From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 3FEF8C7619A for ; Mon, 27 Mar 2023 11:06:58 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pgkgN-0000W0-Iw; Mon, 27 Mar 2023 07:06:35 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pgkgG-0000VW-Eh for qemu-devel@nongnu.org; Mon, 27 Mar 2023 07:06:29 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pgkgD-0007g6-U2 for qemu-devel@nongnu.org; Mon, 27 Mar 2023 07:06:27 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1679915185; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=nsmXDR8u1aaKmpqf9RrZbEhTfizZ6L8GaqQVdTK14Ys=; b=DOw+lKDtUFwAwu8INlHDhS5R7NBq9SpwbvmljFU1oO1ES2YjBusTVC8Pjq6XkEtlCe52/0 fr5Boy3fURQWeb9yYaFR8ifV1vr6yYQOJgynZGJPQJp4jbq4mrIrwpUAQ2uJWPyZZON552 hwYBNSdp3g5irl/gkgrpyC0gGYhyk0o= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-491-adNNmPJiOdKCPWVeZCFkUA-1; Mon, 27 Mar 2023 07:06:21 -0400 X-MC-Unique: adNNmPJiOdKCPWVeZCFkUA-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id C1690185A7A9; Mon, 27 Mar 2023 11:06:20 +0000 (UTC) Received: from localhost (unknown [10.39.193.145]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 71BC24020C83; Mon, 27 Mar 2023 11:06:20 +0000 (UTC) From: Cornelia Huck To: Halil Pasic Cc: Carlos =?utf-8?Q?L=C3=B3pez?= , qemu-devel@nongnu.org, "Michael S. Tsirkin" , Eric Farman , Richard Henderson , David Hildenbrand , Ilya Leoshkevich , Christian Borntraeger , Thomas Huth , "open list:virtio-ccw" , Halil Pasic Subject: Re: [PATCH v2] virtio: refresh vring region cache after updating a virtqueue size In-Reply-To: <20230322182433.695270d0.pasic@linux.ibm.com> Organization: Red Hat GmbH References: <20230317002749.27379-1-clopez@suse.de> <87y1npglk0.fsf@redhat.com> <20230322182433.695270d0.pasic@linux.ibm.com> User-Agent: Notmuch/0.37 (https://notmuchmail.org) Date: Mon, 27 Mar 2023 13:06:19 +0200 Message-ID: <877cv2sbbo.fsf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 Received-SPF: pass client-ip=170.10.129.124; envelope-from=cohuck@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Wed, Mar 22 2023, Halil Pasic wrote: > On Wed, 22 Mar 2023 10:52:31 +0100 > Cornelia Huck wrote: > [..] >> > >> > diff --git a/hw/s390x/virtio-ccw.c b/hw/s390x/virtio-ccw.c >> > index e33e5207ab..f44de1a8c1 100644 >> > --- a/hw/s390x/virtio-ccw.c >> > +++ b/hw/s390x/virtio-ccw.c >> > @@ -237,6 +237,7 @@ static int virtio_ccw_set_vqs(SubchDev *sch, VqInfoBlock *info, >> > return -EINVAL; >> > } >> > virtio_queue_set_num(vdev, index, num); >> > + virtio_init_region_cache(vdev, index); >> >> Hmm... this is not wrong, but looking at it again, I see that the guest >> has no way to change num after our last call to >> virtio_init_region_cache() (while setting up the queue addresses.) IOW, >> this introduces an extra round trip that is not really needed. >> > > I don't quite understand. AFAIU the virtio_init_region_cache() would see > the (new) queue addresses but not the new size (num). Yes virtio-ccw > already knows the new num but it is yet to call > to put it into vdev->vq[n].vring.num from where > virtio_init_region_cache() picks it up. > > If we were to first virtio_queue_set_num() and only then the address > I would understand. But with the code as is, I don't. Am I missing > something? Hrm, virtio_queue_set_rings() doesn't pass num, I thought it did... I wonder whether ordering virtio_queue_set_num() before it would be better anyway (if the guest gave us an invalid num, we don't need to setup any addresses and init any caches). Smth like if (info) { if (desc) { if (virtio_queue_get_max_num(...) < num) { return -EINVAL; } virtio_queue_set_num(...); } virtio_queue_set_rings(...); } else { /* legacy */ if (desc && virtio_queue_get_max_num(...) > num) { return -EINVAL; } virtio_queue_set_addr(...); } virtio_queue_set_vector(vdev, index, desc ? index : VIRTIO_NO_VECTOR); might be easier to follow than the current code. Or we could just go with this patch, which has the advantage of already existing :)