linux-kernel - Re: [PATCH 1/4] KVM: MMU: fix permission

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Date:	Fri, 25 Mar 2016 14:35:03 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Xiao Guangrong <guangrong.xiao@...ux.intel.com>
Cc:	gleb@...nel.org, mtosatti@...hat.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] KVM: MMU: fix permission_fault()



On 25/03/2016 14:19, Xiao Guangrong wrote:
> kvm-unit-tests complained about the PFEC is not set properly, e.g,:
> test pte.rw pte.d pte.nx pde.p pde.rw pde.pse user fetch: FAIL: error code 15 
> expected 5
> Dump mapping: address: 0x123400000000
> ------L4: 3e95007
> ------L3: 3e96007
> ------L2: 2000083

What's the command line for the reproducer?

> diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
> index b70df72..81bffd1 100644
> --- a/arch/x86/kvm/mmu.h
> +++ b/arch/x86/kvm/mmu.h
> @@ -154,7 +154,7 @@ static inline u8 permission_fault(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
>  				  unsigned pfec)
>  {
>  	int cpl = kvm_x86_ops->get_cpl(vcpu);
> -	unsigned long rflags = kvm_x86_ops->get_rflags(vcpu);
> +	unsigned long errcode, rflags = kvm_x86_ops->get_rflags(vcpu);
>  
>  	/*
>  	 * If CPL < 3, SMAP prevention are disabled if EFLAGS.AC = 1.
> @@ -175,7 +175,7 @@ static inline u8 permission_fault(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
>  	bool fault = (mmu->permissions[index] >> pte_access) & 1;
>  
>  	WARN_ON(pfec & (PFERR_PK_MASK | PFERR_RSVD_MASK));
> -	pfec |= PFERR_PRESENT_MASK;
> +	errcode = PFERR_PRESENT_MASK;

So is this patch doing the same as "KVM: MMU: precompute page fault
error code"?  It was necessary after all. :)

Paolo

>  
>  	if (unlikely(mmu->pkru_mask)) {
>  		u32 pkru_bits, offset;
> @@ -193,11 +193,11 @@ static inline u8 permission_fault(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
>  			((pte_access & PT_USER_MASK) << (PFERR_RSVD_BIT - PT_USER_SHIFT));
>  
>  		pkru_bits &= mmu->pkru_mask >> offset;
> -		pfec |= -pkru_bits & PFERR_PK_MASK;
> +		errcode |= -pkru_bits & PFERR_PK_MASK;
>  		fault |= (pkru_bits != 0);
>  	}
>  
> -	return -(uint32_t)fault & pfec;
> +	return -(uint32_t)fault & errcode;
>  }
>  
>  void kvm_mmu_invalidate_zap_all_pages(struct kvm *kvm);
> diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
> index 1d971c7..bc019f7 100644
> --- a/arch/x86/kvm/paging_tmpl.h
> +++ b/arch/x86/kvm/paging_tmpl.h
> @@ -360,7 +360,7 @@ retry_walk:
>  			goto error;
>  
>  		if (unlikely(is_rsvd_bits_set(mmu, pte, walker->level))) {
> -			errcode |= PFERR_RSVD_MASK | PFERR_PRESENT_MASK;
> +			errcode = PFERR_RSVD_MASK | PFERR_PRESENT_MASK;
>  			goto error;
>  		}
>