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b=Hbo8oTeRLq/G0/qNbB7YGWd3dqSCmtSDilBsD797FE8yTqU3sx0WcQ0oS9XbIIpUE A1GWb4UWvEa2lM04K4NCr3r7qRI9cmv98vwCQgZVTms9IFLwe+y25M2E08EtQ5kXvU TK/vUY9zjpNsqyq7VdV5gTZWHbI/+OiaQc22SSNijzPlesacMt+VEYZrtf5A9XAjj8 64ZUmYp1Uo1yret9r+Dq7qgLLV/WTAto0tXRshAdik+sxBzHCbBTvB711h3J8tuCnf qjZNADObhwdt7CptI8g+ytiqygIxaDnlT0aWUKMEA2VDySzXf4rLHFIODj+3H4tvZv xAjV+tyoF8VQg== Date: Wed, 4 Feb 2026 20:44:48 +0200 From: Mike Rapoport To: Evangelos Petrongonas Cc: Pasha Tatashin , Pratyush Yadav , Alexander Graf , Andrew Morton , Jason Miu , linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-mm@kvack.org, nh-open-source@amazon.com Subject: Re: [PATCH] kho: add support for deferred struct page init Message-ID: References: <20251216084913.86342-1-epetron@amazon.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251216084913.86342-1-epetron@amazon.de> X-Rspamd-Queue-Id: 902D5C000A X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: pr9up8jno7maunpn8dymyp9qeaaumcue X-HE-Tag: 1770230696-109607 X-HE-Meta: U2FsdGVkX1+YOz7D7ivkd9JpmJgwnib4jbxiCD3CQlXfnQAM6jkpsezSIY10QZ2WXLwcyE50Qb3ye9VYNOScicjI/Wdn3oaiqIwNCwIdiGB1prMP2z1NuBaUAkJnWtk17SfKyyBYWBE1xTOCOjFpO0M6z7ytVUyeYLh+QKwAAuZH+FO+12UpHLvJMedA36Bno9X4lE1uLW8FGskEq2saurU0CE0UJ4ERKSSGP+ZHc+2r8mIni3zmhfILG2tCFWml/sLmuq/EoQgvj/LOdivgHjqWv4uAMwLmKMmRD7AaB/oox8FyfOYs8ggU5vcXyVhrU1f1ziwAfrmhq8TGpTP4VAxiaRfCwF6ZRZ0kOrlS4sko59+xGjzs2adUtNBdGm6S+FA01EQ4vNvymeDY8mjwsnZoRf1WI0ncTvGVMthTdnf4P0wzLa3rtLDtlj1/rj6e644eZ4BOcFlb03yuXdfz80HRGMMikuN8o8vOl2YChOKROlLFDqcCMXB933WgjqOLHXCwq4rP+K0A1GfAGs6Fj9iPQEz4UvNi+Z/Pq/DONJ4uD82lGz/0PQv9RB5HgeAz2gzplH4Bw7QkpT/5Yvo4dqAKqQXJQOLTcDcqgrBFpSYjUZwOfTBQQ5XYMVgXev+xb8u/m4bGE9Oau9v7BoKSrrS8Tz0Muk5OmQDFrF1Cke9kQN9u3n5Tds9MKMU5dMI6VeN4VCxV0U44JgRgKHcrqKIdbGLPCIpFlLm9U0BToKOUYDSVNYrrm/MSu8GIgmI+S+iUH29nS/H3NDLTG4bnGiHbAsB/+RElYZXBGKR5db9rm9rNeHvBOfBHyfwD8eHitwaDplEY+OBAPHe8BcfYA07o0gFPGN2HhgRSel8TfNBkKUUHJUQtn9gPqAbw4gnvevVknpuP++cAJB1Sb55pcsWQyiVmZ7razXlwMJo6FJdddLqNCut5VkQ0F+aIZ2CgEukvsRZXnEsZU1RwSdM 0eHnxEaO U/YoKA8CLuTdbrZmMQVJWmDUdCOmqPsHcvtdpeiF3SfUGvV6ZVkVsF2GMZFNPHKzVOUL8IWkgx2Z7OpAxR50H5beF1JFpUFlKEYJpVDTo9bNnjpud6+D4PQPaDzBl8u9H19gqr4X9DJU78Ef85PGKikr4ELH1Z4S3Z/y/VdDt22YVtmgMIMaS1V1qIyfQ6kRYoz/lrG8x+yiDAxi1H5mv11dMGsAXE8bHaX4SRDaRzMvSQl7DL54+VOX7qFwhw6dfILxg29Ou0CA8/ME8HzLAd7QXapMQoSAmxDmjB4lnvaq6a4uaGeJzBj6M6g== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Evangelos, Are you planning to send a v2? On Tue, Dec 16, 2025 at 08:49:12AM +0000, Evangelos Petrongonas 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. > > 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=users/vpetrog/linux.git;a=shortlog;h=refs/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 > > 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 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; > } > > +/* > + * With CONFIG_DEFERRED_STRUCT_PAGE_INIT, struct pages in higher memory > + * regions may not be initialized yet at the time KHO deserializes preserved > + * memory. This function ensures all struct pages in the region are initialized. > + */ > +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); > + > + 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) > { > @@ -449,7 +466,7 @@ 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); > -- > 2.43.0 > > > > > 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 > -- Sincerely yours, Mike.