Commit 7b71205a authored by Mike Rapoport (Microsoft)'s avatar Mike Rapoport (Microsoft) Committed by Andrew Morton
Browse files

kho: fix restoring of contiguous ranges of order-0 pages 

When contiguous ranges of order-0 pages are restored, kho_restore_page()
calls prep_compound_page() with the first page in the range and order as
parameters and then kho_restore_pages() calls split_page() to make sure
all pages in the range are order-0.

However, since split_page() is not intended to split compound pages and
with VM_DEBUG enabled it will trigger a VM_BUG_ON_PAGE().

Update kho_restore_page() so that it will use prep_compound_page() when it
restores a folio and make sure it properly sets page count for both large
folios and ranges of order-0 pages.

Link: https://lkml.kernel.org/r/20251125110917.843744-3-rppt@kernel.org


Fixes: a667300b ("kho: add support for preserving vmalloc allocations")
Signed-off-by: default avatarMike Rapoport (Microsoft) <rppt@kernel.org>
Reported-by: default avatarPratyush Yadav <pratyush@kernel.org>
Cc: Alexander Graf <graf@amazon.com>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 4bc84cd5

kernel/liveupdate/kexec_handover.c

+12 −8
Original line number Diff line number Diff line
@@ -219,11 +219,11 @@ static int __kho_preserve_order(struct kho_mem_track *track, unsigned long pfn, 
	return 0;

}



static struct page *kho_restore_page(phys_addr_t phys)

static struct page *kho_restore_page(phys_addr_t phys, bool is_folio)

{

	struct page *page = pfn_to_online_page(PHYS_PFN(phys));

	unsigned int nr_pages, ref_cnt;

	union kho_page_info info;

	unsigned int nr_pages;



	if (!page)

		return NULL;
@@ -243,11 +243,16 @@ static struct page *kho_restore_page(phys_addr_t phys) 
	/* Head page gets refcount of 1. */

	set_page_count(page, 1);



	/* For higher order folios, tail pages get a page count of zero. */

	/*

	 * For higher order folios, tail pages get a page count of zero.

	 * For physically contiguous order-0 pages every pages gets a page

	 * count of 1

	 */

	ref_cnt = is_folio ? 0 : 1;

	for (unsigned int i = 1; i < nr_pages; i++)

		set_page_count(page + i, 0);

		set_page_count(page + i, ref_cnt);



	if (info.order > 0)

	if (is_folio && info.order)

		prep_compound_page(page, info.order);



	adjust_managed_page_count(page, nr_pages);
@@ -262,7 +267,7 @@ static struct page *kho_restore_page(phys_addr_t phys) 
 */

struct folio *kho_restore_folio(phys_addr_t phys)

{

	struct page *page = kho_restore_page(phys);

	struct page *page = kho_restore_page(phys, true);



	return page ? page_folio(page) : NULL;

}
@@ -287,11 +292,10 @@ struct page *kho_restore_pages(phys_addr_t phys, unsigned int 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));

		struct page *page = kho_restore_page(PFN_PHYS(pfn), false);



		if (!page)

			return NULL;

		split_page(page, order);

		pfn += 1 << order;

	}