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Wed, 2 Sep 2026 08:22:58 +0000 (GMT) Date: Wed, 2 Sep 2026 10:22:56 +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 03/23] KVM: Allow KVM implementations to switch off MMIO independent of Kconfig Message-ID: <20260902082256.438647-A-seiden@linux.ibm.com> References: <20260831144802.834315-1-seiden@linux.ibm.com> <20260831144802.834315-4-seiden@linux.ibm.com> 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: PegjYO2dcjjFja5IBSIoksPFsA3_yCIF X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTAyMDA3MCBTYWx0ZWRfXxZTpdKIMadP+ hECdMkWYg8VeNfu0AcnLQXTBiCaI3zlfwxdL45awk2mKQnlMZxXf6EFh7Hspz115kooBrW+gcWo OLyn7miU1JZqbCSMrxUTfW6vWd5WJw7XxLwJ9DFUxT6X7tS8aj+fr/VPIozvNYDtFSLI/4mqIs8 nH9zyZd9ioK0Rck+6/+u7Tsqzu9J2cct+H3U1UFdbKSaZxg2UDfw/Glkl2jSmh6vKysF6LgWpw2 Lq2pOvvMnO0BpiJcccPT5tiNjkvggdSdGlBCeveoRG9rKL3guNZmvX6vLc7sXsZ4wyi98BmohuF D03m3V4Hl6nCl2yRfSAmBhYDASoSrgySjQ9gsH9+KEtgiT2aasUIM4lG9+dEe4URedrlOiR+g5j 43ltPF+D7gKfIlc9Ahlou/LUrwHp3qR8j2fnRx8mYClkC9PppYhB9FJRs+LCiaJGtXAZLcPRHdi ijk/UHb3RV6yP45ktwg== X-Proofpoint-ORIG-GUID: Z9gBGfJv4YrXzi45b0jSQ8_rbtmzd5ws X-Proofpoint-Spam-Info: AW1haW4tMjYwOTAyMDA3MCBTYWx0ZWRfX1eINHSzT2ujO TH6kMMJZ9sI97OOY17eJfPQkbahQxVxIlkGHm4vD+RnzUngsAZ2wsqanN1WuzTeJeLdlLVCMN7W 1cmBj4yRXW+6VJ7qNEODiTYVaqbQMps= X-Authority-Analysis: v=2.4 cv=B92JFutM c=1 sm=1 tr=0 ts=6a97dce7 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=kj9zAlcOel0A:10 a=VdqzKS8jKosA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=VwQbUJbxAAAA:8 a=LZd3j2bqb7V-iaZHDUcA:9 a=CjuIK1q_8ugA: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=2026-09-02_01,2026-09-01_03,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 spamscore=0 clxscore=1015 suspectscore=0 phishscore=0 lowpriorityscore=0 bulkscore=0 priorityscore=1501 impostorscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2609020070 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260902_012316_546576_1B92C31E X-CRM114-Status: GOOD ( 19.77 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Sep 01, 2026 at 05:38:53PM -0700, Sean Christopherson wrote: > On Mon, Aug 31, 2026, Steffen Eiden wrote: > > Only defining KVM_MMIO is not flexible enough for multi-KVM systems > > where one KVM implements MMIO but others do not. Solve this by > > additionally testing for the non-existence of KVM_NO_MMIO before > > including MMIO code to KVM. > > Ewwwww. IIUC, s390 ends up with two KVM modules, i.e. there really are two different > KVMs being built. Rather than have a KVM_MMIO and NO_KVM_MMIO, I vote very > strongly to drop CONFIG_KVM_MMIO entirely and replace it with __KVM_HAVE_ARCH_MMIO, > a la __KVM_HAVE_ARCH_VM_FREE and others. Tracking two separate macros is going > to be annoying to maintain, and will definitely be confusing for non-s390 people. You understand correclty we compile kvm twice into different modules. I already did this approach (with a differnt name) and dropped the config in (v1,v2,v3, and) v4 of this Series[1] and Marc voted against this :) I have no strong opinion on this and do whatever the both of you come up with :) > > It'll mean linking in an emtpy coalesced_mmio.o on s390 when building without arm64 > support, but I'm guessing that won't be at all common for s390 builds. This should be no problem, I assume. Steffen [1] https://lore.kernel.org/all/87a4s37scc.wl-maz@kernel.org/