linux-kernel - Re: [PATCH v5 00/30] KVM: hardware enable/disable reorganize

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Message-ID: <Y0da+Sj3BjYnMoh3@google.com>
Date:   Thu, 13 Oct 2022 00:25:29 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     isaku.yamahata@...el.com
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>, 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>,
        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 v5 00/30] KVM: hardware enable/disable reorganize

On Thu, Sep 22, 2022, isaku.yamahata@...el.com wrote:
> From: Isaku Yamahata <isaku.yamahata@...el.com>
> 
> 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.

Thanks for putting this together, actually seeing code is super helpful!

Unfortunately, after seeing the code, I think my suggestion was a bad one.  At
the end of this series, there's a rather gross amount of duplicate code between
x86 and common KVM, and no clear line of sight to improving things.

Even if we move ARM, s390, and PPC away from the generic hooks, MIPS and RISC-V
still need the generic implementation, i.e. we'll still have duplicate code.

Rather than force arch code to implement most/all power management hooks, I think
we can achieve a similar outcome (let ARM do its own thing, turn s390 and PPC into
nops) by wrapping the hardware enable/disable (and thus PM code) in a Kconfig,
e.g. KVM_GENERIC_HARDWARE_ENABLING.

I'll throw together a rough prototype tomorrow (got partway through and then got
distracted by other stuff) and hopefully post an RFC series.

Thanks again!