Subject: [PATCH 2/3] powerpc/mm/radix: Use ptep_get_and_clear_full when clearing pte for full mm

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Thu, 9 Feb 2017 08:28:20 +0530

This helps us to do some optimization for application exit case, where we can
skip the DD1 style pte update sequence.

Signed-off-by: Aneesh Kumar K.V <[email-masked]>
---
 arch/powerpc/include/asm/book3s/64/pgtable.h | 17 +++++++++++++++++
 arch/powerpc/include/asm/book3s/64/radix.h   | 23 ++++++++++++++++++++++-
 2 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
index 6f15bde94da2..e91ada786d48 100644
--- a/arch/powerpc/include/asm/book3s/64/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
@@ -373,6 +373,23 @@ static inline pte_t ptep_get_and_clear(struct mm_struct *mm,
 	return __pte(old);
 }
 
+#define __HAVE_ARCH_PTEP_GET_AND_CLEAR_FULL
+static inline pte_t ptep_get_and_clear_full(struct mm_struct *mm,
+					    unsigned long addr,
+					    pte_t *ptep, int full)
+{
+	if (full && radix_enabled()) {
+		/*
+		 * Let's skip the DD1 style pte update here. We know that
+		 * this is a full mm pte clear and hence can be sure there is
+		 * no parallel set_pte.
+		 */
+		return radix__ptep_get_and_clear_full(mm, addr, ptep, full);
+	}
+	return ptep_get_and_clear(mm, addr, ptep);
+}
+
+
 static inline void pte_clear(struct mm_struct *mm, unsigned long addr,
 			     pte_t * ptep)
 {
diff --git a/arch/powerpc/include/asm/book3s/64/radix.h b/arch/powerpc/include/asm/book3s/64/radix.h
index 70a3cdcdbe47..fcf822d6c204 100644
--- a/arch/powerpc/include/asm/book3s/64/radix.h
+++ b/arch/powerpc/include/asm/book3s/64/radix.h
@@ -139,7 +139,7 @@ static inline unsigned long radix__pte_update(struct mm_struct *mm,
 
 		unsigned long new_pte;
 
-		old_pte = __radix_pte_update(ptep, ~0, 0);
+		old_pte = __radix_pte_update(ptep, ~0ul, 0);
 		/*
 		 * new value of pte
 		 */
@@ -157,6 +157,27 @@ static inline unsigned long radix__pte_update(struct mm_struct *mm,
 	return old_pte;
 }
 
+static inline pte_t radix__ptep_get_and_clear_full(struct mm_struct *mm,
+						   unsigned long addr,
+						   pte_t *ptep, int full)
+{
+	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);
+	} else
+		old_pte = radix__pte_update(mm, addr, ptep, ~0ul, 0, 0);
+
+	return __pte(old_pte);
+}
+
 /*
  * Set the dirty and/or accessed bits atomically in a linux PTE, this
  * function doesn't need to invalidate tlb.
-- 
2.7.4