linux-kernel - Re: [PATCH v5 3/7] kvm: Make init_rmode_identity

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Date:	Thu, 11 Sep 2014 11:17:31 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Tang Chen <tangchen@...fujitsu.com>, gleb@...nel.org,
	mtosatti@...hat.com, nadav.amit@...il.com, jan.kiszka@....de
CC:	kvm@...r.kernel.org, laijs@...fujitsu.com,
	isimatu.yasuaki@...fujitsu.com, guz.fnst@...fujitsu.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 3/7] kvm: Make init_rmode_identity_map() return 0 on
 success.

Il 11/09/2014 07:38, Tang Chen ha scritto:
> In init_rmode_identity_map(), there two variables indicating the return
> value, r and ret, and it return 0 on error, 1 on success. The function
> is only called by vmx_create_vcpu(), and r is redundant.
> 
> This patch removes the redundant variable r, and make init_rmode_identity_map()
> return 0 on success, -errno on failure.
> 
> Signed-off-by: Tang Chen <tangchen@...fujitsu.com>
> ---
>  arch/x86/kvm/vmx.c | 25 +++++++++++--------------
>  1 file changed, 11 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 953d529..63c4c3e 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -3939,45 +3939,42 @@ out:
>  
>  static int init_rmode_identity_map(struct kvm *kvm)
>  {
> -	int i, idx, r, ret = 0;
> +	int i, idx, ret = 0;
>  	pfn_t identity_map_pfn;
>  	u32 tmp;
>  
>  	if (!enable_ept)
> -		return 1;
> +		return 0;
>  
>  	/* Protect kvm->arch.ept_identity_pagetable_done. */
>  	mutex_lock(&kvm->slots_lock);
>  
> -	if (likely(kvm->arch.ept_identity_pagetable_done)) {
> -		ret = 1;
> +	if (likely(kvm->arch.ept_identity_pagetable_done))
>  		goto out2;
> -	}
>  
>  	identity_map_pfn = kvm->arch.ept_identity_map_addr >> PAGE_SHIFT;
>  
> -	r = alloc_identity_pagetable(kvm);
> -	if (r)
> +	ret = alloc_identity_pagetable(kvm);
> +	if (ret)
>  		goto out2;
>  
>  	idx = srcu_read_lock(&kvm->srcu);
> -	r = kvm_clear_guest_page(kvm, identity_map_pfn, 0, PAGE_SIZE);
> -	if (r < 0)
> +	ret = kvm_clear_guest_page(kvm, identity_map_pfn, 0, PAGE_SIZE);
> +	if (ret)
>  		goto out;
>  	/* Set up identity-mapping pagetable for EPT in real mode */
>  	for (i = 0; i < PT32_ENT_PER_PAGE; i++) {
>  		tmp = (i << 22) + (_PAGE_PRESENT | _PAGE_RW | _PAGE_USER |
>  			_PAGE_ACCESSED | _PAGE_DIRTY | _PAGE_PSE);
> -		r = kvm_write_guest_page(kvm, identity_map_pfn,
> +		ret = kvm_write_guest_page(kvm, identity_map_pfn,
>  				&tmp, i * sizeof(tmp), sizeof(tmp));
> -		if (r < 0)
> +		if (ret)
>  			goto out;
>  	}
>  	kvm->arch.ept_identity_pagetable_done = true;
> -	ret = 1;
> +
>  out:
>  	srcu_read_unlock(&kvm->srcu, idx);
> -
>  out2:
>  	mutex_unlock(&kvm->slots_lock);
>  	return ret;
> @@ -7645,7 +7642,7 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
>  			kvm->arch.ept_identity_map_addr =
>  				VMX_EPT_IDENTITY_PAGETABLE_ADDR;
>  		err = -ENOMEM;
> -		if (!init_rmode_identity_map(kvm))
> +		if (init_rmode_identity_map(kvm))

Please add "< 0" here.  I would also consider setting err to the return
value of init_rmode_identity_map, and initializing it to -ENOMEM only
after the "if".

Paolo

>  			goto free_vmcs;

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