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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id w25sm7281095edi.22.2021.09.20.11.22.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 20 Sep 2021 11:22:52 -0700 (PDT) To: Marc Zyngier Cc: Peter Zijlstra , Sean Christopherson , Ingo Molnar , Arnaldo Carvalho de Melo , Will Deacon , Mark Rutland , Catalin Marinas , Guo Ren , Nick Hu , Greentime Hu , Vincent Chen , Paul Walmsley , Palmer Dabbelt , Albert Ou , Thomas Gleixner , Borislav Petkov , x86@kernel.org, Boris Ostrovsky , Juergen Gross , Alexander Shishkin , Jiri Olsa , Namhyung Kim , James Morse , Alexandru Elisei , Suzuki K Poulose , "H. Peter Anvin" , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Stefano Stabellini , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-csky@vger.kernel.org, linux-riscv@lists.infradead.org, kvm@vger.kernel.org, xen-devel@lists.xenproject.org, Artem Kashkanov , Like Xu , Zhu Lingshan References: <20210828003558.713983-1-seanjc@google.com> <20210828201336.GD4353@worktop.programming.kicks-ass.net> <662e93f9-e858-689d-d203-742731ecad2c@redhat.com> <87tuifv3mb.wl-maz@kernel.org> <7a5825d1-d6e9-8ac8-5df2-cce693525da7@redhat.com> <87o88nuzzc.wl-maz@kernel.org> From: Paolo Bonzini Subject: Re: [PATCH v2 00/13] perf: KVM: Fix, optimize, and clean up callbacks Message-ID: <0eb2d4b1-23a4-c318-9f91-8dce78c6c8ad@redhat.com> Date: Mon, 20 Sep 2021 20:22:50 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <87o88nuzzc.wl-maz@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 20/09/21 15:40, Marc Zyngier wrote: >>> At least not before we >>> declare the arm64 single kernel image policy to be obsolete. >> >> --verbose please.:) I am sure you're right, but I don't understand >> the link between the two. > > To start making KVM/arm64 modular, you'd have to build it such as > there is no support for the nVHE hypervisor anymore. Which would mean > two different configs (one that can only work with VHE, and one for > the rest) and contradicts the current single kernel image policy. Ah okay, I interpreted the policy as "it's possible to build a single kernel image but it would be possible to build an image for a subset of the features as well". In that case you could have one config that can work either with or without VHE (and supports y/n) and one config that can only work with VHE (and supports y/m/n). The code to enter VHE EL2 would of course always be builtin. > It is bad enough that we have to support 3 sets of page sizes. > Doubling the validation space for the sake of being able to unload KVM > seems a dubious prospect. It's not even a configuration that matches kconfig very well, since it does have a way to build something *only as a module*, but not a way to build something only as built-in. That said, if you had the possibility to unload/reload KVM, you'll quickly become unable to live without it. :) Paolo