linux-kernel - [PATCH] x86/kvm: virt_xxx memory barriers instead of mandatory barriers

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Message-Id: <1491904161-4099-1-git-send-email-wanpeng.li@hotmail.com>
Date:   Tue, 11 Apr 2017 02:49:21 -0700
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: [PATCH] x86/kvm: virt_xxx memory barriers instead of mandatory barriers

From: Wanpeng Li <wanpeng.li@...mail.com>

virt_xxx memory barriers are implemented trivially using the low-level 
__smp_xxx macros, __smp_xxx is equal to a compiler barrier for strong 
TSO memory model, however, mandatory barriers will unconditional add 
memory barriers, this patch replaces the rmb() in kvm_steal_clock() by 
virt_rmb().

Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Radim Krčmář <rkrcmar@...hat.com>
Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
---
 arch/x86/kernel/kvm.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 14f65a5..da5c097 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -396,9 +396,9 @@ static u64 kvm_steal_clock(int cpu)
 	src = &per_cpu(steal_time, cpu);
 	do {
 		version = src->version;
-		rmb();
+		virt_rmb();
 		steal = src->steal;
-		rmb();
+		virt_rmb();
 	} while ((version & 1) || (version != src->version));
 
 	return steal;
-- 
2.7.4