Subject: [PATCH 1/3] powerpc/64s/radix: make ptep_get_and_clear_full non-atomic for the full case

From: Nicholas Piggin <[email-masked]>
Date: Sun, 13 May 2018 14:21:04 +1000

This matches other architectures, when we know there will be no
further accesses to the address (e.g., for teardown), page table
entries can be cleared non-atomically.

The comments about NMMU are bogus, all MMU notifiers (including NMMU)
are released at this point, with their TLBs flushed. An NMMU access
at this point would be a bug.

Signed-off-by: Nicholas Piggin <[email-masked]>
---
 arch/powerpc/include/asm/book3s/64/radix.h | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/arch/powerpc/include/asm/book3s/64/radix.h b/arch/powerpc/include/asm/book3s/64/radix.h
index 705193e7192f..fcd92f9b6ec0 100644
--- a/arch/powerpc/include/asm/book3s/64/radix.h
+++ b/arch/powerpc/include/asm/book3s/64/radix.h
@@ -176,14 +176,8 @@ static inline pte_t radix__ptep_get_and_clear_full(struct mm_struct *mm,
 	unsigned long old_pte;
 
 	if (full) {
-		/*
-		 * If we are trying to clear the pte, we can skip
-		 * the DD1 pte update sequence and batch the tlb flush. The
-		 * tlb flush batching is done by mmu gather code. We
-		 * still keep the cmp_xchg update to make sure we get
-		 * correct R/C bit which might be updated via Nest MMU.
-		 */
-		old_pte = __radix_pte_update(ptep, ~0ul, 0);
+		old_pte = pte_val(*ptep);
+		*ptep = __pte(0);
 	} else
 		old_pte = radix__pte_update(mm, addr, ptep, ~0ul, 0, 0);
 
-- 
2.17.0