From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Mueller Subject: Re: [PATCH v5 10/15] KVM: s390: add functions to (un)register GISC with GISA Date: Mon, 7 Jan 2019 18:38:02 +0100 Message-ID: References: <20181219191756.57973-1-mimu@linux.ibm.com> <20181219191756.57973-11-mimu@linux.ibm.com> <20190104141836.0ca98a77.cohuck@redhat.com> Reply-To: mimu@linux.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Cc: KVM Mailing List , Linux-S390 Mailing List , linux-kernel@vger.kernel.org, Martin Schwidefsky , Heiko Carstens , Christian Borntraeger , Janosch Frank , David Hildenbrand , Halil Pasic To: Cornelia Huck , Pierre Morel Return-path: In-Reply-To: <20190104141836.0ca98a77.cohuck@redhat.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 04.01.19 14:19, Cornelia Huck wrote: > On Wed, 2 Jan 2019 18:29:00 +0100 > Pierre Morel wrote: > >> On 19/12/2018 20:17, Michael Mueller wrote: >>> Add the IAM (Interruption Alert Mask) to the architecture specific >>> kvm struct. This mask in the GISA is used to define for which ISC >>> a GIB alert can be issued. >>> >>> The functions kvm_s390_gisc_register() and kvm_s390_gisc_unregister() >>> are used to (un)register a GISC (guest ISC) with a virtual machine and >>> its GISA. >>> >>> Upon successful completion, kvm_s390_gisc_register() returns the >>> ISC to be used for GIB alert interruptions. A negative return code >>> indicates an error during registration. >>> >>> Theses functions will be used by other adapter types like AP and PCI to >>> request pass-through interruption support. >>> >>> Signed-off-by: Michael Mueller >>> --- >>> arch/s390/include/asm/kvm_host.h | 9 ++++++ >>> arch/s390/kvm/interrupt.c | 66 ++++++++++++++++++++++++++++++++++++++++ >>> 2 files changed, 75 insertions(+) >>> > >>> +int kvm_s390_gisc_register(struct kvm *kvm, u32 gisc) >>> +{ >>> + 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) >>> + kvm->arch.iam |= 0x80 >> gisc; >>> + kvm->arch.iam_ref_count[gisc]++; >>> + if (kvm->arch.iam_ref_count[gisc] == 1) >>> + set_iam(kvm->arch.gisa, kvm->arch.iam); >> >> testing the set_iam return value? >> Even it should be fine if the caller works correctly, this is done >> before GISA is ever used. There is a rc but a check here is not required. There are three cases: a) This is the first ISC that gets registered, then the GISA is not in use and IAM is set in the GISA. b) A second ISC gets registered and the GISA is *not* in the alert list. Then the IAM is set here as well. c) A second ISC gets registered and the GISA is in the alert list. Then the IAM is intentionally not set here by set_iam(). It will be restored by get_ipm() with the new IAM value by the gib alert processing code. > > My feeling is that checking the return code is a good idea, even if it > Should Never Fail(tm). > >> >>> + 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. > >>> + } >>> +out: >>> + spin_unlock(&kvm->arch.iam_ref_lock); >>> + >>> + return rc; >>> +} >>> +EXPORT_SYMBOL_GPL(kvm_s390_gisc_unregister); >>> + >>> void kvm_s390_gib_destroy(void) >>> { >>> if (!gib) >>> >> >> >