From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?windows-1252?Q?J=FCrgen_Gro=DF?= Date: Thu, 15 Jan 2015 09:26:47 +0000 Subject: Re: [PATCH 3/8] x86/xen/p2m: Replace ACCESS_ONCE with READ_ONCE Message-Id: <54B787D7.7040202@suse.com> List-Id: 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> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit 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 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?idX145) > > 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 */ >