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s390/vmem: Support 2G page splitting for KASAN shadow freeing

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Export split_pud_page() so it can be used from the vmem code and teach
modify_pud_table() to split PUD-sized mappings when only a subrange
needs to be removed.

If the range to be removed covers a full PUD-sized mapping, keep the
existing behavior: clear the PUD entry and free the backing large page
(for non-direct mappings). Otherwise, split the PUD-mapped page into
PMD mappings and let the walker handle the smaller ranges.

This is needed for KASAN early shadow removal support: memory hotplug
freeing the KASAN early shadow is the only expected caller that will
try to free 2G PUD-mapped regions of non-direct mappings.

Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
This commit is contained in:
Vasily Gorbik
2025-11-28 23:01:05 +01:00
committed by Heiko Carstens
parent 1442bb87b8
commit 6a35d02fec
3 changed files with 8 additions and 2 deletions
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2
arch/s390/include/asm/page.h
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@@ -166,6 +166,8 @@ static inline int page_reset_referenced(unsigned long addr)
return CC_TRANSFORM(cc);
}
int split_pud_page(pud_t *pudp, unsigned long addr);
/* Bits int the storage key */
#define _PAGE_CHANGED 0x02 /* HW changed bit */
#define _PAGE_REFERENCED 0x04 /* HW referenced bit */