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 X-Spam-Level: X-Spam-Status: No, score=-16.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 91FA0C43460 for ; Wed, 12 May 2021 10:49:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C2FBD613DF for ; Wed, 12 May 2021 10:49:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230268AbhELKu0 (ORCPT ); Wed, 12 May 2021 06:50:26 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:50661 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230230AbhELKuX (ORCPT ); Wed, 12 May 2021 06:50:23 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1620816555; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=g6ZqJG2exIYG7PlPiCBsNSM/rwDZhImxg4IaHwFDE2k=; b=HDYwcy48pwz9ll6XKVZPxaIY0oHuv8ViJGU/4IOmuTEuXzR16apkZgVdnjnNC551DCjPZW kRoLHc9PZTHCahu/7Ryt3VCs2slGIuHg24aHAgfqydb+froiUtxWqeisQZJoVWfMvlGIDs w7nUNrAvuJ5PyazobIAM6c4IaiG1N10= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-557-_C15r1peNO2Xa0wq0Bo3yQ-1; Wed, 12 May 2021 06:49:11 -0400 X-MC-Unique: _C15r1peNO2Xa0wq0Bo3yQ-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 73152100855A; Wed, 12 May 2021 10:49:10 +0000 (UTC) Received: from gondolin.fritz.box (ovpn-113-78.ams2.redhat.com [10.36.113.78]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1DFD15D6A8; Wed, 12 May 2021 10:49:08 +0000 (UTC) Date: Wed, 12 May 2021 12:49:06 +0200 From: Cornelia Huck To: Eric Farman Cc: Matthew Rosato , Halil Pasic , Jared Rossi , linux-s390@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH v6 3/3] vfio-ccw: Serialize FSM IDLE state with I/O completion Message-ID: <20210512124906.709d562c.cohuck@redhat.com> In-Reply-To: <20210511195631.3995081-4-farman@linux.ibm.com> References: <20210511195631.3995081-1-farman@linux.ibm.com> <20210511195631.3995081-4-farman@linux.ibm.com> Organization: Red Hat GmbH MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Tue, 11 May 2021 21:56:31 +0200 Eric Farman wrote: > Today, the stacked call to vfio_ccw_sch_io_todo() does three things: > > 1) Update a solicited IRB with CP information, and release the CP > if the interrupt was the end of a START operation. > 2) Copy the IRB data into the io_region, under the protection of > the io_mutex > 3) Reset the vfio-ccw FSM state to IDLE to acknowledge that > vfio-ccw can accept more work. > > The trouble is that step 3 is (A) invoked for both solicited and > unsolicited interrupts, and (B) sitting after the mutex for step 2. > This second piece becomes a problem if it processes an interrupt > for a CLEAR SUBCHANNEL while another thread initiates a START, > thus allowing the CP and FSM states to get out of sync. That is: > > CPU 1 CPU 2 > fsm_do_clear() > fsm_irq() > fsm_io_request() > vfio_ccw_sch_io_todo() > fsm_io_helper() > > Since the FSM state and CP should be kept in sync, let's make a > note when the CP is released, and rely on that as an indication > that the FSM should also be reset at the end of this routine and > open up the device for more work. > > Signed-off-by: Eric Farman > --- > drivers/s390/cio/vfio_ccw_drv.c | 12 ++++++++++-- > 1 file changed, 10 insertions(+), 2 deletions(-) Looking good :) Reviewed-by: Cornelia Huck