linux-kernel - [RFC 04/20] mm/mapping_dirty_helpers: use mmu

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Date:   Sat, 30 Jan 2021 16:11:16 -0800
From:   Nadav Amit <nadav.amit@...il.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     Nadav Amit <namit@...are.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>, Yu Zhao <yuzhao@...gle.com>,
        Nick Piggin <npiggin@...il.com>, x86@...nel.org
Subject: [RFC 04/20] mm/mapping_dirty_helpers: use mmu_gather

From: Nadav Amit <namit@...are.com>

Avoid open-coding mmu_gather for no reason. There is no apparent reason
not to use the existing mmu_gather interfaces.

Use the newly introduced pte_may_need_flush() to check whether a flush
is needed to avoid unnecassary flushes.

Signed-off-by: Nadav Amit <namit@...are.com>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Will Deacon <will@...nel.org>
Cc: Yu Zhao <yuzhao@...gle.com>
Cc: Nick Piggin <npiggin@...il.com>
Cc: x86@...nel.org
---
 mm/mapping_dirty_helpers.c | 37 +++++++++++--------------------------
 1 file changed, 11 insertions(+), 26 deletions(-)

diff --git a/mm/mapping_dirty_helpers.c b/mm/mapping_dirty_helpers.c
index b59054ef2e10..2ce6cf431026 100644
--- a/mm/mapping_dirty_helpers.c
+++ b/mm/mapping_dirty_helpers.c
@@ -4,7 +4,7 @@
 #include <linux/bitops.h>
 #include <linux/mmu_notifier.h>
 #include <asm/cacheflush.h>
-#include <asm/tlbflush.h>
+#include <asm/tlb.h>
 
 /**
  * struct wp_walk - Private struct for pagetable walk callbacks
@@ -15,8 +15,7 @@
  */
 struct wp_walk {
 	struct mmu_notifier_range range;
-	unsigned long tlbflush_start;
-	unsigned long tlbflush_end;
+	struct mmu_gather tlb;
 	unsigned long total;
 };
 
@@ -42,9 +41,9 @@ static int wp_pte(pte_t *pte, unsigned long addr, unsigned long end,
 		ptent = pte_wrprotect(old_pte);
 		ptep_modify_prot_commit(walk->vma, addr, pte, old_pte, ptent);
 		wpwalk->total++;
-		wpwalk->tlbflush_start = min(wpwalk->tlbflush_start, addr);
-		wpwalk->tlbflush_end = max(wpwalk->tlbflush_end,
-					   addr + PAGE_SIZE);
+
+		if (pte_may_need_flush(old_pte, ptent))
+			tlb_flush_pte_range(&wpwalk->tlb, addr, PAGE_SIZE);
 	}
 
 	return 0;
@@ -101,9 +100,7 @@ static int clean_record_pte(pte_t *pte, unsigned long addr,
 		ptep_modify_prot_commit(walk->vma, addr, pte, old_pte, ptent);
 
 		wpwalk->total++;
-		wpwalk->tlbflush_start = min(wpwalk->tlbflush_start, addr);
-		wpwalk->tlbflush_end = max(wpwalk->tlbflush_end,
-					   addr + PAGE_SIZE);
+		tlb_flush_pte_range(&wpwalk->tlb, addr, PAGE_SIZE);
 
 		__set_bit(pgoff, cwalk->bitmap);
 		cwalk->start = min(cwalk->start, pgoff);
@@ -184,20 +181,13 @@ static int wp_clean_pre_vma(unsigned long start, unsigned long end,
 {
 	struct wp_walk *wpwalk = walk->private;
 
-	wpwalk->tlbflush_start = end;
-	wpwalk->tlbflush_end = start;
-
 	mmu_notifier_range_init(&wpwalk->range, MMU_NOTIFY_PROTECTION_PAGE, 0,
 				walk->vma, walk->mm, start, end);
 	mmu_notifier_invalidate_range_start(&wpwalk->range);
 	flush_cache_range(walk->vma, start, end);
 
-	/*
-	 * We're not using tlb_gather_mmu() since typically
-	 * only a small subrange of PTEs are affected, whereas
-	 * tlb_gather_mmu() records the full range.
-	 */
-	inc_tlb_flush_pending(walk->mm);
+	tlb_gather_mmu(&wpwalk->tlb, walk->mm);
+	tlb_start_vma(&wpwalk->tlb, walk->vma);
 
 	return 0;
 }
@@ -212,15 +202,10 @@ static void wp_clean_post_vma(struct mm_walk *walk)
 {
 	struct wp_walk *wpwalk = walk->private;
 
-	if (mm_tlb_flush_nested(walk->mm))
-		flush_tlb_range(walk->vma, wpwalk->range.start,
-				wpwalk->range.end);
-	else if (wpwalk->tlbflush_end > wpwalk->tlbflush_start)
-		flush_tlb_range(walk->vma, wpwalk->tlbflush_start,
-				wpwalk->tlbflush_end);
-
 	mmu_notifier_invalidate_range_end(&wpwalk->range);
-	dec_tlb_flush_pending(walk->mm);
+
+	tlb_end_vma(&wpwalk->tlb, walk->vma);
+	tlb_finish_mmu(&wpwalk->tlb);
 }
 
 /*
-- 
2.25.1