Re: [PATCH v5 5/7] kvm, mem-hotplug: Reload L1's apic access page on migration when L2 is running.

Paolo Bonzini
2014-09-11T09:28:46Z

Il 11/09/2014 07:38, Tang Chen ha scritto:
> This patch only handle "L1 and L2 vm share one apic access page" situation.
>
> When L1 vm is running, if the shared apic access page is migrated, mmu_notifier will
> request all vcpus to exit to L0, and reload apic access page physical address for
> all the vcpus' vmcs (which is done by patch 5/6). And when it enters L2 vm, L2's vmcs
> will be updated in prepare_vmcs02() called by nested_vm_run(). So we need to do
> nothing.
>
> When L2 vm is running, if the shared apic access page is migrated, mmu_notifier will
> request all vcpus to exit to L0, and reload apic access page physical address for
> all L2 vmcs. And this patch requests apic access page reload in L2->L1 vmexit.
>
> Signed-off-by: Tang Chen <tangchen@cn.fujitsu.com>
> ---
> arch/x86/kvm/vmx.c | 7 +++++++
> virt/kvm/kvm_main.c | 1 +
> 2 files changed, 8 insertions(+)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index da6d55d..e7704b2 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -8796,6 +8796,13 @@ static void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason,
> }
>
> /*
> + * Do not call kvm_reload_apic_access_page() because we are now
> + * running, mmu_notifier will force to reload the page's hpa for L2
> + * vmcs. Need to reload it for L1 before entering L1.
> + */
> + kvm_reload_apic_access_page(vcpu->kvm);

That would kill performance for large L1 hosts.
vcpu_reload_apic_access_page should be enough (please rename it to
kvm_vcpu_reload_apic_access_page in patch 4, and export it).

Paolo

> + /*
> * Exiting from L2 to L1, we're now back to L1 which thinks it just
> * finished a VMLAUNCH or VMRESUME instruction, so we need to set the
> * success or failure flag accordingly.
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index d8280de..784127e 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -214,6 +214,7 @@ void kvm_reload_apic_access_page(struct kvm *kvm)
> {
> make_all_cpus_request(kvm, KVM_REQ_APIC_PAGE_RELOAD);
> }
> +EXPORT_SYMBOL_GPL(kvm_reload_apic_access_page);
>
> int kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id)
> {
>