mm/x86: make pud_leaf() only care about PSE bit

When working on mprotect() on 1G dax entries, I hit an zap bad pud error
when zapping a huge pud that is with PROT_NONE permission.

Here the problem is x86's pud_leaf() requires both PRESENT and PSE bits
set to report a pud entry as a leaf, but that doesn't look right, as it's
not following the pXd_leaf() definition that we stick with so far, where
PROT_NONE entries should be reported as leaves.

To fix it, change x86's pud_leaf() implementation to only check against
PSE bit to report a leaf, irrelevant of whether PRESENT bit is set.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Peter Xu <[email protected]>
Acked-by: Dave Hansen <[email protected]>
Reviewed-by: David Hildenbrand <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Aneesh Kumar K.V <[email protected]>
Cc: Christophe Leroy <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Dave Jiang <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: "Edgecombe, Rick P" <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Kirill A. Shutemov <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Nicholas Piggin <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Sean Christopherson <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

arch/x86/include/asm/pgtable.h

@@ -1078,8 +1078,7 @@ static inline pmd_t *pud_pgtable(pud_t pud)
 #define pud_leaf pud_leaf
 static inline bool pud_leaf(pud_t pud)
 {
-	return (pud_val(pud) & (_PAGE_PSE | _PAGE_PRESENT)) ==
-		(_PAGE_PSE | _PAGE_PRESENT);
+	return pud_val(pud) & _PAGE_PSE;
 }
 
 static inline int pud_bad(pud_t pud)