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

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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: a667300bd5 ("kho: add support for preserving vmalloc allocations")
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reported-by: Pratyush Yadav <pratyush@kernel.org>
Cc: Alexander Graf <graf@amazon.com>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Mike Rapoport (Microsoft)
2025-11-25 13:09:17 +02:00
committed by Andrew Morton
parent 4bc84cd539
commit 7b71205ae1
1 changed files with 12 additions and 8 deletions
Download Patch File Download Diff File Expand all files Collapse all files

20
kernel/liveupdate/kexec_handover.c
View File

@@ -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;
}