From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752616AbbAOJ0z (ORCPT ); Thu, 15 Jan 2015 04:26:55 -0500 Received: from cantor2.suse.de ([195.135.220.15]:46085 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751992AbbAOJ0v (ORCPT ); Thu, 15 Jan 2015 04:26:51 -0500 Message-ID: <54B787D7.7040202@suse.com> Date: Thu, 15 Jan 2015 10:26:47 +0100 From: =?windows-1252?Q?J=FCrgen_Gro=DF?= User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 MIME-Version: 1.0 To: Christian Borntraeger , linux-kernel@vger.kernel.org CC: linux-arch@vger.kernel.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, x86@kernel.org, xen-devel@lists.xenproject.org, linux-mm@kvack.org Subject: Re: [PATCH 3/8] x86/xen/p2m: Replace ACCESS_ONCE with READ_ONCE References: <1421312314-72330-1-git-send-email-borntraeger@de.ibm.com> <1421312314-72330-4-git-send-email-borntraeger@de.ibm.com> In-Reply-To: <1421312314-72330-4-git-send-email-borntraeger@de.ibm.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/15/2015 09:58 AM, Christian Borntraeger wrote: > ACCESS_ONCE does not work reliably on non-scalar types. For > example gcc 4.6 and 4.7 might remove the volatile tag for such > accesses during the SRA (scalar replacement of aggregates) step > (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145) > > Change the p2m code to replace ACCESS_ONCE with READ_ONCE. > > Signed-off-by: Christian Borntraeger Reviewed-by: Juergen Gross > --- > arch/x86/xen/p2m.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c > index edbc7a6..cb71016 100644 > --- a/arch/x86/xen/p2m.c > +++ b/arch/x86/xen/p2m.c > @@ -554,7 +554,7 @@ static bool alloc_p2m(unsigned long pfn) > mid_mfn = NULL; > } > > - p2m_pfn = pte_pfn(ACCESS_ONCE(*ptep)); > + p2m_pfn = pte_pfn(READ_ONCE(*ptep)); > if (p2m_pfn == PFN_DOWN(__pa(p2m_identity)) || > p2m_pfn == PFN_DOWN(__pa(p2m_missing))) { > /* p2m leaf page is missing */ >