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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: Alexander Gordeev <agordeev@linux.ibm.com>
Reviewed-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
This commit is contained in:
Alexander Gordeev 2021-11-04 07:14:46 +01:00 committed by Heiko Carstens
parent 1194372db6
commit 4c88bb96e4
1 changed files with 30 additions and 11 deletions
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41
arch/s390/mm/pgalloc.c
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@ -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)
break;
fallthrough;
return;
break;
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);
}
/*