linux-kernel - Re: [PATCH] KVM: nVMX: consult PFER_MASK and PFER

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Date:   Mon, 24 Jul 2017 15:36:11 +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] KVM: nVMX: consult PFER_MASK and PFER_MATCH before nested
 vmexit if inject #PF

On 23/07/2017 03:05, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@...mail.com>
> 
> When generating #PF VM-exit, check equality:
> (PFEC & PFEC_MASK) == PFEC_MATCH
> If there is equality, the 14 bit of exception bitmap is used to take decision
> about generating #PF VM-exit. If there is inequality, inverted 14 bit is used.
> 
> Reported-by: Jim Mattson <jmattson@...gle.com>
> 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 | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 29fd8af..8a213f2 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -2429,6 +2429,8 @@ static void skip_emulated_instruction(struct kvm_vcpu *vcpu)
>  	vmx_set_interrupt_shadow(vcpu, 0);
>  }
>  
> +static bool nested_vmx_is_page_fault_vmexit(struct vmcs12 *vmcs12, u16 error_code);
> +
>  /*
>   * KVM wants to inject page-faults which it got to the guest. This function
>   * checks whether in a nested guest, we need to inject them to L1 or L2.
> @@ -2442,6 +2444,10 @@ static int nested_vmx_check_exception(struct kvm_vcpu *vcpu)
>  		(nr == PF_VECTOR && vcpu->arch.exception.nested_apf)))
>  		return 0;
>  
> +	if (nr == PF_VECTOR && !vcpu->arch.exception.nested_apf &&
> +		!nested_vmx_is_page_fault_vmexit(vmcs12, vcpu->arch.exception.error_code))
> +		return 0;

This is wrong, the check must replace "(vmcs12->exception_bitmap & (1u
<< nr)" if nr == PF_VECTOR.

Paolo

>  	if (vcpu->arch.exception.nested_apf) {
>  		vmcs_write32(VM_EXIT_INTR_ERROR_CODE, vcpu->arch.exception.error_code);
>  		nested_vmx_vmexit(vcpu, EXIT_REASON_EXCEPTION_NMI,
>