[PATCH v3 4/4] mm: pass the number of PTEs to move_pte()

[Imre Kaloz]

Since commit f822a9a81a31 ("mm: optimize mremap() by PTE batching"),
move_ptes() moves a batch of PTEs mapping consecutive pages of a folio
at a time, but calls move_pte() once per batch with the first PTE
only. sparc64, the only architecture that overrides move_pte(), flushes
from the D-cache the page that PTE maps when the move changes its
colour, so the other pages of a batch would keep lines of the old
colour. This cannot happen today only because sparc64 has no
pte_batch_hint(), and mremap_folio_pte_batch() then never batches.

Pass nr_ptes to move_pte(), as get_and_clear_ptes() takes it. The
generic version ignores it, and sparc64 flushes every page of the
batch.

Signed-off-by: Imre Kaloz <kaloz@xxxxxxxxxx>
---
 arch/sparc/include/asm/pgtable_64.h | 16 +++++++++-------
 include/linux/pgtable.h             |  2 +-
 mm/mremap.c                         |  2 +-
 3 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/arch/sparc/include/asm/pgtable_64.h b/arch/sparc/include/asm/pgtable_64.h
index 1430489b9ac5..9ca787b3cbfe 100644
--- a/arch/sparc/include/asm/pgtable_64.h
+++ b/arch/sparc/include/asm/pgtable_64.h
@@ -946,21 +946,23 @@ static inline void set_ptes(struct mm_struct *mm, unsigned long addr,
 	set_pte_at((mm), (addr), (ptep), __pte(0UL))
 
 #ifdef DCACHE_ALIASING_POSSIBLE
-/* This flushes only the page the PTE maps, so it relies on move_ptes()
- * calling it for one PTE at a time, which the default pte_batch_hint()
- * guarantees.
+/* The nr PTEs map consecutive pages of one folio and all move by the
+ * same offset, so either every page of the batch aliases or none does.
  */
 #define __HAVE_ARCH_MOVE_PTE
-#define move_pte(pte, old_addr, new_addr)				\
+#define move_pte(pte, old_addr, new_addr, nr)				\
 ({									\
 	pte_t newpte = (pte);						\
 	if (tlb_type != hypervisor && pte_present(pte)) {		\
 		unsigned long this_pfn = pte_pfn(pte);			\
+		unsigned int i;						\
 									\
 		if (pfn_valid(this_pfn) &&				\
-		    (((old_addr) ^ (new_addr)) & (1 << 13)))		\
-			flush_dcache_page_all(current->mm,		\
-					      pfn_to_page(this_pfn));	\
+		    (((old_addr) ^ (new_addr)) & (1 << 13))) {		\
+			for (i = 0; i < (nr); i++)			\
+				flush_dcache_page_all(current->mm,	\
+					pfn_to_page(this_pfn + i));	\
+		}							\
 	}								\
 	newpte;								\
 })
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 8c093c119e5a..b58c0e98994e 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -1471,7 +1471,7 @@ static inline void arch_swap_restore(swp_entry_t entry, struct folio *folio)
 #endif
 
 #ifndef __HAVE_ARCH_MOVE_PTE
-#define move_pte(pte, old_addr, new_addr)	(pte)
+#define move_pte(pte, old_addr, new_addr, nr)	(pte)
 #endif
 
 #ifndef pte_accessible
diff --git a/mm/mremap.c b/mm/mremap.c
index e8df5cdb0ac9..7fcae7f0082d 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -289,7 +289,7 @@ static int move_ptes(struct pagetable_move_control *pmc,
 			force_flush = true;
 		}
 		pte = get_and_clear_ptes(mm, old_addr, old_ptep, nr_ptes);
-		pte = move_pte(pte, old_addr, new_addr);
+		pte = move_pte(pte, old_addr, new_addr, nr_ptes);
 		pte = move_soft_dirty_pte(pte);
 
 		if (need_clear_uffd_wp && pte_is_uffd_wp_marker(pte))
-- 
2.47.3