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List:       kvm
Subject:    [PATCH 7/8] KVM: x86: Do not set access bit on accessed segments
From:       Nadav Amit <namit () cs ! technion ! ac ! il>
Date:       2014-12-25 0:52:22
Message-ID: 1419468743-23732-8-git-send-email-namit () cs ! technion ! ac ! il
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When segment is loaded, the segment access bit is set unconditionally.  In
fact, it should be set conditionally, based on whether the segment had the
accessed bit set before. In addition, it can improve performance.

Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
---
 arch/x86/kvm/emulate.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 7bf3548..4fcd9fd 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1620,10 +1620,13 @@ static int __load_segment_descriptor(struct x86_emulate_ctxt *ctxt,
 
 	if (seg_desc.s) {
 		/* mark segment as accessed */
-		seg_desc.type |= 1;
-		ret = write_segment_descriptor(ctxt, selector, &seg_desc);
-		if (ret != X86EMUL_CONTINUE)
-			return ret;
+		if (!(seg_desc.type & 1)) {
+			seg_desc.type |= 1;
+			ret = write_segment_descriptor(ctxt, selector,
+						       &seg_desc);
+			if (ret != X86EMUL_CONTINUE)
+				return ret;
+		}
 	} else if (ctxt->mode == X86EMUL_MODE_PROT64) {
 		ret = ctxt->ops->read_std(ctxt, desc_addr+8, &base3,
 				sizeof(base3), &ctxt->exception);
-- 
1.9.1

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