linux-kernel - Re: [PATCH v5 2/4] KVM: async_pf: Add L1 guest async

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Date:   Tue, 27 Jun 2017 15:30:49 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [PATCH v5 2/4] KVM: async_pf: Add L1 guest async_pf #PF vmexit
 handler



On 27/06/2017 03:46, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@...mail.com>
> 
> This patch adds the L1 guest async page fault #PF vmexit handler, such
> #PF is converted into vmexit from L2 to L1 on #PF which is then handled
> by L1 similar to ordinary async page fault.
> 
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Radim Krčmář <rkrcmar@...hat.com>
> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
> ---
>  arch/x86/kvm/vmx.c | 34 ++++++++++++++++++++++++++++------
>  1 file changed, 28 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index df825bb..f533cc1 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -616,6 +616,7 @@ struct vcpu_vmx {
>  	bool emulation_required;
>  
>  	u32 exit_reason;
> +	u32 apf_reason;

Can you instead of move vcpu_svm's apf_reason field to kvm_vcpu_arch?
(e.g. vcpu->arch.apf.host_apf_reason)?

>  	/* Posted interrupt descriptor */
>  	struct pi_desc pi_desc;
> @@ -5648,14 +5649,31 @@ static int handle_exception(struct kvm_vcpu *vcpu)
>  	}
>  
>  	if (is_page_fault(intr_info)) {
> -		/* EPT won't cause page fault directly */
> -		BUG_ON(enable_ept);
>  		cr2 = vmcs_readl(EXIT_QUALIFICATION);
> -		trace_kvm_page_fault(cr2, error_code);
> +		switch (vmx->apf_reason) {
> +		default:
> +			/* EPT won't cause page fault directly */
> +			BUG_ON(enable_ept);
> +			trace_kvm_page_fault(cr2, error_code);
>  
> -		if (kvm_event_needs_reinjection(vcpu))
> -			kvm_mmu_unprotect_page_virt(vcpu, cr2);
> -		return kvm_mmu_page_fault(vcpu, cr2, error_code, NULL, 0);
> +			if (kvm_event_needs_reinjection(vcpu))
> +				kvm_mmu_unprotect_page_virt(vcpu, cr2);
> +			return kvm_mmu_page_fault(vcpu, cr2, error_code, NULL, 0);
> +			break;
> +		case KVM_PV_REASON_PAGE_NOT_PRESENT:
> +			vmx->apf_reason = 0;
> +			local_irq_disable();
> +			kvm_async_pf_task_wait(cr2);
> +			local_irq_enable();
> +			break;
> +		case KVM_PV_REASON_PAGE_READY:
> +			vmx->apf_reason = 0;
> +			local_irq_disable();
> +			kvm_async_pf_task_wake(cr2);
> +			local_irq_enable();
> +			break;
> +		}
> +		return 0;
>  	}


This code can be moved to a common function

	int kvm_handle_page_fault(struct kvm_vcpu *vcpu, u64 error_code,
				  u64 fault_address);

in mmu.c.  It can be used by vmx.c here and in svm.c's pf_interception.

You can change "enable_ept" to "tdp_enabled" (but please make that a
WARN_ON_ONCE, too).

Thanks,

Paolo