Subject: [RFC PATCH 1/3] Revert "mm: always flush VMA ranges affected by zap_page_range"

From: Nicholas Piggin <[email-masked]>
Date: Tue, 12 Jun 2018 17:16:19 +1000

This reverts commit 4647706ebeee6e50f7b9f922b095f4ec94d581c3.

Patch 99baac21e4585 ("mm: fix MADV_[FREE|DONTNEED] TLB flush miss
problem") provides a superset of the TLB flush coverage of this
commit, and even includes in the changelog "this patch supersedes
'mm: Always flush VMA ranges affected by zap_page_range v2'".

Reverting this avoids double flushing the TLB range, and the less
efficient flush_tlb_range() call (the mmu_gather API is more precise
about what ranges it invalidates).

Signed-off-by: Nicholas Piggin <[email-masked]>
---
 mm/memory.c | 14 +-------------
 1 file changed, 1 insertion(+), 13 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 7206a634270b..9d472e00fc2d 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1603,20 +1603,8 @@ void zap_page_range(struct vm_area_struct *vma, unsigned long start,
 	tlb_gather_mmu(&tlb, mm, start, end);
 	update_hiwater_rss(mm);
 	mmu_notifier_invalidate_range_start(mm, start, end);
-	for ( ; vma && vma->vm_start < end; vma = vma->vm_next) {
+	for ( ; vma && vma->vm_start < end; vma = vma->vm_next)
 		unmap_single_vma(&tlb, vma, start, end, NULL);
-
-		/*
-		 * zap_page_range does not specify whether mmap_sem should be
-		 * held for read or write. That allows parallel zap_page_range
-		 * operations to unmap a PTE and defer a flush meaning that
-		 * this call observes pte_none and fails to flush the TLB.
-		 * Rather than adding a complex API, ensure that no stale
-		 * TLB entries exist when this call returns.
-		 */
-		flush_tlb_range(vma, start, end);
-	}
-
 	mmu_notifier_invalidate_range_end(mm, start, end);
 	tlb_finish_mmu(&tlb, start, end);
 }
-- 
2.17.0