From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stefano Stabellini Subject: Re: [PATCH 31/34] xenbus: use __smp_XXX barriers Date: Mon, 4 Jan 2016 11:58:53 +0000 Message-ID: References: <1451473761-30019-1-git-send-email-mst@redhat.com> <1451473761-30019-32-git-send-email-mst@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1451473761-30019-32-git-send-email-mst@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: "Michael S. Tsirkin" Cc: linux-arch@vger.kernel.org, Arnd Bergmann , Stefano Stabellini , Peter Zijlstra , Andrew Cooper , Konrad Rzeszutek Wilk , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, David Vrabel , xen-devel@lists.xenproject.org, Boris Ostrovsky List-Id: linux-arch.vger.kernel.org On Wed, 30 Dec 2015, Michael S. Tsirkin wrote: > drivers/xen/xenbus/xenbus_comms.c uses > full memory barriers to communicate with the other side. > > For guests compiled with CONFIG_SMP, smp_wmb and smp_mb > would be sufficient, so mb() and wmb() here are only needed if > a non-SMP guest runs on an SMP host. > > Switch to __smp_XXX barriers which serve this exact purpose. > > Signed-off-by: Michael S. Tsirkin Reviewed-by: Stefano Stabellini > This is straight-forward, but untested. > I can either merge this patchset through my tree if this is > acked, or defer this and merge the patchset first, > and xen bits through xen tree afterwards. > > Pls let me know. I think it can go via your tree. However you have missed a few Xen source files which need the same mb/__smb_mb conversions: drivers/xen/grant-table.c drivers/xen/evtchn.c drivers/xen/events/events_fifo.c drivers/xen/xen-scsiback.c drivers/xen/tmem.c drivers/xen/xen-pciback/pci_stub.c drivers/xen/xen-pciback/pciback_ops.c > drivers/xen/xenbus/xenbus_comms.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/drivers/xen/xenbus/xenbus_comms.c b/drivers/xen/xenbus/xenbus_comms.c > index fdb0f33..09b17c7 100644 > --- a/drivers/xen/xenbus/xenbus_comms.c > +++ b/drivers/xen/xenbus/xenbus_comms.c > @@ -123,14 +123,14 @@ int xb_write(const void *data, unsigned len) > avail = len; > > /* Must write data /after/ reading the consumer index. */ > - mb(); > + __smp_mb(); > > memcpy(dst, data, avail); > data += avail; > len -= avail; > > /* Other side must not see new producer until data is there. */ > - wmb(); > + __smp_wmb(); > intf->req_prod += avail; > > /* Implies mb(): other side will see the updated producer. */ > @@ -180,14 +180,14 @@ int xb_read(void *data, unsigned len) > avail = len; > > /* Must read data /after/ reading the producer index. */ > - rmb(); > + __smp_rmb(); > > memcpy(data, src, avail); > data += avail; > len -= avail; > > /* Other side must not see free space until we've copied out */ > - mb(); > + __smp_mb(); > intf->rsp_cons += avail; > > pr_debug("Finished read of %i bytes (%i to go)\n", avail, len); > -- > MST >