From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH] x86/kvm: virt_xxx memory barriers instead of mandatory barriers Date: Tue, 11 Apr 2017 10:20:16 -0400 (EDT) Message-ID: <1672616786.12797852.1491920416876.JavaMail.zimbra@redhat.com> References: <1491904161-4099-1-git-send-email-wanpeng.li@hotmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Radim =?utf-8?B?S3LEjW3DocWZ?= , Wanpeng Li To: Wanpeng Li Return-path: In-Reply-To: <1491904161-4099-1-git-send-email-wanpeng.li@hotmail.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org ----- Original Message ----- > From: "Wanpeng Li" > To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org > Cc: "Paolo Bonzini" , "Radim Krčmář" , "Wanpeng Li" > Sent: Tuesday, April 11, 2017 5:49:21 PM > Subject: [PATCH] x86/kvm: virt_xxx memory barriers instead of mandatory barriers > > From: Wanpeng Li > > 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 > Cc: Radim Krčmář > Signed-off-by: Wanpeng Li > --- > 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 Reviewed-by: Paolo Bonzini