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: Tue, 8 Jan 2019 14:07:06 +0100 Message-ID: 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> Reply-To: mimu@linux.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20190108113444.56e76f13.cohuck@redhat.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Archive: List-Post: To: Cornelia Huck Cc: Pierre Morel , KVM Mailing List , Linux-S390 Mailing List , linux-kernel@vger.kernel.org, Martin Schwidefsky , Heiko Carstens , Christian Borntraeger , Janosch Frank , David Hildenbrand , Halil Pasic List-ID: On 08.01.19 11:34, Cornelia Huck wrote: > On Mon, 7 Jan 2019 18:38:02 +0100 > Michael Mueller wrote: > >> 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. > > 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? > > Apologies if I sound confused (well, that's because I probably am); > this is hard to review without access to the hardware specification. I think nothing will happen because the AP CLR IRQ call (Pierre?) has already taken offline the last AP device. > >> >>> >>>>> + } >>>>> +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) >>>>> >>>> >>>> >>> >> >