fs/proc/task_mmu: fix PAGE_IS_PFNZERO detection for the huge zero folio

is_zero_pfn() does not work for the huge zero folio. Fix it by using
is_huge_zero_pmd().

This can cause the PAGEMAP_SCAN ioctl against /proc/pid/pagemap to
present pages as PAGE_IS_PRESENT rather than as PAGE_IS_PFNZERO.

Found by code inspection.

Link: https://lkml.kernel.org/r/20250617143532.2375383-1-david@redhat.com
Fixes: 52526ca ("fs/proc/task_mmu: implement IOCTL to get and optionally clear info about PTEs")
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: davidhildenbrand

fs/proc/task_mmu.c

@@ -2182,7 +2182,7 @@ static unsigned long pagemap_thp_category(struct pagemap_scan_private *p,
 				categories |= PAGE_IS_FILE;
 		}
 
-		if (is_zero_pfn(pmd_pfn(pmd)))
+		if (is_huge_zero_pmd(pmd))
 			categories |= PAGE_IS_PFNZERO;
 		if (pmd_soft_dirty(pmd))
 			categories |= PAGE_IS_SOFT_DIRTY;