linux-kernel - Re: [PATCH v3 3/6] KVM: MMU: make return value of mmio page fault handler more readable

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Date:	Mon, 10 Jun 2013 10:57:50 +0300
From:	Gleb Natapov <gleb@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Cc:	avi.kivity@...il.com, mtosatti@...hat.com, pbonzini@...hat.com,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v3 3/6] KVM: MMU: make return value of mmio page fault
 handler more readable

On Fri, Jun 07, 2013 at 04:51:25PM +0800, Xiao Guangrong wrote:
> Define some meaningful names instead of raw code
> 
> Signed-off-by: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
> ---
>  arch/x86/kvm/mmu.c | 15 +++++----------
>  arch/x86/kvm/mmu.h | 14 ++++++++++++++
>  arch/x86/kvm/vmx.c |  4 ++--
>  3 files changed, 21 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index eca91bd..044d8c0 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -3222,17 +3222,12 @@ static u64 walk_shadow_page_get_mmio_spte(struct kvm_vcpu *vcpu, u64 addr)
>  	return spte;
>  }
>  
> -/*
> - * If it is a real mmio page fault, return 1 and emulat the instruction
> - * directly, return 0 to let CPU fault again on the address, -1 is
> - * returned if bug is detected.
> - */
>  int handle_mmio_page_fault_common(struct kvm_vcpu *vcpu, u64 addr, bool direct)
>  {
>  	u64 spte;
>  
>  	if (quickly_check_mmio_pf(vcpu, addr, direct))
> -		return 1;
> +		return RET_MMIO_PF_EMULATE;
>  
>  	spte = walk_shadow_page_get_mmio_spte(vcpu, addr);
>  
> @@ -3245,7 +3240,7 @@ int handle_mmio_page_fault_common(struct kvm_vcpu *vcpu, u64 addr, bool direct)
>  
>  		trace_handle_mmio_page_fault(addr, gfn, access);
>  		vcpu_cache_mmio_info(vcpu, addr, gfn, access);
> -		return 1;
> +		return RET_MMIO_PF_EMULATE;
>  	}
>  
>  	/*
> @@ -3253,13 +3248,13 @@ int handle_mmio_page_fault_common(struct kvm_vcpu *vcpu, u64 addr, bool direct)
>  	 * it's a BUG if the gfn is not a mmio page.
>  	 */
>  	if (direct && !check_direct_spte_mmio_pf(spte))
> -		return -1;
> +		return RET_MMIO_PF_BUG;
>  
>  	/*
>  	 * If the page table is zapped by other cpus, let CPU fault again on
>  	 * the address.
>  	 */
> -	return 0;
> +	return RET_MMIO_PF_RETRY;
>  }
>  EXPORT_SYMBOL_GPL(handle_mmio_page_fault_common);
>  
> @@ -3269,7 +3264,7 @@ static int handle_mmio_page_fault(struct kvm_vcpu *vcpu, u64 addr,
>  	int ret;
>  
>  	ret = handle_mmio_page_fault_common(vcpu, addr, direct);
> -	WARN_ON(ret < 0);
> +	WARN_ON(ret == RET_MMIO_PF_BUG);
>  	return ret;
>  }
>  
> diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
> index 922bfae..ba6a19c 100644
> --- a/arch/x86/kvm/mmu.h
> +++ b/arch/x86/kvm/mmu.h
> @@ -52,6 +52,20 @@
>  
>  int kvm_mmu_get_spte_hierarchy(struct kvm_vcpu *vcpu, u64 addr, u64 sptes[4]);
>  void kvm_mmu_set_mmio_spte_mask(u64 mmio_mask);
> +
> +/*
> + * Return values of handle_mmio_page_fault_common:
> + * RET_MMIO_PF_EMULATE: it is a real mmio page fault, emulate the instruction
> + *			 directly.
> + * RET_MMIO_PF_RETRY: let CPU fault again on the address.
> + * RET_MMIO_PF_BUG: bug is detected.
> + */
> +enum {
> +	RET_MMIO_PF_EMULATE = 1,
> +	RET_MMIO_PF_RETRY = 0,
> +	RET_MMIO_PF_BUG = -1
> +};
I would order them from -1 to 1 and rename RET_MMIO_PF_BUG to
RET_MMIO_PF_ERROR, but no need to resend just for that.

> +
>  int handle_mmio_page_fault_common(struct kvm_vcpu *vcpu, u64 addr, bool direct);
>  int kvm_init_shadow_mmu(struct kvm_vcpu *vcpu, struct kvm_mmu *context);
>  
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 78ee123..85c8d51 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -5366,10 +5366,10 @@ static int handle_ept_misconfig(struct kvm_vcpu *vcpu)
>  	gpa = vmcs_read64(GUEST_PHYSICAL_ADDRESS);
>  
>  	ret = handle_mmio_page_fault_common(vcpu, gpa, true);
> -	if (likely(ret == 1))
> +	if (likely(ret == RET_MMIO_PF_EMULATE))
>  		return x86_emulate_instruction(vcpu, gpa, 0, NULL, 0) ==
>  					      EMULATE_DONE;
> -	if (unlikely(!ret))
> +	if (unlikely(ret == RET_MMIO_PF_RETRY))
>  		return 1;
>  
>  	/* It is the real ept misconfig */
> -- 
> 1.8.1.4

--
			Gleb.
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