From patchwork Wed Jun 24 13:49:27 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Michael S. Tsirkin" X-Patchwork-Id: 6667811 Return-Path: X-Original-To: patchwork-kvm@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork1.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork1.web.kernel.org (Postfix) with ESMTP id D67A89F1C1 for ; Wed, 24 Jun 2015 13:49:58 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 093F0206DC for ; Wed, 24 Jun 2015 13:49:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F0F42206D9 for ; Wed, 24 Jun 2015 13:49:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753435AbbFXNth (ORCPT ); Wed, 24 Jun 2015 09:49:37 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43543 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752870AbbFXNtb (ORCPT ); Wed, 24 Jun 2015 09:49:31 -0400 Received: from int-mx14.intmail.prod.int.phx2.redhat.com (int-mx14.intmail.prod.int.phx2.redhat.com [10.5.11.27]) by mx1.redhat.com (Postfix) with ESMTPS id AF8C2BC6DF; Wed, 24 Jun 2015 13:49:30 +0000 (UTC) Received: from redhat.com (ovpn-116-21.ams2.redhat.com [10.36.116.21]) by int-mx14.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with SMTP id t5ODnReC009446; Wed, 24 Jun 2015 09:49:28 -0400 Date: Wed, 24 Jun 2015 15:49:27 +0200 From: "Michael S. Tsirkin" To: linux-kernel@vger.kernel.org Cc: Igor Mammedov , Paolo Bonzini , kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-api@vger.kernel.org Subject: [PATCH RFC] vhost: add ioctl to query nregions upper limit Message-ID: <1435153753-2686-1-git-send-email-mst@redhat.com> MIME-Version: 1.0 Content-Disposition: inline X-Mutt-Fcc: =sent X-Scanned-By: MIMEDefang 2.68 on 10.5.11.27 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org X-Spam-Status: No, score=-8.3 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Userspace currently simply tries to give vhost as many regions as it happens to have, but you only have the mem table when you have initialized a large part of VM, so graceful failure is very hard to support. The result is that userspace tends to fail catastrophically. Instead, add a new ioctl so userspace can find out how much kernel supports, up front. This returns a positive value that we commit to. Also, document our contract with legacy userspace: when running on an old kernel, you get -1 and you can assume at least 64 slots. Since 0 value's left unused, let's make that mean that the current userspace behaviour (trial and error) is required, just in case we want it back. Signed-off-by: Michael S. Tsirkin Cc: Igor Mammedov Cc: Paolo Bonzini --- include/uapi/linux/vhost.h | 17 ++++++++++++++++- drivers/vhost/vhost.c | 5 +++++ 2 files changed, 21 insertions(+), 1 deletion(-) diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h index ab373191..f71fa6d 100644 --- a/include/uapi/linux/vhost.h +++ b/include/uapi/linux/vhost.h @@ -80,7 +80,7 @@ struct vhost_memory { * Allows subsequent call to VHOST_OWNER_SET to succeed. */ #define VHOST_RESET_OWNER _IO(VHOST_VIRTIO, 0x02) -/* Set up/modify memory layout */ +/* Set up/modify memory layout: see also VHOST_GET_MEM_MAX_NREGIONS below. */ #define VHOST_SET_MEM_TABLE _IOW(VHOST_VIRTIO, 0x03, struct vhost_memory) /* Write logging setup. */ @@ -127,6 +127,21 @@ struct vhost_memory { /* Set eventfd to signal an error */ #define VHOST_SET_VRING_ERR _IOW(VHOST_VIRTIO, 0x22, struct vhost_vring_file) +/* Query upper limit on nregions in VHOST_SET_MEM_TABLE arguments. + * Returns: + * 0 < value <= MAX_INT - gives the upper limit, higher values will fail + * 0 - there's no static limit: try and see if it works + * -1 - on failure + */ +#define VHOST_GET_MEM_MAX_NREGIONS _IO(VHOST_VIRTIO, 0x23) + +/* Returned by VHOST_GET_MEM_MAX_NREGIONS to mean there's no static limit: + * try and it'll work if you are lucky. */ +#define VHOST_MEM_MAX_NREGIONS_NONE 0 +/* We support at least as many nregions in VHOST_SET_MEM_TABLE: + * for use on legacy kernels without VHOST_GET_MEM_MAX_NREGIONS support. */ +#define VHOST_MEM_MAX_NREGIONS_DEFAULT 64 + /* VHOST_NET specific defines */ /* Attach virtio net ring to a raw socket, or tap device. diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index 9e8e004..3b68f9d 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -917,6 +917,11 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp) long r; int i, fd; + if (ioctl == VHOST_GET_MEM_MAX_NREGIONS) { + r = VHOST_MEMORY_MAX_NREGIONS; + goto done; + } + /* If you are not the owner, you can become one */ if (ioctl == VHOST_SET_OWNER) { r = vhost_dev_set_owner(d);