[PATCH mm-unstable v1 01/26] mm/debug_vm_pgtable: more pte_swp_exclusive() sanity checks

David Hildenbrand
2023-01-13T17:10:01Z

We want to implement __HAVE_ARCH_PTE_SWP_EXCLUSIVE on all architectures.
Let's extend our sanity checks, especially testing that our PTE bit
does not affect:
* is_swap_pte() -> pte_present() and pte_none()
* the swap entry + type
* pte_swp_soft_dirty()

Especially, the pfn_pte() is dodgy when the swap PTE layout differs
heavily from ordinary PTEs. Let's properly construct a swap PTE from
swap type+offset.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
mm/debug_vm_pgtable.c | 23 ++++++++++++++++++++++-
1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
index bb3328f46126..a0730beffd78 100644
--- a/mm/debug_vm_pgtable.c
+++ b/mm/debug_vm_pgtable.c
@@ -811,13 +811,34 @@ static void __init pmd_swap_soft_dirty_tests(struct pgtable_debug_args *args) {
static void __init pte_swap_exclusive_tests(struct pgtable_debug_args *args)
{
#ifdef __HAVE_ARCH_PTE_SWP_EXCLUSIVE
- pte_t pte = pfn_pte(args->fixed_pte_pfn, args->page_prot);
+ unsigned long max_swapfile_size = generic_max_swapfile_size();
+ swp_entry_t entry, entry2;
+ pte_t pte;

pr_debug("Validating PTE swap exclusive\n");
+
+ /* Create a swp entry with all possible bits set */
+ entry = swp_entry((1 << MAX_SWAPFILES_SHIFT) - 1,
+ max_swapfile_size - 1);
+
+ pte = swp_entry_to_pte(entry);
+ WARN_ON(pte_swp_exclusive(pte));
+ WARN_ON(!is_swap_pte(pte));
+ entry2 = pte_to_swp_entry(pte);
+ WARN_ON(memcmp(&entry, &entry2, sizeof(entry)));
+
pte = pte_swp_mkexclusive(pte);
WARN_ON(!pte_swp_exclusive(pte));
+ WARN_ON(!is_swap_pte(pte));
+ WARN_ON(pte_swp_soft_dirty(pte));
+ entry2 = pte_to_swp_entry(pte);
+ WARN_ON(memcmp(&entry, &entry2, sizeof(entry)));
+
pte = pte_swp_clear_exclusive(pte);
WARN_ON(pte_swp_exclusive(pte));
+ WARN_ON(!is_swap_pte(pte));
+ entry2 = pte_to_swp_entry(pte);
+ WARN_ON(memcmp(&entry, &entry2, sizeof(entry)));
#endif /* __HAVE_ARCH_PTE_SWP_EXCLUSIVE */
}

--
2.39.0