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Message-ID: <1fd2e729-6e46-b0bf-d89e-f5d1b4dbde77@redhat.com>
Date:   Thu, 3 Nov 2022 18:57:55 +0100
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Subject: Re: [PATCH 36/44] KVM: x86: Do compatibility checks when onlining CPU
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To:     Sean Christopherson <seanjc@google.com>
Cc:     Marc Zyngier <maz@kernel.org>, Huacai Chen <chenhuacai@kernel.org>,
        Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>,
        Anup Patel <anup@brainfault.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Christian Borntraeger <borntraeger@linux.ibm.com>,
        Janosch Frank <frankja@linux.ibm.com>,
        Claudio Imbrenda <imbrenda@linux.ibm.com>,
        Matthew Rosato <mjrosato@linux.ibm.com>,
        Eric Farman <farman@linux.ibm.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        James Morse <james.morse@arm.com>,
        Alexandru Elisei <alexandru.elisei@arm.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Oliver Upton <oliver.upton@linux.dev>,
        Atish Patra <atishp@atishpatra.org>,
        David Hildenbrand <david@redhat.com>, kvm@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
        kvmarm@lists.cs.columbia.edu, linux-mips@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org, kvm-riscv@lists.infradead.org,
        linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Isaku Yamahata <isaku.yamahata@intel.com>,
        Fabiano Rosas <farosas@linux.ibm.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Chao Gao <chao.gao@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Yuan Yao <yuan.yao@intel.com>
References: <20221102231911.3107438-1-seanjc@google.com>
 <20221102231911.3107438-37-seanjc@google.com>
 <23bfd709-f99a-5a74-e4b9-1381b88453f1@redhat.com>
 <Y2P+E+631c0TNcK7@google.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
In-Reply-To: <Y2P+E+631c0TNcK7@google.com>
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On 11/3/22 18:44, Sean Christopherson wrote:
>>> Do compatibility checks when enabling hardware to effectively add
>>> compatibility checks when onlining a CPU.  Abort enabling, i.e. the
>>> online process, if the (hotplugged) CPU is incompatible with the known
>>> good setup.
>>
>> This paragraph is not true with this patch being before "KVM: Rename and
>> move CPUHP_AP_KVM_STARTING to ONLINE section".
>
> Argh, good eyes.  Getting the ordering correct in this series has been quite the
> struggle.  Assuming there are no subtle dependencies between x86 and common KVM,
> the ordering should be something like this:

It's not a problem to keep the ordering in this v1, just fix the commit 
message like "Do compatibility checks when enabling hardware to 
effectively add compatibility checks on CPU hotplug.  For now KVM is 
using a STARTING hook, which makes it impossible to abort the hotplug if 
the new CPU is incompatible with the known good setup; switching to an 
ONLINE hook will fix this."

Paolo

>    KVM: Opt out of generic hardware enabling on s390 and PPC
>    KVM: Register syscore (suspend/resume) ops early in kvm_init()
>    KVM: x86: Do compatibility checks when onlining CPU
>    KVM: SVM: Check for SVM support in CPU compatibility checks
>    KVM: VMX: Shuffle support checks and hardware enabling code around
>    KVM: x86: Do VMX/SVM support checks directly in vendor code
>    KVM: x86: Unify pr_fmt to use module name for all KVM modules
>    KVM: x86: Use KBUILD_MODNAME to specify vendor module name
>    KVM: Make hardware_enable_failed a local variable in the "enable all" path
>    KVM: Use a per-CPU variable to track which CPUs have enabled virtualization
>    KVM: Remove on_each_cpu(hardware_disable_nolock) in kvm_exit()
>    KVM: Drop kvm_count_lock and instead protect kvm_usage_count with kvm_lock
>    KVM: Disable CPU hotplug during hardware enabling
>    KVM: Rename and move CPUHP_AP_KVM_STARTING to ONLINE section
>    KVM: Drop kvm_arch_check_processor_compat() hook
>