linux-kernel - Re: [PATCH 03/10] KVM: nVMX: Pull exit_reason from vcpu_vmx in nested_vmx_exit

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Date:   Fri, 13 Mar 2020 13:38:37 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Xiaoyao Li <xiaoyao.li@...el.com>
Subject: Re: [PATCH 03/10] KVM: nVMX: Pull exit_reason from vcpu_vmx in nested_vmx_exit_reflected()

Sean Christopherson <sean.j.christopherson@...el.com> writes:

> Grab the exit reason from the vcpu struct in nested_vmx_exit_reflected()
> instead of having the exit reason explicitly passed from the caller.
> This fixes a discrepancy between VM-Fail and VM-Exit handling, as the
> VM-Fail case is already handled by checking vcpu_vmx, e.g. the exit
> reason previously passed on the stack is bogus if vmx->fail is set.

It's 0xdead, not bogus :-)

>
> Not taking the exit reason on the stack also avoids having to document
> that nested_vmx_exit_reflected() requires the full exit reason, as
> opposed to just the basic exit reason, which is not at all obvious since
> the only usage of the full exit reason is for tracing.
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/kvm/vmx/nested.c | 3 ++-
>  arch/x86/kvm/vmx/nested.h | 9 ++++-----
>  arch/x86/kvm/vmx/vmx.c    | 2 +-
>  3 files changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 79c7764c77b1..cb05bcbbfc4e 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -5518,11 +5518,12 @@ static bool nested_vmx_exit_handled_vmcs_access(struct kvm_vcpu *vcpu,
>   * should handle it ourselves in L0 (and then continue L2). Only call this
>   * when in is_guest_mode (L2).
>   */
> -bool nested_vmx_exit_reflected(struct kvm_vcpu *vcpu, u32 exit_reason)
> +bool nested_vmx_exit_reflected(struct kvm_vcpu *vcpu)
>  {
>  	u32 intr_info = vmcs_read32(VM_EXIT_INTR_INFO);
>  	struct vcpu_vmx *vmx = to_vmx(vcpu);
>  	struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
> +	u32 exit_reason = vmx->exit_reason;
>  
>  	if (vmx->nested.nested_run_pending)
>  		return false;
> diff --git a/arch/x86/kvm/vmx/nested.h b/arch/x86/kvm/vmx/nested.h
> index 8f5ff3e259c9..569cb828b6ca 100644
> --- a/arch/x86/kvm/vmx/nested.h
> +++ b/arch/x86/kvm/vmx/nested.h
> @@ -24,7 +24,7 @@ void nested_vmx_set_vmcs_shadowing_bitmap(void);
>  void nested_vmx_free_vcpu(struct kvm_vcpu *vcpu);
>  enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,
>  						     bool from_vmentry);
> -bool nested_vmx_exit_reflected(struct kvm_vcpu *vcpu, u32 exit_reason);
> +bool nested_vmx_exit_reflected(struct kvm_vcpu *vcpu);
>  void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason,
>  		       u32 exit_intr_info, unsigned long exit_qualification);
>  void nested_sync_vmcs12_to_shadow(struct kvm_vcpu *vcpu);
> @@ -75,12 +75,11 @@ static inline bool nested_ept_ad_enabled(struct kvm_vcpu *vcpu)
>   * Conditionally reflect a VM-Exit into L1.  Returns %true if the VM-Exit was
>   * reflected into L1.
>   */
> -static inline bool nested_vmx_reflect_vmexit(struct kvm_vcpu *vcpu,
> -					     u32 exit_reason)
> +static inline bool nested_vmx_reflect_vmexit(struct kvm_vcpu *vcpu)
>  {
>  	u32 exit_intr_info;
>  
> -	if (!nested_vmx_exit_reflected(vcpu, exit_reason))
> +	if (!nested_vmx_exit_reflected(vcpu))
>  		return false;
>  
>  	/*
> @@ -99,7 +98,7 @@ static inline bool nested_vmx_reflect_vmexit(struct kvm_vcpu *vcpu,
>  			vmcs_read32(VM_EXIT_INTR_ERROR_CODE);
>  	}
>  
> -	nested_vmx_vmexit(vcpu, exit_reason, exit_intr_info,
> +	nested_vmx_vmexit(vcpu, to_vmx(vcpu)->exit_reason, exit_intr_info,
>  			  vmcs_readl(EXIT_QUALIFICATION));
>  	return true;
>  }
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index c1caac7e8f57..c7715c880ea7 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -5863,7 +5863,7 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu,
>  	if (vmx->emulation_required)
>  		return handle_invalid_guest_state(vcpu);
>  
> -	if (is_guest_mode(vcpu) && nested_vmx_reflect_vmexit(vcpu, exit_reason))
> +	if (is_guest_mode(vcpu) && nested_vmx_reflect_vmexit(vcpu))
>  		return 1;
>  
>  	if (exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY) {

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

-- 
Vitaly