From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 5A9BB3803C4 for ; Tue, 10 Feb 2026 15:09:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770736175; cv=none; b=WioPPw00glPM7ShSzJelt3aBENS/k2pDkn+8gwhxUPSM2zVlQUBoMAe51EQJuFVdqplmnH0EjA0qgueO0ZigzCYAPkJja1bA5YWA+2XQUulNvMRUUKzMhP0Yz0hn6/7/yVXNW0A6ZCtIAwZeBkusGiOXgoNm+3rU4uJgH+R/CoM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770736175; c=relaxed/simple; bh=s/009tO/uoAW8gW8CH7txHUInh05s9+ISLI8TUUR38M=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Joohj951O8Ig3gg1g2GEwbOGvRBQ61wYr5aZp+q8hYCRKop9h1vb1lFVruXzF4fAaD3YhtLCt1xaLORMhmji5OnhqVrgWwMGr5hBY+aymmzqn73Wn5bp1OS37SFgVlmwI+rJ4boPQa+dUHVBqRlAb8woW9j47d7g9KplbC05eeY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=VdoawcPU; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="VdoawcPU" Received: by smtp.kernel.org (Postfix) with ESMTPSA id ACA02C19421; Tue, 10 Feb 2026 15:09:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770736174; bh=s/009tO/uoAW8gW8CH7txHUInh05s9+ISLI8TUUR38M=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=VdoawcPU3pX+D8rF50VjcDAndYGaq86GorjJ9aukdRXku0zA3Fw6p2dOwqQtRNiSv tgVK7NwQMvx3J20AB/r8Q3AGl02aw+fUizk+J/c0haKUfWpBnffZ9goqRWMnI9fkGY P/JgUk3ev+ul4M6bvVbqWwu1W5D0T7/58XChisOa3QEcxa2sWJnYIbX4db2ilQ75xB EZBehxpuhgZ181BYTfo2FdPCtz43kPHHhxvF8fDRPlFenll9X6bMOr3+vbMslvLi7V Cq7F+fQ93cyTcBC+yxjG8aoLExRhaq6Z/aK5/q/x/Nw5F5UCptpkZHqBFiijoKDMkG 2idMLHv2Ujf7Q== Date: Tue, 10 Feb 2026 17:09:28 +0200 From: Mike Rapoport To: Michal Clapinski Cc: Evangelos Petrongonas , Pasha Tatashin , Pratyush Yadav , Alexander Graf , kexec@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton Subject: Re: [PATCH v2] kho: add support for deferred struct page init Message-ID: References: <20260210130418.297153-1-mclapinski@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260210130418.297153-1-mclapinski@google.com> Hi Michal, On Tue, Feb 10, 2026 at 02:04:18PM +0100, Michal Clapinski wrote: > 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. Please drop md-style markup, plain text is fine :) > Signed-off-by: Evangelos Petrongonas > Signed-off-by: Michal Clapinski > --- > 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=users/vpetrog/linux.git;a=shortlog;h=refs/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 > > menu "Live Update and Kexec HandOver" > - depends on !DEFERRED_STRUCT_PAGE_INIT > > 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_handover.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; > } > > +/* > + * With CONFIG_DEFERRED_STRUCT_PAGE_INIT, struct pages in higher memory regions > + * may not be initialized yet at the time KHO deserializes preserved memory. > + * KHO uses the struct page to store metadata and a later initialization would > + * overwrite it. > + * Ensure all the struct pages in the preservation are > + * initialized. deserialize_bitmap() marks the reservation as noinit to make > + * 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 = PHYS_PFN(phys); > + int nid = early_pfn_to_nid(pfn); Getting nid when CONFIG_DEFERRED_STRUCT_PAGE_INIT=n is a pure overhead because struct pages are initialized before KHO kho_mem_deserialize(). Other than that LGTM. > + > + for (int i = 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 order, > int sz = 1 << (order + PAGE_SHIFT); > phys_addr_t phys = > elm->phys_start + (bit << (order + PAGE_SHIFT)); > - struct page *page = phys_to_page(phys); > + struct page *page = kho_get_preserved_page(phys, order); > union kho_page_info info; > > memblock_reserve(phys, sz); > -- > 2.53.0.rc2.204.g2597b5adb4-goog > -- Sincerely yours, Mike.