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Date: Tue, 6 Sep 2022 15:25:57 -0700 From: Isaku Yamahata <isaku.yamahata@...il.com> To: Marc Zyngier <maz@...nel.org> Cc: isaku.yamahata@...el.com, linux-kernel@...r.kernel.org, kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>, Sean Christopherson <seanjc@...gle.com>, Thomas Gleixner <tglx@...utronix.de>, Will Deacon <will@...nel.org>, isaku.yamahata@...il.com, Kai Huang <kai.huang@...el.com>, Chao Gao <chao.gao@...el.com>, Atish Patra <atishp@...shpatra.org>, Shaokun Zhang <zhangshaokun@...ilicon.com>, John Garry <john.garry@...wei.com>, Daniel Lezcano <daniel.lezcano@...aro.org>, Huang Ying <ying.huang@...el.com>, Huacai Chen <chenhuacai@...nel.org>, Dave Hansen <dave.hansen@...ux.intel.com>, Borislav Petkov <bp@...en8.de> Subject: Re: [PATCH v3 00/22] KVM: hardware enable/disable reorganize On Mon, Sep 05, 2022 at 04:38:39PM +0100, Marc Zyngier <maz@...nel.org> wrote: > On Fri, 02 Sep 2022 03:17:35 +0100, > isaku.yamahata@...el.com wrote: > > > > From: Isaku Yamahata <isaku.yamahata@...el.com> > > > > Changes from v2: > > - Replace the first patch("KVM: x86: Drop kvm_user_return_msr_cpu_online()") > > with Sean's implementation > > - Included all patches of "Improve KVM's interaction with CPU hotplug" [2] > > Until v2, Tried to cherry-pick the least patches of it. It turned out that > > all the patches are desirable. > > > > This patch series is to implement the suggestion by Sean Christopherson [1] > > to reorganize enable/disable cpu virtualization feature by replacing > > the arch-generic current enable/disable logic with PM related hooks. And > > convert kvm/x86 to use new hooks. > > This series totally breaks on arm64 when playing with CPU hotplug. It > very much looks like preemption is now enabled in situations where we > don't expect it to (see below for the full-blown horror show). And > given the way it shows up in common code, I strongly suspect this > affects other architectures too. > > Note that if I only take patch #6 (with the subsequent fix that I > posted this morning), the system is perfectly happy with CPUs being > hotplugged on/off ad-nauseam. > Thanks for testing. As the discussion in 10/22, it seems like we need to relax the condition of WARN_ON or BUG_ON of preemptible(). Let me cook a version to relax it. -- Isaku Yamahata <isaku.yamahata@...il.com>
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