[RFC PATCH 1/1] mm/debug_vm_pgtable: Use a swp_entry_t input value for swap tests

[Gerald Schaefer]

The various __pte/pmd_to_swp_entry and __swp_entry_to_pte/pmd helper
functions are expected to operate on swapped PTE/PMD entries, not on
present and mapped entries.

Reflect this in the swap tests by using a swp_entry_t as input value,
similar to how it is already done in pte_swap_exclusive_tests().
Move the swap entry creation to init_args() and store it in args, so
it can also be used in other functions.

The pte/pmd_swap_tests() are also changed to compare entries instead of
pfn values, because pte/pmd_pfn() helpers are not expected to operate on
swapped entries. E.g. on s390, pmd_pfn() needs different shifts for leaf
(large) and non-leaf PMDs.

Also update documentation, to reflect that the helpers operate on
swapped and not mapped entries, and use correct names, i.e.
__swp_to_pte/pmd_entry -> __swp_entry_to_pte/pmd.

For consistency, also change pte/pmd_swap_soft_dirty_tests() to use
args->swp_entry instead of a present and mapped PTE/PMD.

Signed-off-by: Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx>
---
 Documentation/mm/arch_pgtable_helpers.rst |  8 ++--
 mm/debug_vm_pgtable.c                     | 55 ++++++++++++++---------
 2 files changed, 38 insertions(+), 25 deletions(-)

diff --git a/Documentation/mm/arch_pgtable_helpers.rst b/Documentation/mm/arch_pgtable_helpers.rst
index af245161d8e7..e2ac76202a85 100644
--- a/Documentation/mm/arch_pgtable_helpers.rst
+++ b/Documentation/mm/arch_pgtable_helpers.rst
@@ -242,13 +242,13 @@ SWAP Page Table Helpers
 ========================
 
 +---------------------------+--------------------------------------------------+
-| __pte_to_swp_entry        | Creates a swapped entry (arch) from a mapped PTE |
+| __pte_to_swp_entry        | Creates a swap entry (arch) from a swapped PTE   |
 +---------------------------+--------------------------------------------------+
-| __swp_to_pte_entry        | Creates a mapped PTE from a swapped entry (arch) |
+| __swp_entry_to_pte        | Creates a swapped PTE from a swap entry (arch)   |
 +---------------------------+--------------------------------------------------+
-| __pmd_to_swp_entry        | Creates a swapped entry (arch) from a mapped PMD |
+| __pmd_to_swp_entry        | Creates a swap entry (arch) from a swapped PMD   |
 +---------------------------+--------------------------------------------------+
-| __swp_to_pmd_entry        | Creates a mapped PMD from a swapped entry (arch) |
+| __swp_entry_to_pmd        | Creates a swapped PMD from a swap entry (arch)   |
 +---------------------------+--------------------------------------------------+
 | is_migration_entry        | Tests a migration (read or write) swapped entry  |
 +-------------------------------+----------------------------------------------+
diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
index 7731b238b534..3b0f83ed6c2e 100644
--- a/mm/debug_vm_pgtable.c
+++ b/mm/debug_vm_pgtable.c
@@ -73,6 +73,8 @@ struct pgtable_debug_args {
 	unsigned long		fixed_pud_pfn;
 	unsigned long		fixed_pmd_pfn;
 	unsigned long		fixed_pte_pfn;
+
+	swp_entry_t		swp_entry;
 };
 
 static void __init pte_basic_tests(struct pgtable_debug_args *args, int idx)
@@ -754,12 +756,15 @@ static void __init pte_soft_dirty_tests(struct pgtable_debug_args *args)
 
 static void __init pte_swap_soft_dirty_tests(struct pgtable_debug_args *args)
 {
-	pte_t pte = pfn_pte(args->fixed_pte_pfn, args->page_prot);
+	pte_t pte;
 
 	if (!IS_ENABLED(CONFIG_MEM_SOFT_DIRTY))
 		return;
 
 	pr_debug("Validating PTE swap soft dirty\n");
+	pte = swp_entry_to_pte(args->swp_entry);
+	WARN_ON(!is_swap_pte(pte));
+
 	WARN_ON(!pte_swp_soft_dirty(pte_swp_mksoft_dirty(pte)));
 	WARN_ON(pte_swp_soft_dirty(pte_swp_clear_soft_dirty(pte)));
 }
@@ -793,7 +798,9 @@ static void __init pmd_swap_soft_dirty_tests(struct pgtable_debug_args *args)
 		return;
 
 	pr_debug("Validating PMD swap soft dirty\n");
-	pmd = pfn_pmd(args->fixed_pmd_pfn, args->page_prot);
+	pmd = swp_entry_to_pmd(args->swp_entry);
+	WARN_ON(!is_swap_pmd(pmd));
+
 	WARN_ON(!pmd_swp_soft_dirty(pmd_swp_mksoft_dirty(pmd)));
 	WARN_ON(pmd_swp_soft_dirty(pmd_swp_clear_soft_dirty(pmd)));
 }
@@ -804,17 +811,11 @@ 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)
 {
-	unsigned long max_swap_offset;
 	swp_entry_t entry, entry2;
 	pte_t pte;
 
 	pr_debug("Validating PTE swap exclusive\n");
-
-	/* See generic_max_swapfile_size(): probe the maximum offset */
-	max_swap_offset = swp_offset(pte_to_swp_entry(swp_entry_to_pte(swp_entry(0, ~0UL))));
-
-	/* Create a swp entry with all possible bits set */
-	entry = swp_entry((1 << MAX_SWAPFILES_SHIFT) - 1, max_swap_offset);
+	entry = args->swp_entry;
 
 	pte = swp_entry_to_pte(entry);
 	WARN_ON(pte_swp_exclusive(pte));
@@ -838,30 +839,36 @@ static void __init pte_swap_exclusive_tests(struct pgtable_debug_args *args)
 
 static void __init pte_swap_tests(struct pgtable_debug_args *args)
 {
-	swp_entry_t swp;
-	pte_t pte;
+	swp_entry_t entry, arch_entry;
+	pte_t pte, pte2;
 
 	pr_debug("Validating PTE swap\n");
-	pte = pfn_pte(args->fixed_pte_pfn, args->page_prot);
-	swp = __pte_to_swp_entry(pte);
-	pte = __swp_entry_to_pte(swp);
-	WARN_ON(args->fixed_pte_pfn != pte_pfn(pte));
+	entry = args->swp_entry;
+
+	pte = swp_entry_to_pte(entry);
+	WARN_ON(!is_swap_pte(pte));
+	arch_entry = __pte_to_swp_entry(pte);
+	pte2 = __swp_entry_to_pte(arch_entry);
+	WARN_ON(memcmp(&pte, &pte2, sizeof(pte)));
 }
 
 #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
 static void __init pmd_swap_tests(struct pgtable_debug_args *args)
 {
-	swp_entry_t swp;
-	pmd_t pmd;
+	swp_entry_t entry, arch_entry;
+	pmd_t pmd, pmd2;
 
 	if (!has_transparent_hugepage())
 		return;
 
 	pr_debug("Validating PMD swap\n");
-	pmd = pfn_pmd(args->fixed_pmd_pfn, args->page_prot);
-	swp = __pmd_to_swp_entry(pmd);
-	pmd = __swp_entry_to_pmd(swp);
-	WARN_ON(args->fixed_pmd_pfn != pmd_pfn(pmd));
+	entry = args->swp_entry;
+	pmd = swp_entry_to_pmd(entry);
+	WARN_ON(!is_swap_pmd(pmd));
+
+	arch_entry = __pmd_to_swp_entry(pmd);
+	pmd2 = __swp_entry_to_pmd(arch_entry);
+	WARN_ON(memcmp(&pmd, &pmd2, sizeof(pmd)));
 }
 #else  /* !CONFIG_ARCH_ENABLE_THP_MIGRATION */
 static void __init pmd_swap_tests(struct pgtable_debug_args *args) { }
@@ -1166,6 +1173,7 @@ static void __init init_fixed_pfns(struct pgtable_debug_args *args)
 
 static int __init init_args(struct pgtable_debug_args *args)
 {
+	unsigned long max_swap_offset;
 	struct page *page = NULL;
 	int ret = 0;
 
@@ -1248,6 +1256,11 @@ static int __init init_args(struct pgtable_debug_args *args)
 
 	init_fixed_pfns(args);
 
+	/* See generic_max_swapfile_size(): probe the maximum offset */
+	max_swap_offset = swp_offset(pte_to_swp_entry(swp_entry_to_pte(swp_entry(0, ~0UL))));
+	/* Create a swp entry with all possible bits set */
+	args->swp_entry = swp_entry((1 << MAX_SWAPFILES_SHIFT) - 1, max_swap_offset);
+
 	/*
 	 * Allocate (huge) pages because some of the tests need to access
 	 * the data in the pages. The corresponding tests will be skipped
-- 
2.48.1