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List:       kvm
Subject:    [RFC PATCH 1/4] uprobes: use set_pte_at() not set_pte_at_notify()
From:       jglisse () redhat ! com
Date:       2019-01-31 18:37:03
Message-ID: 20190131183706.20980-2-jglisse () redhat ! com
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From: Jérôme Glisse <jglisse@redhat.com>

Using set_pte_at_notify() trigger useless calls to change_pte() so just
use set_pte_at() instead. The reason is that set_pte_at_notify() should
only be use when going from either a read and write pte to read only pte
with same pfn, or from read only to read and write with a different pfn.

The set_pte_at_notify() was use because __replace_page() code came from
the mm/ksm.c code in which the above rules are valid.

Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: kvm@vger.kernel.org
---
 kernel/events/uprobes.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 87e76a1dc758..a4807b1edd7f 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -207,8 +207,7 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
 
 	flush_cache_page(vma, addr, pte_pfn(*pvmw.pte));
 	ptep_clear_flush_notify(vma, addr, pvmw.pte);
-	set_pte_at_notify(mm, addr, pvmw.pte,
-			mk_pte(new_page, vma->vm_page_prot));
+	set_pte_at(mm, addr, pvmw.pte, mk_pte(new_page, vma->vm_page_prot));
 
 	page_remove_rmap(old_page, false);
 	if (!page_mapped(old_page))
-- 
2.17.1

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