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Wed, 14 Aug 2024 11:14:51 -0700 (PDT) X-Google-Smtp-Source: AGHT+IG6lRWgEY+GRw+Y2rxo2WrjU1gDgeDGJu9UBl9Icg/Y/Fj/LoEevNAbPFHDDVjcOvyablY/YQ== X-Received: by 2002:a05:600c:3b21:b0:426:6f87:65fc with SMTP id 5b1f17b1804b1-429dd23ce14mr30734045e9.17.1723659290916; Wed, 14 Aug 2024 11:14:50 -0700 (PDT) Received: from [192.168.10.47] ([151.95.101.29]) by smtp.googlemail.com with ESMTPSA id 5b1f17b1804b1-429ded582fcsm26990805e9.44.2024.08.14.11.14.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 14 Aug 2024 11:14:49 -0700 (PDT) Message-ID: Date: Wed, 14 Aug 2024 20:14:46 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 4/8] KVM: Add a module param to allow enabling virtualization when KVM is loaded To: Sean Christopherson Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Chao Gao , Kai Huang References: <20240608000639.3295768-1-seanjc@google.com> <20240608000639.3295768-5-seanjc@google.com> From: Paolo Bonzini Content-Language: en-US Autocrypt: addr=pbonzini@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 6/8/24 02:06, Sean Christopherson wrote: > Add an off-by-default module param, enable_virt_at_load, to let userspace > force virtualization to be enabled in hardware when KVM is initialized, > i.e. just before /dev/kvm is exposed to userspace. Enabling virtualization > during KVM initialization allows userspace to avoid the additional latency > when creating/destroying the first/last VM. Now that KVM uses the cpuhp > framework to do per-CPU enabling, the latency could be non-trivial as the > cpuhup bringup/teardown is serialized across CPUs, e.g. the latency could > be problematic for use case that need to spin up VMs quickly. > > Enabling virtualizaton during initialization will also allow KVM to setup > the Intel TDX Module, which requires VMX to be fully enabled, without > needing additional APIs to temporarily enable virtualization. > > Signed-off-by: Sean Christopherson I think we should enable it by default and wait for someone to complain. Or notice, even. Paolo > --- > virt/kvm/kvm_main.c | 37 +++++++++++++++++++++++++++++++++++++ > 1 file changed, 37 insertions(+) > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index 98e52d12f137..7bdd744e4821 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -5495,6 +5495,9 @@ static struct miscdevice kvm_dev = { > }; > > #ifdef CONFIG_KVM_GENERIC_HARDWARE_ENABLING > +static bool enable_virt_at_load; > +module_param(enable_virt_at_load, bool, 0444); > + > __visible bool kvm_rebooting; > EXPORT_SYMBOL_GPL(kvm_rebooting); > > @@ -5645,15 +5648,41 @@ static void kvm_disable_virtualization(void) > unregister_syscore_ops(&kvm_syscore_ops); > cpuhp_remove_state(CPUHP_AP_KVM_ONLINE); > } > + > +static int kvm_init_virtualization(void) > +{ > + if (enable_virt_at_load) > + return kvm_enable_virtualization(); > + > + return 0; > +} > + > +static void kvm_uninit_virtualization(void) > +{ > + if (enable_virt_at_load) > + kvm_disable_virtualization(); > + > + WARN_ON(kvm_usage_count); > +} > #else /* CONFIG_KVM_GENERIC_HARDWARE_ENABLING */ > static int kvm_enable_virtualization(void) > { > return 0; > } > > +static int kvm_init_virtualization(void) > +{ > + return 0; > +} > + > static void kvm_disable_virtualization(void) > { > > +} > + > +static void kvm_uninit_virtualization(void) > +{ > + > } > #endif /* CONFIG_KVM_GENERIC_HARDWARE_ENABLING */ > > @@ -6395,6 +6424,10 @@ int kvm_init(unsigned vcpu_size, unsigned vcpu_align, struct module *module) > > kvm_gmem_init(module); > > + r = kvm_init_virtualization(); > + if (r) > + goto err_virt; > + > /* > * Registration _must_ be the very last thing done, as this exposes > * /dev/kvm to userspace, i.e. all infrastructure must be setup! > @@ -6408,6 +6441,8 @@ int kvm_init(unsigned vcpu_size, unsigned vcpu_align, struct module *module) > return 0; > > err_register: > + kvm_uninit_virtualization(); > +err_virt: > kvm_vfio_ops_exit(); > err_vfio: > kvm_async_pf_deinit(); > @@ -6433,6 +6468,8 @@ void kvm_exit(void) > */ > misc_deregister(&kvm_dev); > > + kvm_uninit_virtualization(); > + > debugfs_remove_recursive(kvm_debugfs_dir); > for_each_possible_cpu(cpu) > free_cpumask_var(per_cpu(cpu_kick_mask, cpu));