From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753285AbbG2N3J (ORCPT ); Wed, 29 Jul 2015 09:29:09 -0400 Received: from mail-wi0-f170.google.com ([209.85.212.170]:35394 "EHLO mail-wi0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750910AbbG2N3G (ORCPT ); Wed, 29 Jul 2015 09:29:06 -0400 From: Paolo Bonzini To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: mtosatti@redhat.com, srutherford@google.com, rkrcmar@redhat.com Subject: [PATCH 1/4] KVM: x86: remove unnecessary memory barriers for shared MSRs Date: Wed, 29 Jul 2015 15:28:55 +0200 Message-Id: <1438176538-26191-2-git-send-email-pbonzini@redhat.com> X-Mailer: git-send-email 1.8.3.1 In-Reply-To: <1438176538-26191-1-git-send-email-pbonzini@redhat.com> References: <1438176538-26191-1-git-send-email-pbonzini@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org There is no smp_rmb matching the smp_wmb. shared_msr_update is called from hardware_enable, which in turn is called via on_each_cpu. on_each_cpu and must imply a read memory barrier (on x86 the rmb is achieved simply through asm volatile in native_apic_mem_write). Signed-off-by: Paolo Bonzini --- arch/x86/kvm/x86.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index c675ea3351cf..2d62229aac26 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -222,11 +222,9 @@ static void shared_msr_update(unsigned slot, u32 msr) void kvm_define_shared_msr(unsigned slot, u32 msr) { BUG_ON(slot >= KVM_NR_SHARED_MSRS); + shared_msrs_global.msrs[slot] = msr; if (slot >= shared_msrs_global.nr) shared_msrs_global.nr = slot + 1; - shared_msrs_global.msrs[slot] = msr; - /* we need ensured the shared_msr_global have been updated */ - smp_wmb(); } EXPORT_SYMBOL_GPL(kvm_define_shared_msr); -- 1.8.3.1