The KHO restoration logic currently forces a refcount of 1 on every page of a multi-page block. While that is correct for split pages, it violates the expectations of the buddy allocator for high-order non-compound pages allocated by kernel user (like the DMA allocator), where tail pages are expected to have a refcount of 0.
Update the restoration path to respect the preserved page type stored in the page->private metadata. For KHO_PAGE_CONTIG blocks, only the head page is given a reference count of 1. For KHO_PAGE_SPLIT blocks, every page is given a reference count of 1. Signed-off-by: Pranjal Shrivastava <[email protected]> --- kernel/liveupdate/kexec_handover.c | 35 +++++++++++++++++------------- 1 file changed, 20 insertions(+), 15 deletions(-) diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c index d6e81f72fe5d..f6ca5e24c740 100644 --- a/kernel/liveupdate/kexec_handover.c +++ b/kernel/liveupdate/kexec_handover.c @@ -375,11 +375,18 @@ int kho_radix_walk_tree(struct kho_radix_tree *tree, } EXPORT_SYMBOL_GPL(kho_radix_walk_tree); -/* For physically contiguous 0-order pages. */ -static void kho_init_pages(struct page *page, unsigned long nr_pages) +/* For physically contiguous pages. */ +static void kho_restore_refcounts(struct page *page, unsigned long nr_pages, + enum kho_page_type type) { - for (unsigned long i = 0; i < nr_pages; i++) { - set_page_count(page + i, 1); + /* Head page always gets refcount of 1. */ + set_page_count(page, 1); + clear_page_tag_ref(page); + + for (unsigned long i = 1; i < nr_pages; i++) { + unsigned int count = (type == KHO_PAGE_SPLIT) ? 1 : 0; + + set_page_count(page + i, count); /* Clear each page's codetag to avoid accounting mismatch. */ clear_page_tag_ref(page + i); } @@ -387,16 +394,7 @@ static void kho_init_pages(struct page *page, unsigned long nr_pages) static void kho_init_folio(struct page *page, unsigned int order) { - unsigned long nr_pages = (1 << order); - - /* Head page gets refcount of 1. */ - set_page_count(page, 1); - /* Clear head page's codetag to avoid accounting mismatch. */ - clear_page_tag_ref(page); - - /* For higher order folios, tail pages get a page count of zero. */ - for (unsigned long i = 1; i < nr_pages; i++) - set_page_count(page + i, 0); + kho_restore_refcounts(page, 1 << order, KHO_PAGE_CONTIG); if (order > 0) prep_compound_page(page, order); @@ -421,13 +419,20 @@ static struct page *kho_restore_page(phys_addr_t phys, bool is_folio) return NULL; nr_pages = (1 << info.order); + /* + * If we want to restore a folio, but the memory was split in the + * previous kernel, something is wrong. + */ + if (WARN_ON_ONCE(is_folio && info.type == KHO_PAGE_SPLIT)) + return NULL; + /* Clear private to make sure later restores on this page error out. */ page->private = 0; if (is_folio) kho_init_folio(page, info.order); else - kho_init_pages(page, nr_pages); + kho_restore_refcounts(page, nr_pages, info.type); adjust_managed_page_count(page, nr_pages); return page; -- 2.55.0.rc0.799.gd6f94ed593-goog
