linux-kernel - [PATCH mm-unstable RFC 01/26] mm/debug_vm_pgtable: more pte_swp

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Date:   Tue,  6 Dec 2022 15:47:05 +0100
From:   David Hildenbrand <david@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        John Hubbard <jhubbard@...dia.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Yang Shi <shy828301@...il.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Nadav Amit <namit@...are.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Peter Xu <peterx@...hat.com>, linux-mm@...ck.org,
        x86@...nel.org, linux-alpha@...r.kernel.org,
        linux-snps-arc@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-csky@...r.kernel.org,
        linux-hexagon@...r.kernel.org, linux-ia64@...r.kernel.org,
        loongarch@...ts.linux.dev, linux-m68k@...ts.linux-m68k.org,
        linux-mips@...r.kernel.org, openrisc@...ts.librecores.org,
        linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-um@...ts.infradead.org, linux-xtensa@...ux-xtensa.org,
        David Hildenbrand <david@...hat.com>
Subject: [PATCH mm-unstable RFC 01/26] mm/debug_vm_pgtable: more pte_swp_exclusive() sanity checks

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@...hat.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 c631ade3f1d2..0506622016d9 100644
--- a/mm/debug_vm_pgtable.c
+++ b/mm/debug_vm_pgtable.c
@@ -807,13 +807,34 @@ 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 */
 }
 
-- 
2.38.1