fs/proc/task_mmu: don't indicate PM_MMAP_EXCLUSIVE without PM_PRESENT

Relying on the mapcount for non-present PTEs that reference pages doesn't
make any sense: they are not accounted in the mapcount, so page_mapcount()
== 1 won't return the result we actually want to know.

While we don't check the mapcount for migration entries already, we could
end up checking it for swap, hwpoison, device exclusive, ...  entries,
which we really shouldn't.

There is one exception: device private entries, which we consider
fake-present (e.g., incremented the mapcount).  But we won't care about
that for now for PM_MMAP_EXCLUSIVE, because indicating PM_SWAP for them
although they are fake-present already sounds suspiciously wrong.

Let's never indicate PM_MMAP_EXCLUSIVE without PM_PRESENT.

Link: https://lkml.kernel.org/r/20240607122357.115423-3-david@redhat.comSigned-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Lance Yang <ioworker0@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/proc/task_mmu.c

@@ -1418,7 +1418,6 @@ static pagemap_entry_t pte_to_pagemap_entry(struct pagemapread *pm,
 {
 	u64 frame = 0, flags = 0;
 	struct page *page = NULL;
-	bool migration = false;
 
 	if (pte_present(pte)) {
 		if (pm->show_pfn)
@@ -1450,7 +1449,6 @@ static pagemap_entry_t pte_to_pagemap_entry(struct pagemapread *pm,
 			    (offset << MAX_SWAPFILES_SHIFT);
 		}
 		flags |= PM_SWAP;
-		migration = is_migration_entry(entry);
 		if (is_pfn_swap_entry(entry))
 			page = pfn_swap_entry_to_page(entry);
 		if (pte_marker_entry_uffd_wp(entry))
@@ -1459,7 +1457,7 @@ static pagemap_entry_t pte_to_pagemap_entry(struct pagemapread *pm,
 
 	if (page && !PageAnon(page))
 		flags |= PM_FILE;
-	if (page && !migration && page_mapcount(page) == 1)
+	if (page && (flags & PM_PRESENT) && page_mapcount(page) == 1)
 		flags |= PM_MMAP_EXCLUSIVE;
 	if (vma->vm_flags & VM_SOFTDIRTY)
 		flags |= PM_SOFT_DIRTY;
@@ -1476,7 +1474,6 @@ static int pagemap_pmd_range(pmd_t *pmdp, unsigned long addr, unsigned long end,
 	pte_t *pte, *orig_pte;
 	int err = 0;
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	bool migration = false;
 
 	ptl = pmd_trans_huge_lock(pmdp, vma);
 	if (ptl) {
@@ -1520,14 +1517,13 @@ static int pagemap_pmd_range(pmd_t *pmdp, unsigned long addr, unsigned long end,
 			if (pmd_swp_uffd_wp(pmd))
 				flags |= PM_UFFD_WP;
 			VM_BUG_ON(!is_pmd_migration_entry(pmd));
-			migration = is_migration_entry(entry);
 			page = pfn_swap_entry_to_page(entry);
 		}
 #endif
 
 		if (page && !PageAnon(page))
 			flags |= PM_FILE;
-		if (page && !migration && page_mapcount(page) == 1)
+		if (page && (flags & PM_PRESENT) && page_mapcount(page) == 1)
 			flags |= PM_MMAP_EXCLUSIVE;
 
 		for (; addr != end; addr += PAGE_SIZE) {