linux-kernel - Re: [PATCH 00/44] KVM: Rework kvm

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Message-ID: <Y2V1oslbw24/2Opd@google.com>
Date:   Fri, 4 Nov 2022 20:27:14 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Isaku Yamahata <isaku.yamahata@...il.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, Marc Zyngier <maz@...nel.org>,
        Huacai Chen <chenhuacai@...nel.org>,
        Aleksandar Markovic <aleksandar.qemu.devel@...il.com>,
        Anup Patel <anup@...infault.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        Eric Farman <farman@...ux.ibm.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Oliver Upton <oliver.upton@...ux.dev>,
        Atish Patra <atishp@...shpatra.org>,
        David Hildenbrand <david@...hat.com>, kvm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
        kvmarm@...ts.cs.columbia.edu, linux-mips@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, kvm-riscv@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Isaku Yamahata <isaku.yamahata@...el.com>,
        Fabiano Rosas <farosas@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Chao Gao <chao.gao@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Yuan Yao <yuan.yao@...el.com>
Subject: Re: [PATCH 00/44] KVM: Rework kvm_init() and hardware enabling

On Fri, Nov 04, 2022, Isaku Yamahata wrote:
> Thanks for the patch series. I the rebased TDX KVM patch series and it worked.
> Since cpu offline needs to be rejected in some cases(To keep at least one cpu
> on a package), arch hook for cpu offline is needed.

I hate to bring this up because I doubt there's a real use case for SUSPEND with
TDX, but the CPU offline path isn't just for true offlining of CPUs.  When the
system enters SUSPEND, only the initiating CPU goes through kvm_suspend()+kvm_resume(),
all responding CPUs go through CPU offline+online.  I.e. disallowing all CPUs from
going "offline" will prevent suspending the system.

I don't see anything in the TDX series or the specs that suggests suspend+resume
is disallowed when TDX is enabled, so blocking that seems just as wrong as
preventing software from soft-offlining CPUs.