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