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Thu, 3 Sep 2026 08:38:58 +0000 (GMT) Date: Thu, 3 Sep 2026 10:38:57 +0200 From: Steffen Eiden To: Sean Christopherson Cc: kvm@vger.kernel.org, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, Alexander Gordeev , Andreas Grapentin , Arnd Bergmann , Catalin Marinas , Christian Borntraeger , Claudio Imbrenda , David Hildenbrand , Friedrich Welter , Fuad Tabba , Gautam Gala , Hariharan Mari , Heiko Carstens , Hendrik Brueckner , Ilya Leoshkevich , Janosch Frank , Joey Gouly , Marc Zyngier , Nico Boehr , Nina Schoetterl-Glausch , Oliver Upton , Paolo Bonzini , Suzuki K Poulose , Sven Schnelle , Ulrich Weigand , Vasily Gorbik , Will Deacon , Zenghui Yu Subject: Re: [PATCH v7 23/23] KVM: s390: arm64: Add KVM_S390_ARM64 Kconfig and Makefile Message-ID: <20260903083857.33034-B-seiden@linux.ibm.com> References: <20260831144802.834315-1-seiden@linux.ibm.com> <20260831144802.834315-24-seiden@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-GUID: rM4PDv8t8LtgoXWWsvkGxVtFUtq-EWVr X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTAzMDA3MyBTYWx0ZWRfX0qBnQykfpZag LyEzK0Q2M0otBgsmLVbuaAXKJ1SF9G5knSJd5e9TwSRJWnhgOAIKtus94XMVUFZbY3RAHtC2GFy GrJ/EQcRD6HLVB/I53AkO2OBxgHGDKhHPKzP43l2GO/48ztY7rAhh7v87gpdNIe5WDWhmkAJ+ps r4v5KU++n8/8KPATh3+9syWC4QpbkaMaOidSWFB3jSmFvZcc64ijxcRxh1oxIPWg7PTPyMNuszZ ArgyScowGdXwliSCGujAoDa30fmB3jZZcrv2wZffigtVL7djh0ln08kPoXM44OejTN/LYy91zMX Q09wpnUQlRpRCOIQ6R3mHs0FWFxpR436WNSLzGX4z3C/AjbFaUUH71G3nJ3MXzxkcqfqrk9/zLa FRaId3HgBwE7Ij5MeYY4GqvWtAsYZksNYqJyEtpqu6P3WRTDs+mdvIZFQOWdrCYOnIjrTmHt3Ib gswBu79IXXUSHWb+O3Q== X-Authority-Analysis: v=2.4 cv=Osl/DS/t c=1 sm=1 tr=0 ts=6a993229 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=kj9zAlcOel0A:10 a=VdqzKS8jKosA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=FnF-cwsuLINmlKs4EWIA:9 a=CjuIK1q_8ugA:10 X-Proofpoint-Spam-Info: AW1haW4tMjYwOTAzMDA3MyBTYWx0ZWRfX1y1xvG8KvX7m QIoVzvZSl28jyNFTawqLR78bFVRCcQlmevjvDeSlZNE3I7PMWOOiwILvshbzSvL0170u+/ERtyM +G6PSYLb8MF2/wG8GYXB8mQBExjwxiM= X-Proofpoint-ORIG-GUID: BC3K-qeP0r6HnRlADMcN-_W4aPty92j0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-09-03_02,2026-09-02_04,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 malwarescore=0 suspectscore=0 bulkscore=0 lowpriorityscore=0 adultscore=0 impostorscore=0 phishscore=0 clxscore=1015 priorityscore=1501 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2609030073 On Wed, Sep 02, 2026 at 09:20:23AM -0700, Sean Christopherson wrote: > On Mon, Aug 31, 2026, Steffen Eiden wrote: > > diff --git a/arch/s390/kvm/Kconfig b/arch/s390/kvm/Kconfig > > index 8d3ee17a1bcb..9c69ea16031e 100644 > > --- a/arch/s390/kvm/Kconfig > > +++ b/arch/s390/kvm/Kconfig > > @@ -53,4 +53,33 @@ config KVM_S390_UCONTROL > > > > If unsure, say N. > > > > +config KVM_S390_ARM64 > > + def_tristate y > > + prompt "KVM support for hardware accelerated arm64 guests" > > + depends on HAS_IOMEM > > + depends on KVM > > Is this actually necessary? I.e. does kvm.ko need to be *loaded* in order for > kvm-arm64.ko to be loaded? > > If kvm-arm64.ko does indeed have a hard dependency on kvm.ko, then I think it > makes sense to not have redundant "select" statements below. As an outsider, > it's super confusing because the KVM_S390_ARM64 are incomplete, e.g. are lacking > things like VIRT_XFER_TO_GUEST_WORK (at least, I assume those are lacking), and > makes it hard to see what is actually unique to kvm-arm64.ko. > > If kvm-arm64.ko doesn't have a dependency on kvm.ko, e.g. to initialize hardware > or something, then this "depends on" should go away. It is a bit more complicated unfortunately. KVM_S390_ARM64 depends on KVM as there is code around in the kernel & drivers (arch and common) which depends on CONFIG_KVM we need as well. I did not want to leak arch local configs to common code if I can avoid that. I could change it to select KVM ? Do you have another idea on how to solve this issue? The two modules are completely independent at compile and runtime. So kvm does not have to be loaded for kvm-arm64 to work. VIRT_XFER_TO_GUEST_WORK is only lacking for now. I will add it later. Currently the kvm-arm64 module is incomplete anyways but I did not want to send a 60+patches series and rather stage the introduction over multiple series. I will remove the duplicated config selections. Thanks for pointing it out. In previous series I had an explicit KVM_S390 config. Both KVM_S390 and KVM_ARM64 selected KVM. But this created too much churn around the whole tech-stack (default config change, s390 is the odd one out for the KVM config meaning, ...). Steffen