[PATCH RFC 01/14] mm/memory: drop highest_memmap_pfn sanity check in vm_normal_page()

[David Hildenbrand]

In 2009, we converted a VM_BUG_ON(!pfn_valid(pfn)) to the current
highest_memmap_pfn sanity check in commit 22b31eec63e5 ("badpage:
vm_normal_page use print_bad_pte"), because highest_memmap_pfn was
readily available.

Nowadays, this is the last remaining highest_memmap_pfn user, and this
sanity check is not really triggering ... frequently.

Let's convert it to VM_WARN_ON_ONCE(!pfn_valid(pfn)), so we can
simplify and get rid of highest_memmap_pfn. Checking for
pfn_to_online_page() might be even better, but it would not handle
ZONE_DEVICE properly.

Do the same in vm_normal_page_pmd(), where we don't even report a
problem at all ...

What might be better in the future is having a runtime option like
page-table-check to enable such checks dynamically on-demand. Something
for the future.

Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
 mm/memory.c | 15 +++------------
 1 file changed, 3 insertions(+), 12 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 0163d127cece9..188b84ebf479a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -590,7 +590,7 @@ struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
 
 	if (IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL)) {
 		if (likely(!pte_special(pte)))
-			goto check_pfn;
+			goto out;
 		if (vma->vm_ops && vma->vm_ops->find_special_page)
 			return vma->vm_ops->find_special_page(vma, addr);
 		if (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP))
@@ -608,9 +608,6 @@ struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
 		if (vma->vm_flags & VM_MIXEDMAP) {
 			if (!pfn_valid(pfn))
 				return NULL;
-			if (is_zero_pfn(pfn))
-				return NULL;
-			goto out;
 		} else {
 			unsigned long off;
 			off = (addr - vma->vm_start) >> PAGE_SHIFT;
@@ -624,17 +621,12 @@ struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
 	if (is_zero_pfn(pfn))
 		return NULL;
 
-check_pfn:
-	if (unlikely(pfn > highest_memmap_pfn)) {
-		print_bad_pte(vma, addr, pte, NULL);
-		return NULL;
-	}
-
 	/*
 	 * NOTE! We still have PageReserved() pages in the page tables.
 	 * eg. VDSO mappings can cause them to exist.
 	 */
 out:
+	VM_WARN_ON_ONCE(!pfn_valid(pfn));
 	VM_WARN_ON_ONCE(is_zero_pfn(pfn));
 	return pfn_to_page(pfn);
 }
@@ -676,14 +668,13 @@ struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr,
 
 	if (is_huge_zero_pmd(pmd))
 		return NULL;
-	if (unlikely(pfn > highest_memmap_pfn))
-		return NULL;
 
 	/*
 	 * NOTE! We still have PageReserved() pages in the page tables.
 	 * eg. VDSO mappings can cause them to exist.
 	 */
 out:
+	VM_WARN_ON_ONCE(!pfn_valid(pfn));
 	return pfn_to_page(pfn);
 }
 
-- 
2.49.0