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 <[email protected]> > Signed-off-by: Michal Clapinski <[email protected]> > --- > 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.
