mm: drop is_huge_zero_pud()

It constantly returns false since 2017.  One assertion is added in 2019 but
it should never have triggered, IOW it means what is checked should be
asserted instead.

If it didn't exist for 7 years maybe it's good idea to remove it and only
add it when it comes.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Peter Xu <[email protected]>
Reviewed-by: Jason Gunthorpe <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Aneesh Kumar K.V <[email protected]>
Cc: Alexander Gordeev <[email protected]>
Cc: Alex Williamson <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Christian Borntraeger <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Gavin Shan <[email protected]>
Cc: Gerald Schaefer <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Niklas Schnelle <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Ryan Roberts <[email protected]>
Cc: Sean Christopherson <[email protected]>
Cc: Sven Schnelle <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Vasily Gorbik <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Zi Yan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: xzpeter

include/linux/huge_mm.h

@@ -433,11 +433,6 @@ static inline bool is_huge_zero_pmd(pmd_t pmd)
 	return pmd_present(pmd) && READ_ONCE(huge_zero_pfn) == pmd_pfn(pmd);
 }
 
-static inline bool is_huge_zero_pud(pud_t pud)
-{
-	return false;
-}
-
 struct folio *mm_get_huge_zero_folio(struct mm_struct *mm);
 void mm_put_huge_zero_folio(struct mm_struct *mm);
 
@@ -578,11 +573,6 @@ static inline bool is_huge_zero_pmd(pmd_t pmd)
 	return false;
 }
 
-static inline bool is_huge_zero_pud(pud_t pud)
-{
-	return false;
-}
-
 static inline void mm_put_huge_zero_folio(struct mm_struct *mm)
 {
 	return;

mm/huge_memory.c

@@ -1453,10 +1453,8 @@ static void insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr,
 	ptl = pud_lock(mm, pud);
 	if (!pud_none(*pud)) {
 		if (write) {
-			if (pud_pfn(*pud) != pfn_t_to_pfn(pfn)) {
-				WARN_ON_ONCE(!is_huge_zero_pud(*pud));
+			if (WARN_ON_ONCE(pud_pfn(*pud) != pfn_t_to_pfn(pfn)))
 				goto out_unlock;
-			}
 			entry = pud_mkyoung(*pud);
 			entry = maybe_pud_mkwrite(pud_mkdirty(entry), vma);
 			if (pudp_set_access_flags(vma, addr, pud, entry, 1))
@@ -1704,15 +1702,6 @@ int copy_huge_pud(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 	if (unlikely(!pud_trans_huge(pud) && !pud_devmap(pud)))
 		goto out_unlock;
 
-	/*
-	 * When page table lock is held, the huge zero pud should not be
-	 * under splitting since we don't split the page itself, only pud to
-	 * a page table.
-	 */
-	if (is_huge_zero_pud(pud)) {
-		/* No huge zero pud yet */
-	}
-
 	/*
 	 * TODO: once we support anonymous pages, use
 	 * folio_try_dup_anon_rmap_*() and split if duplicating fails.