To:Cc:Content-Type; b=LmR6wHJHxknF5TphcGxjltUE4jdbbwvzlQFsbljiiuIY/oiPqp9fYzFAEFZt9j1qXpqCcEHgS6AlSOEEZjhvA6O160WFDOz6HdV+Au2i3HFt40WJWTf1g0/FXbgySQ9BNGyhFwOOViJXpQHiE/jFNwadTMFsLweDlUPidPX3OHQ= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--mclapinski.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=1/Kw1SCV; arc=none smtp.client-ip=209.85.218.73 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--mclapinski.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="1/Kw1SCV" Received: by mail-ej1-f73.google.com with SMTP id a640c23a62f3a-b8704795d25so366632966b.2 for ; Tue, 10 Feb 2026 05:04:36 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1770728675; x=1771333475; darn=vger.kernel.org; h=cc:to:from:subject:message-id:mime-version:date:from:to:cc:subject :date:message-id:reply-to; bh=eH6JL7gkCCkK21U6qSqUgOiFfCqEIuZ4GNLMeFzGLJ0=; b=1/Kw1SCV1aa0AuFpH2q+I38yphvE1/ZbKMJNjLLwp9e8irsO6002IkyfTL7fnh1BH8 hTK2OV5JFKSK0prVla1Lu9Kbv15ZvKgoeTYR6GBN6W15LTnC1uuMylpOHYxOWm63wNWw SdXbD0H0Fi/RLIE8pl5EfJeiOx48DXtgcxhdZr+aU3slg8dcgCHuAA2prI7D4hzX9oE9 72lTM9oyYg5fMjaFXVFY8e8qyh303vYvuLMNhqvENoPvDZTAUzXpYqpjI17xgI9mkeFn 6emhICaWez8pv+xW5Qek1dV1/LyN0iGmwyVEmKbpuVqfN9glsvszEJpttukhu675nP4b RN5g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1770728675; x=1771333475; h=cc:to:from:subject:message-id:mime-version:date:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=eH6JL7gkCCkK21U6qSqUgOiFfCqEIuZ4GNLMeFzGLJ0=; b=OanD2UJYwkyjJZYX+AaTsoCg8erfW8pUfENHGPzxpvXHc5WN57KF9cza6dXeKFlzKS puDahBdjjKqYPQTeLX867SqbfF0VuQBIKQ13NMOejKOK/xhnMFDXjjLaXCpUOvbLKXkP CrtbZPHJiTJRw99D+IsfNV2dP0iVl0TkCybG8DcZZDCpuBeNI3dR/3RXqZG1R7Oxqec6 wrG26Nb1nKE7snoCm24wWrwehrT3vX+PWTAu6Rtaq2Ov9J8YcRHRkq3zWxd5iWpDAyM+ PV+HxhaZNDTDtJdh2yYVDH5UEw4kaNFGXV400paO8/iRt3Bxx0zjeCVn6bIQUTD8/1Z1 tywQ== X-Gm-Message-State: AOJu0YxPkNG+pTOhilowZX4qbBXusTycYT4Q0ldLEqFYPc319KWmMTLR z8OgOD07lGRRTkZw22oXXXAEx3lM1xVJaOdnqn2RkYmtAmJTH9pXfxUpCxIWYFmOx0bH9N6YWKC Ho4gWQmmAsOQ7iSP3KtbPhw== X-Received: from ejeo7.prod.google.com ([2002:a17:906:8c7:b0:b8d:7cde:ce4d]) (user=mclapinski job=prod-delivery.src-stubby-dispatcher) by 2002:a17:907:9810:b0:b73:2b08:ac70 with SMTP id a640c23a62f3a-b8edf33e476mr828942066b.49.1770728675354; Tue, 10 Feb 2026 05:04:35 -0800 (PST) Date: Tue, 10 Feb 2026 14:04:18 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 X-Mailer: git-send-email 2.53.0.rc2.204.g2597b5adb4-goog Message-ID: <20260210130418.297153-1-mclapinski@google.com> Subject: [PATCH v2] kho: add support for deferred struct page init From: Michal Clapinski To: Evangelos Petrongonas , Pasha Tatashin , Mike Rapoport , Pratyush Yadav , Alexander Graf , kexec@lists.infradead.org, linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Andrew Morton , Michal Clapinski 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. Signed-off-by: Evangelos Petrongonas Signed-off-by: Michal Clapinski Reviewed-by: Pratyush Yadav (Google) --- v2: updated a comment I think we can't initialize those struct pages in kho_restore_page. I encountered this stack: page_zone(start_page) __pageblock_pfn_to_page set_zone_contiguous page_alloc_init_late So, at the end of page_alloc_init_late struct pages are expected to be already initialized. set_zone_contiguous() looks at the first and last struct page of each pageblock in each populated zone to figure out if the zone is contiguous. If a kho page lands on a pageblock boundary, this will lead to access of an uninitialized struct page. There is also page_ext_init that invokes pfn_to_nid, which calls page_to_nid for each section-aligned page. There might be other places that do something similar. Therefore, it's a good idea to initialize all struct pages by the end of deferred struct page init. That's why I'm resending Evangelos's patch. I also tried to implement Pratyush's idea, i.e. iterate over zones, then get node from zone. I didn't notice any performance difference even with 8GB of kho. I repeated Evangelos's 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 --- kernel/liveupdate/Kconfig | 2 -- kernel/liveupdate/kexec_handover.c | 23 ++++++++++++++++++++++- 2 files changed, 22 insertions(+), 3 deletions(-) diff --git a/kernel/liveupdate/Kconfig b/kernel/liveupdate/Kconfig index 1a8513f16ef7..c13af38ba23a 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 b851b09a8e99..26bb45b25809 100644 --- a/kernel/liveupdate/kexec_handover.c +++ b/kernel/liveupdate/kexec_handover.c @@ -457,6 +457,27 @@ static int kho_mem_serialize(struct kho_out *kho_out) return err; } =20 +/* + * With CONFIG_DEFERRED_STRUCT_PAGE_INIT, struct pages in higher memory re= gions + * may not be initialized yet at the time KHO deserializes preserved memor= y. + * KHO uses the struct page to store metadata and a later initialization w= ould + * overwrite it. + * Ensure all the struct pages in the preservation are + * initialized. deserialize_bitmap() marks the reservation as noinit to ma= ke + * sure they don't get re-initialized later. + */ +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) { @@ -467,7 +488,7 @@ 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 2.53.0.rc2.204.g2597b5adb4-goog