The current KHO page preservation APIs (e.g. kho_preserve_pages) assume that multi-page blocks are split into independent 4KB pages during restoration. This is incompatible with high-order non-compound pages, such as DMA buffers, which must be restored with tail pages having a zero reference count.
Introduce explicit preserve and restore APIs for unsplit pages, which preserve and restore a high-order page block as a single unit, applying a refcount of 1 to the head page while leaving tail pages at 0. Rename the existing internal helper to __kho_restore_page(). Signed-off-by: Pranjal Shrivastava <[email protected]> --- include/linux/kexec_handover.h | 10 ++++ kernel/liveupdate/kexec_handover.c | 86 ++++++++++++++++++++++++++++-- 2 files changed, 92 insertions(+), 4 deletions(-) diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h index 8968c56d2d73..6e2c75b16209 100644 --- a/include/linux/kexec_handover.h +++ b/include/linux/kexec_handover.h @@ -22,6 +22,8 @@ bool is_kho_boot(void); int kho_preserve_folio(struct folio *folio); void kho_unpreserve_folio(struct folio *folio); +int kho_preserve_page(struct page *page, unsigned int order); +void kho_unpreserve_page(struct page *page, unsigned int order); int kho_preserve_pages(struct page *page, unsigned long nr_pages); void kho_unpreserve_pages(struct page *page, unsigned long nr_pages); int kho_preserve_vmalloc(void *ptr, struct kho_vmalloc *preservation); @@ -30,6 +32,7 @@ void *kho_alloc_preserve(size_t size); void kho_unpreserve_free(void *mem); void kho_restore_free(void *mem); struct folio *kho_restore_folio(phys_addr_t phys); +struct page *kho_restore_page(phys_addr_t phys); struct page *kho_restore_pages(phys_addr_t phys, unsigned long nr_pages); void *kho_restore_vmalloc(const struct kho_vmalloc *preservation); int kho_add_subtree(const char *name, void *blob, size_t size); @@ -65,6 +68,13 @@ static inline int kho_preserve_pages(struct page *page, unsigned int nr_pages) static inline void kho_unpreserve_pages(struct page *page, unsigned int nr_pages) { } +static inline int kho_preserve_page(struct page *page, unsigned int order) +{ + return -EOPNOTSUPP; +} + +static inline void kho_unpreserve_page(struct page *page, unsigned int order) { } + static inline int kho_preserve_vmalloc(void *ptr, struct kho_vmalloc *preservation) { diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c index 07f6f453cd69..43ae3e2de5da 100644 --- a/kernel/liveupdate/kexec_handover.c +++ b/kernel/liveupdate/kexec_handover.c @@ -393,7 +393,7 @@ static void kho_init_folio(struct page *page, unsigned int order) prep_compound_page(page, order); } -static struct page *kho_restore_page(phys_addr_t phys, bool is_folio) +static struct page *__kho_restore_page(phys_addr_t phys, bool is_folio) { struct page *page = pfn_to_online_page(PHYS_PFN(phys)); unsigned long nr_pages; @@ -432,12 +432,44 @@ static struct page *kho_restore_page(phys_addr_t phys, bool is_folio) */ struct folio *kho_restore_folio(phys_addr_t phys) { - struct page *page = kho_restore_page(phys, true); + struct page *page = __kho_restore_page(phys, true); return page ? page_folio(page) : NULL; } EXPORT_SYMBOL_GPL(kho_restore_folio); +/** + * kho_restore_page - restore a higher-order unsplit page block. + * @phys: physical address of the first page. + * + * Restore a higher-order unsplit page block that was preserved with + * kho_preserve_page(). + * + * Return: the head page on success, NULL on failure. + */ +struct page *kho_restore_page(phys_addr_t phys) +{ + struct page *page = pfn_to_online_page(PHYS_PFN(phys)); + unsigned long nr_pages; + union kho_page_info info; + + if (!page) + return NULL; + + info.page_private = page->private; + if (WARN_ON_ONCE(info.magic != KHO_PAGE_MAGIC)) + return NULL; + + nr_pages = (1UL << info.order); + page->private = 0; + + kho_init_unsplit_pages(page, info.order); + adjust_managed_page_count(page, nr_pages); + + return page; +} +EXPORT_SYMBOL_GPL(kho_restore_page); + /** * kho_restore_pages - restore list of contiguous order 0 pages. * @phys: physical address of the first page. @@ -457,7 +489,7 @@ struct page *kho_restore_pages(phys_addr_t phys, unsigned long nr_pages) while (pfn < end_pfn) { const unsigned int order = min(count_trailing_zeros(pfn), ilog2(end_pfn - pfn)); - struct page *page = kho_restore_page(PFN_PHYS(pfn), false); + struct page *page = __kho_restore_page(PFN_PHYS(pfn), false); if (!page) return NULL; @@ -890,6 +922,51 @@ void kho_unpreserve_folio(struct folio *folio) } EXPORT_SYMBOL_GPL(kho_unpreserve_folio); +/** + * kho_preserve_page - preserve a higher-order "unsplit" page block. + * @page: head page of the block. + * @order: order of the allocation. + * + * Instructs KHO to preserve a higher-order contiguous allocation (like a DMA + * buffer) as a single unit. It must be restored using kho_restore_page() to + * ensure the tail pages are correctly initialized with a zero refcount. + * + * If a driver needs to split a block that has been preserved with this + * function, it must first unpreserve the block using kho_unpreserve_page(), + * perform the split, and then re-preserve the individual pages using + * kho_preserve_pages(). + * + * Return: 0 on success, error code on failure + */ +int kho_preserve_page(struct page *page, unsigned int order) +{ + struct kho_radix_tree *tree = &kho_out.radix_tree; + const unsigned long pfn = page_to_pfn(page); + + if (WARN_ON(kho_scratch_overlap(pfn << PAGE_SHIFT, PAGE_SIZE << order))) + return -EINVAL; + + return kho_radix_add_page(tree, pfn, order); +} +EXPORT_SYMBOL_GPL(kho_preserve_page); + +/** + * kho_unpreserve_page - unpreserve a higher-order "unsplit" page block. + * @page: head page of the block. + * @order: order of the allocation. + * + * Instructs KHO to unpreserve a high-order block that was preserved by + * kho_preserve_page() before. + */ +void kho_unpreserve_page(struct page *page, unsigned int order) +{ + struct kho_radix_tree *tree = &kho_out.radix_tree; + const unsigned long pfn = page_to_pfn(page); + + kho_radix_del_page(tree, pfn, order); +} +EXPORT_SYMBOL_GPL(kho_unpreserve_page); + static unsigned int __kho_preserve_pages_order(unsigned long start_pfn, unsigned long end_pfn) { @@ -927,7 +1004,8 @@ static void __kho_unpreserve(struct kho_radix_tree *tree, * @nr_pages: number of pages. * * Preserve a contiguous list of order 0 pages. Must be restored using - * kho_restore_pages() to ensure the pages are restored properly as order 0. + * kho_restore_pages() to ensure the pages are restored properly as order 0 + * with each page having a reference count of 1 (split). * * Return: 0 on success, error code on failure */ -- 2.55.0.141.g00534a21ce-goog
