linux-kernel - Re: [PATCH v6 5/6] kvm, mem-hotplug: Reload L1's apic access page on migration when L2 is running.

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Date:	Tue, 16 Sep 2014 13:34:46 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Tang Chen <tangchen@...fujitsu.com>, gleb@...nel.org,
	mtosatti@...hat.com, nadav.amit@...il.com, jan.kiszka@....de
CC:	kvm@...r.kernel.org, laijs@...fujitsu.com,
	isimatu.yasuaki@...fujitsu.com, guz.fnst@...fujitsu.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 5/6] kvm, mem-hotplug: Reload L1's apic access page
 on migration when L2 is running.

Il 16/09/2014 12:42, 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@...fujitsu.com>

But if kvm_vcpu_reload_apic_access_page is called when the active VMCS
is a VMCS02, the APIC access address will be corrupted, no?

So, even if you are not touching the pages pinned by nested virt, you
need an

   if (!is_guest_mode(vcpu) ||
       !(vmx->nested.current_vmcs12->secondary_vm_exec_control &
         SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES))

as suggested by Gleb in the review of v5.

Paolo

> ---
>  arch/x86/include/asm/kvm_host.h | 1 +
>  arch/x86/kvm/vmx.c              | 6 ++++++
>  arch/x86/kvm/x86.c              | 3 ++-
>  3 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 514183e..92b3e72 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1046,6 +1046,7 @@ int kvm_cpu_has_interrupt(struct kvm_vcpu *vcpu);
>  int kvm_arch_interrupt_allowed(struct kvm_vcpu *vcpu);
>  int kvm_cpu_get_interrupt(struct kvm_vcpu *v);
>  void kvm_vcpu_reset(struct kvm_vcpu *vcpu);
> +void kvm_vcpu_reload_apic_access_page(struct kvm_vcpu *vcpu);
>  
>  void kvm_define_shared_msr(unsigned index, u32 msr);
>  void kvm_set_shared_msr(unsigned index, u64 val, u64 mask);
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index a1a9797..d0d5981 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -8795,6 +8795,12 @@ static void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason,
>  	}
>  
>  	/*
> +	 * We are now running in L2, mmu_notifier will force to reload the
> +	 * page's hpa for L2 vmcs. Need to reload it for L1 before entering L1.
> +	 */
> +	kvm_vcpu_reload_apic_access_page(vcpu);
> +
> +	/*
>  	 * 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/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 27c3d30..3f458b2 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5989,7 +5989,7 @@ static void vcpu_scan_ioapic(struct kvm_vcpu *vcpu)
>  	kvm_apic_update_tmr(vcpu, tmr);
>  }
>  
> -static void kvm_vcpu_reload_apic_access_page(struct kvm_vcpu *vcpu)
> +void kvm_vcpu_reload_apic_access_page(struct kvm_vcpu *vcpu)
>  {
>  	/*
>  	 * apic access page could be migrated. When the page is being migrated,
> @@ -6001,6 +6001,7 @@ static void kvm_vcpu_reload_apic_access_page(struct kvm_vcpu *vcpu)
>  	kvm_x86_ops->set_apic_access_page_addr(vcpu->kvm,
>  				page_to_phys(vcpu->kvm->arch.apic_access_page));
>  }
> +EXPORT_SYMBOL_GPL(kvm_vcpu_reload_apic_access_page);
>  
>  /*
>   * Returns 1 to let __vcpu_run() continue the guest execution loop without
> 

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