linux-kernel - Re: [PATCH v4 1/7] KVM: VMX: Introduce generic fastpath handler

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Message-ID: <87ees5f6gh.fsf@vitty.brq.redhat.com>
Date:   Thu, 30 Apr 2020 15:28:46 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Haiwei Li <lihaiwei@...cent.com>
Subject: Re: [PATCH v4 1/7] KVM: VMX: Introduce generic fastpath handler

Wanpeng Li <kernellwp@...il.com> writes:

> From: Wanpeng Li <wanpengli@...cent.com>
>
> Introduce generic fastpath handler to handle MSR fastpath, VMX-preemption
> timer fastpath etc, move it after vmx_complete_interrupts() in order that
> later patch can catch the case vmexit occurred while another event was
> being delivered to guest. There is no obversed performance difference for
> IPI fastpath testing after this move.
>
> Tested-by: Haiwei Li <lihaiwei@...cent.com>
> Cc: Haiwei Li <lihaiwei@...cent.com>
> Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 21 ++++++++++++++++-----
>  1 file changed, 16 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 3ab6ca6..9b5adb4 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -6583,6 +6583,20 @@ void vmx_update_host_rsp(struct vcpu_vmx *vmx, unsigned long host_rsp)
>  	}
>  }
>  
> +static enum exit_fastpath_completion vmx_exit_handlers_fastpath(struct kvm_vcpu *vcpu)
> +{
> +	if (!is_guest_mode(vcpu)) {

Nitpick: do we actually expect to have any fastpath handlers anytime
soon? If not, we could've written this as

	if (is_guest_mode(vcpu))
		return EXIT_FASTPATH_NONE;

and save on identation)

> +		switch (to_vmx(vcpu)->exit_reason) {
> +		case EXIT_REASON_MSR_WRITE:
> +			return handle_fastpath_set_msr_irqoff(vcpu);
> +		default:
> +			return EXIT_FASTPATH_NONE;
> +		}
> +	}
> +
> +	return EXIT_FASTPATH_NONE;
> +}
> +
>  bool __vmx_vcpu_run(struct vcpu_vmx *vmx, unsigned long *regs, bool launched);
>  
>  static enum exit_fastpath_completion vmx_vcpu_run(struct kvm_vcpu *vcpu)
> @@ -6757,17 +6771,14 @@ static enum exit_fastpath_completion vmx_vcpu_run(struct kvm_vcpu *vcpu)
>  	if (unlikely(vmx->exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY))
>  		return EXIT_FASTPATH_NONE;
>  
> -	if (!is_guest_mode(vcpu) && vmx->exit_reason == EXIT_REASON_MSR_WRITE)
> -		exit_fastpath = handle_fastpath_set_msr_irqoff(vcpu);
> -	else
> -		exit_fastpath = EXIT_FASTPATH_NONE;
> -
>  	vmx->loaded_vmcs->launched = 1;
>  	vmx->idt_vectoring_info = vmcs_read32(IDT_VECTORING_INFO_FIELD);
>  
>  	vmx_recover_nmi_blocking(vmx);
>  	vmx_complete_interrupts(vmx);
>  
> +	exit_fastpath = vmx_exit_handlers_fastpath(vcpu);
> +
>  	return exit_fastpath;
>  }

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>

-- 
Vitaly