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Thu, 17 Sep 2026 11:07:47 +0000 (GMT) Received: from [9.224.77.173] (unknown [9.224.77.173]) by smtpav03.fra02v.mail.ibm.com (Postfix) with ESMTP; Thu, 17 Sep 2026 11:07:47 +0000 (GMT) Message-ID: <51286424-e802-4ea9-b958-925fee8025ed@linux.ibm.com> Date: Thu, 17 Sep 2026 13:07:47 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 23/23] KVM: s390: arm64: Add KVM_S390_ARM64 Kconfig and Makefile To: Sean Christopherson , Steffen Eiden 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 , 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 References: <20260831144802.834315-1-seiden@linux.ibm.com> <20260831144802.834315-24-seiden@linux.ibm.com> <20260903083857.33034-B-seiden@linux.ibm.com> <20260903154317.246414-A-seiden@linux.ibm.com> Content-Language: en-US From: Christian Borntraeger In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-Spam-Info: AW1haW4tMjYwOTE3MDE1MyBTYWx0ZWRfXxvXgm8oqRp19 nQrhg9EQ/0iT2IXEFt08BHaHhUsgrKyvoPi+NFAeU3UU5WQjtMwZp8b7tXugIn2k7CFo6eFSYwM tQwG/muNP2QjgP5jk4v4+zXUwT3/rLA= X-Proofpoint-ORIG-GUID: 6Ugh16w0kSKYc6k82HwIr7iH6p4aBU1L X-Proofpoint-GUID: pYhdyPFgJVLZ4pZZ3Lh06XuplLJMgZjH X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTE3MDE1MyBTYWx0ZWRfX/J3l0K/K4T4/ k1Qu9iTB8gKSi3qzkVLZPgP5TuALabaJDnd0MM3f5Gfs6A3UuW2z5HRDT37VSdiByJGRkKXsnt/ XOynhvAAg3kUEdrZQAY9MefMR0mynOoSp0QD+EiQJsNr8q3FYo0H2f9/gwmBogBuA7yIZWL7vXa 2OdgbCkRNP6cGH52IOdVvccZYRJr+ZGXqtsHoQzsIKw0y06Uxy20/0kbI6c71TV/3pkRUS/xPpp aYFNvov7S/8RkhmCAX8Wd5caY/2pU2zltPV9DvQjkG3v1RUDfNSlPLSdq+i19bOaDJ3R7dbeZGJ a2XzEvBlGSfRqWfT3/Yytvo4VkqO6/KSzA0ca6GBLbLuLDPYODZTwW1N+kLnoXRCKAtTK3Ari4L Boxt4IoBYN6InRSXQuM1d7iJT+Gsl0k1gKTlXbDsX+JifTUSAMxeYELUMQKy9/uWQw77Vpwc87J J/UxAnI0um8eOvNI4wg== X-Authority-Analysis: v=2.4 cv=F+7C5ahN c=1 sm=1 tr=0 ts=6aabca0a cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=IkcTkHD0fZMA:10 a=VdqzKS8jKosA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=nRLfC78URy_-QQUzUV8A:9 a=QEXdDO2ut3YA:10 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=2026-09-17_02,2026-09-16_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 suspectscore=0 phishscore=0 clxscore=1011 malwarescore=0 lowpriorityscore=0 bulkscore=0 spamscore=0 impostorscore=0 adultscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2609040000 definitions=main-2609170153 Am 03.09.26 um 18:33 schrieb Sean Christopherson: > On Thu, Sep 03, 2026, Steffen Eiden wrote: >> On Thu, Sep 03, 2026 at 07:43:58AM -0700, Sean Christopherson wrote: >>> And FWIW, while it might seem daunting, from my perspective it's not actually that >>> much churn to do things "right". Provide KVM_S390_NATIVE, and then have KVM reflect >>> the "weakest" of S390_NATIVE vs. S390_ARCH. I.e. make KVM=m if either of the "real" >>> KVMs will be a module. That requires some creative shenanigans, but it's not hard, >>> just weird. >> >> FYI the first versions of this series had a 3 configs approach very >> similar to yours. >> >> IIRC it was not so much the churn we have in (upstream) kernel code but >> more on the distro side and to everyone building the kernel in their >> favourite architecture (s390 :)) > > How many people are running distro kernels on s390 hardware? And how many distros > actually change the default KVM settings, e.g. to build KVM as a module instead of > baking it into the kernel? My guess is "not many" and "almost none", i.e. the > actual impact on downstream users is likely miniscule. > >> Suddenly the KVM config changed its behaviour (effectively becoming a noop) > > Not really, because "KVM" itself is inaccessible (well, unless someone is hand- > editing .configs or generating them by script, but that's their own fault). > E.g. upgrading to a new kernel will explicitly prompt the user to choose for both > KVM_S390_NATIVE and KVM_S390_ARM64 (or whatever they get called). > >> I am starting to think that having no separate config option for arm on >> s390 might be the easisest way. Just KVM and guard both modules behind >> it. It reduces the config space bloat and I do not see a reason why somoeone >> should only compile one KVM module but not the other. kvm-arm64 won't >> load if you do not have the hardware anyways. > > Because there may be an unforseen need down the road? Smushing things together > after the fact is generally easy, pulling things apart without breaking everything > is usually much, much harder. > >> But I am not opposed to the x86 approach. Just thinking loud. >> >> Anyways, I am off for vacation expect a reduced reply frequency from my >> side :) Yet another option I think there is value in keeping the config space simpte for users. Why not simply keep CONFIG_KVM and it will disable, module build, compile-in both variants.