From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1N2PU7-0002fi-Pp for qemu-devel@nongnu.org; Mon, 26 Oct 2009 09:19:43 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1N2PU3-0002d9-Rr for qemu-devel@nongnu.org; Mon, 26 Oct 2009 09:19:43 -0400 Received: from [199.232.76.173] (port=45701 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1N2PU3-0002cy-M1 for qemu-devel@nongnu.org; Mon, 26 Oct 2009 09:19:39 -0400 Received: from mx1.redhat.com ([209.132.183.28]:32681) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1N2PU3-0002dM-9D for qemu-devel@nongnu.org; Mon, 26 Oct 2009 09:19:39 -0400 Date: Mon, 26 Oct 2009 15:17:15 +0200 From: "Michael S. Tsirkin" Message-ID: <20091026131715.GA25271@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Subject: [Qemu-devel] [PATCH] qemu/virtio: make wmb compiler barrier + comments List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org, anthony@codemonkey.ws wmb must be at least a compiler barrier, even without SMP. Further, we likely need some rmb()/mb() as well: I have not audited the code but lguest has mb(), add a comment for now. Signed-off-by: Michael S. Tsirkin --- hw/virtio.c | 5 ++++- 1 files changed, 4 insertions(+), 1 deletions(-) diff --git a/hw/virtio.c b/hw/virtio.c index 337ff27..1f92171 100644 --- a/hw/virtio.c +++ b/hw/virtio.c @@ -23,8 +23,11 @@ /* QEMU doesn't strictly need write barriers since everything runs in * lock-step. We'll leave the calls to wmb() in though to make it obvious for * KVM or if kqemu gets SMP support. + * In any case, we must prevent the compiler from reordering the code. + * TODO: we likely need some rmb()/mb() as well. */ -#define wmb() do { } while (0) + +#define wmb() __asm__ __volatile__("": : :"memory") typedef struct VRingDesc { -- 1.6.5.rc2