linux-kernel - Re: [PATCH 1/1] KVM: x86: to track if L1 is running L2 VM

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Date:   Sat, 6 Mar 2021 14:56:07 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Dongli Zhang <dongli.zhang@...cle.com>, x86@...nel.org,
        kvm@...r.kernel.org
Cc:     seanjc@...gle.com, vkuznets@...hat.com, wanpengli@...cent.com,
        jmattson@...gle.com, joro@...tes.org, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        linux-kernel@...r.kernel.org, joe.jin@...cle.com
Subject: Re: [PATCH 1/1] KVM: x86: to track if L1 is running L2 VM

On 05/03/21 23:57, Dongli Zhang wrote:
> The new per-cpu stat 'nested_run' is introduced in order to track if L1 VM
> is running or used to run L2 VM.
> 
> An example of the usage of 'nested_run' is to help the host administrator
> to easily track if any L1 VM is used to run L2 VM. Suppose there is issue
> that may happen with nested virtualization, the administrator will be able
> to easily narrow down and confirm if the issue is due to nested
> virtualization via 'nested_run'. For example, whether the fix like
> commit 88dddc11a8d6 ("KVM: nVMX: do not use dangling shadow VMCS after
> guest reset") is required.
> 
> Cc: Joe Jin <joe.jin@...cle.com>
> Signed-off-by: Dongli Zhang <dongli.zhang@...cle.com>
> ---
>   arch/x86/include/asm/kvm_host.h | 1 +
>   arch/x86/kvm/svm/nested.c       | 2 ++
>   arch/x86/kvm/vmx/nested.c       | 2 ++
>   arch/x86/kvm/x86.c              | 1 +
>   4 files changed, 6 insertions(+)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 877a4025d8da..7669215426ac 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1125,6 +1125,7 @@ struct kvm_vcpu_stat {
>   	u64 req_event;
>   	u64 halt_poll_success_ns;
>   	u64 halt_poll_fail_ns;
> +	u64 nested_run;
>   };
>   
>   struct x86_instruction_info;
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index 35891d9a1099..18c02e958a09 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -494,6 +494,8 @@ int nested_svm_vmrun(struct vcpu_svm *svm)
>   	struct kvm_host_map map;
>   	u64 vmcb12_gpa;
>   
> +	++svm->vcpu.stat.nested_run;
> +
>   	if (is_smm(&svm->vcpu)) {
>   		kvm_queue_exception(&svm->vcpu, UD_VECTOR);
>   		return 1;
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index bcca0b80e0d0..bd1343a0896e 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -3453,6 +3453,8 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)
>   	u32 interrupt_shadow = vmx_get_interrupt_shadow(vcpu);
>   	enum nested_evmptrld_status evmptrld_status;
>   
> +	++vcpu->stat.nested_run;
> +
>   	if (!nested_vmx_check_permission(vcpu))
>   		return 1;
>   
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 2a20ce60152e..f296febb0485 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -245,6 +245,7 @@ struct kvm_stats_debugfs_item debugfs_entries[] = {
>   	VCPU_STAT("l1d_flush", l1d_flush),
>   	VCPU_STAT("halt_poll_success_ns", halt_poll_success_ns),
>   	VCPU_STAT("halt_poll_fail_ns", halt_poll_fail_ns),
> +	VCPU_STAT("nested_run", nested_run),
>   	VM_STAT("mmu_shadow_zapped", mmu_shadow_zapped),
>   	VM_STAT("mmu_pte_write", mmu_pte_write),
>   	VM_STAT("mmu_pde_zapped", mmu_pde_zapped),
> 

Queued, thanks.

Paolo