Commit 4c88bb96 authored by Alexander Gordeev's avatar Alexander Gordeev Committed by Heiko Carstens
Browse files

s390/mm: check 2KB-fragment page on release 



When CONFIG_DEBUG_VM is defined check that pending remove
and tracking nibbles (bits 31-24 of the page refcount) are
cleared. Should the earlier stages of the page lifespan
have a race or logical error, such check could help in
exposing the issue.

Signed-off-by: default avatarAlexander Gordeev <agordeev@linux.ibm.com>
Reviewed-by: default avatarGerald Schaefer <gerald.schaefer@linux.ibm.com>
Signed-off-by: default avatarHeiko Carstens <hca@linux.ibm.com>
parent 1194372d

arch/s390/mm/pgalloc.c

+30 −11
Original line number Diff line number Diff line
@@ -311,10 +311,23 @@ unsigned long *page_table_alloc(struct mm_struct *mm) 
	return table;

}



static void page_table_release_check(struct page *page, void *table,

				     unsigned int half, unsigned int mask)

{

	char msg[128];



	if (!IS_ENABLED(CONFIG_DEBUG_VM) || !mask)

		return;

	snprintf(msg, sizeof(msg),

		 "Invalid pgtable %p release half 0x%02x mask 0x%02x",

		 table, half, mask);

	dump_page(page, msg);

}



void page_table_free(struct mm_struct *mm, unsigned long *table)

{

	unsigned int mask, bit, half;

	struct page *page;

	unsigned int bit, mask;



	page = virt_to_page(table);

	if (!mm_alloc_pgste(mm)) {
@@ -337,10 +350,14 @@ void page_table_free(struct mm_struct *mm, unsigned long *table) 
		mask >>= 24;

		if (mask != 0x00U)

			return;

		half = 0x01U << bit;

	} else {

		atomic_xor_bits(&page->_refcount, 0x03U << 24);

		half = 0x03U;

		mask = atomic_xor_bits(&page->_refcount, 0x03U << 24);

		mask >>= 24;

	}



	page_table_release_check(page, table, half, mask);

	pgtable_pte_page_dtor(page);

	__free_page(page);

}
@@ -380,28 +397,30 @@ void page_table_free_rcu(struct mmu_gather *tlb, unsigned long *table, 


void __tlb_remove_table(void *_table)

{

	unsigned int mask = (unsigned long) _table & 0x03U;

	unsigned int mask = (unsigned long) _table & 0x03U, half = mask;

	void *table = (void *)((unsigned long) _table ^ mask);

	struct page *page = virt_to_page(table);



	switch (mask) {

	switch (half) {

	case 0x00U:	/* pmd, pud, or p4d */

		free_pages((unsigned long) table, 2);

		break;

		return;

	case 0x01U:	/* lower 2K of a 4K page table */

	case 0x02U:	/* higher 2K of a 4K page table */

		mask = atomic_xor_bits(&page->_refcount, mask << (4 + 24));

		mask >>= 24;

		if (mask != 0x00U)

			return;

		break;

		fallthrough;

	case 0x03U:	/* 4K page table with pgstes */

		if (mask & 0x03U)

			atomic_xor_bits(&page->_refcount, 0x03U << 24);

		pgtable_pte_page_dtor(page);

		__free_page(page);

		mask = atomic_xor_bits(&page->_refcount, 0x03U << 24);

		mask >>= 24;

		break;

	}



	page_table_release_check(page, table, half, mask);

	pgtable_pte_page_dtor(page);

	__free_page(page);

}



/*