From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34520) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gXks3-0008TY-A0 for qemu-devel@nongnu.org; Fri, 14 Dec 2018 05:39:09 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gXks0-00056N-EG for qemu-devel@nongnu.org; Fri, 14 Dec 2018 05:39:03 -0500 Received: from mx1.redhat.com ([209.132.183.28]:32820) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gXks0-00055f-54 for qemu-devel@nongnu.org; Fri, 14 Dec 2018 05:39:00 -0500 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 2F56231256B2 for ; Fri, 14 Dec 2018 10:38:59 +0000 (UTC) From: Gerd Hoffmann Date: Fri, 14 Dec 2018 11:38:52 +0100 Message-Id: <20181214103854.13820-4-kraxel@redhat.com> In-Reply-To: <20181214103854.13820-1-kraxel@redhat.com> References: <20181214103854.13820-1-kraxel@redhat.com> Subject: [Qemu-devel] [PULL 3/5] ehci: fix fetch qtd race List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Gerd Hoffmann The token field contains the (guest-filled) state of the qtd, which indicates whenever the other fields are valid or not. So make sure we read the token first, otherwise we may end up with an stale next pointer: (1) ehci reads next (2) guest writes next (3) guest writes token (4) ehci reads token (5) ehci operates with stale next. Typical effect is that qemu doesn't notice that the guest appends new qtds to the end of the queue. Looks like the usb device stopped responding. Linux can recover from that, but leaves a message in the kernel log that it did reset the usb device in question. Signed-off-by: Gerd Hoffmann Message-id: 20181126100836.8805-1-kraxel@redhat.com --- hw/usb/hcd-ehci.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/hw/usb/hcd-ehci.c b/hw/usb/hcd-ehci.c index e5acfc5ba5..8d44d483df 100644 --- a/hw/usb/hcd-ehci.c +++ b/hw/usb/hcd-ehci.c @@ -1783,9 +1783,17 @@ static int ehci_state_fetchqtd(EHCIQueue *q) EHCIqtd qtd; EHCIPacket *p; int again = 1; + uint32_t addr; - if (get_dwords(q->ehci, NLPTR_GET(q->qtdaddr), (uint32_t *) &qtd, - sizeof(EHCIqtd) >> 2) < 0) { + addr = NLPTR_GET(q->qtdaddr); + if (get_dwords(q->ehci, addr + 8, &qtd.token, 1) < 0) { + return 0; + } + barrier(); + if (get_dwords(q->ehci, addr + 0, &qtd.next, 1) < 0 || + get_dwords(q->ehci, addr + 4, &qtd.altnext, 1) < 0 || + get_dwords(q->ehci, addr + 12, qtd.bufptr, + ARRAY_SIZE(qtd.bufptr)) < 0) { return 0; } ehci_trace_qtd(q, NLPTR_GET(q->qtdaddr), &qtd); -- 2.9.3