linux-kernel - Re: [PATCH v3 00/22] KVM: hardware enable/disable reorganize

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Message-ID: <20220906222557.GB443010@ls.amr.corp.intel.com>
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>