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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 26115C43387 for ; Tue, 8 Jan 2019 13:41:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EC07B20850 for ; Tue, 8 Jan 2019 13:41:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728211AbfAHNlp (ORCPT ); Tue, 8 Jan 2019 08:41:45 -0500 Received: from mx1.redhat.com ([209.132.183.28]:49163 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727236AbfAHNlo (ORCPT ); Tue, 8 Jan 2019 08:41:44 -0500 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id C7DB13E2D0; Tue, 8 Jan 2019 13:41:43 +0000 (UTC) Received: from gondolin (dhcp-192-222.str.redhat.com [10.33.192.222]) by smtp.corp.redhat.com (Postfix) with ESMTP id AD80F100164E; Tue, 8 Jan 2019 13:41:37 +0000 (UTC) Date: Tue, 8 Jan 2019 14:41:35 +0100 From: Cornelia Huck To: Halil Pasic Cc: Michael Mueller , Pierre Morel , KVM Mailing List , Linux-S390 Mailing List , linux-kernel@vger.kernel.org, Martin Schwidefsky , Heiko Carstens , Christian Borntraeger , Janosch Frank , David Hildenbrand Subject: Re: [PATCH v5 10/15] KVM: s390: add functions to (un)register GISC with GISA Message-ID: <20190108144135.3fe5c23b.cohuck@redhat.com> In-Reply-To: <20190108143613.2ca1a9d3@oc2783563651> References: <20181219191756.57973-1-mimu@linux.ibm.com> <20181219191756.57973-11-mimu@linux.ibm.com> <20190104141836.0ca98a77.cohuck@redhat.com> <20190108113444.56e76f13.cohuck@redhat.com> <20190108143613.2ca1a9d3@oc2783563651> Organization: Red Hat GmbH MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Tue, 08 Jan 2019 13:41:44 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 8 Jan 2019 14:36:13 +0100 Halil Pasic wrote: > On Tue, 8 Jan 2019 11:34:44 +0100 > Cornelia Huck wrote: > > > > >> > > > >>> + spin_unlock(&kvm->arch.iam_ref_lock); > > > >>> + > > > >>> + return gib->nisc; > > > >>> +} > > > >>> +EXPORT_SYMBOL_GPL(kvm_s390_gisc_register); > > > >>> + > > > >>> +int kvm_s390_gisc_unregister(struct kvm *kvm, u32 gisc) > > > >>> +{ > > > >>> + int rc = 0; > > > >>> + > > > >>> + if (!kvm->arch.gib_in_use) > > > >>> + return -ENODEV; > > > >>> + if (gisc > MAX_ISC) > > > >>> + return -ERANGE; > > > >>> + > > > >>> + spin_lock(&kvm->arch.iam_ref_lock); > > > >>> + if (kvm->arch.iam_ref_count[gisc] == 0) { > > > >>> + rc = -EINVAL; > > > >>> + goto out; > > > >>> + } > > > >>> + kvm->arch.iam_ref_count[gisc]--; > > > >>> + if (kvm->arch.iam_ref_count[gisc] == 0) { > > > >>> + kvm->arch.iam &= ~(0x80 >> gisc); > > > >>> + set_iam(kvm->arch.gisa, kvm->arch.iam); > > > > > > > > Any chance of this function failing here? If yes, would there be any > > > > implications? > > > > > > It is the same here. > > > > I'm not sure that I follow: This is the reverse operation > > (unregistering the gisc). Can we rely on get_ipm() to do any fixup > > later? Is that a problem for the caller? > > IMHO gib alerts are all about not loosing initiative. I.e. avoiding > substantially delayed delivery of interrupts due to vCPUs in wait > state. > > Thus we must avoid letting go before setting up stuff (gisa.iam under > consideration of gisa ipm, gisa.next_alert, and gib.alert_list_origin) > so that we can react on the next interrupt (if necessary). > > On the other hand, getting more gisa alerts than necessary is not > fatal -- better avoided if not too much hassle of course. Yes, unless the caller does not expect any more alerts after unregistering (I guess that's what you're saying?) > > Bottom line is, while it may be critical that the IAM changes implied > by register take place immediately, unregister is a different story. It does feel a bit weird, though. But maybe I just have trouble grasping the design :/