linux-kernel - Re: [PATCH 2/6] KVM: VMX: remove bogus check for invalid EPT violation

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Message-ID: <1e1fbaf4-8ef3-a049-0611-fe810ee1c501@redhat.com>
Date:   Mon, 3 Apr 2017 13:17:02 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH 2/6] KVM: VMX: remove bogus check for invalid EPT
 violation

On 30.03.2017 11:55, Paolo Bonzini wrote:
> handle_ept_violation is checking for "guest-linear-address invalid" +
> "not a paging-structure walk".  However, _all_ EPT violations without
> a valid guest linear address are paging structure walks, because those
> EPT violations happen when loading the guest PDPTEs.
> 
> Therefore, the check can never be true, and even if it were, KVM doesn't
> care about the guest linear address; it only uses the guest *physical*
> address VMCS field.  So, remove the check altogether.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/vmx.c | 14 --------------
>  1 file changed, 14 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 0e61b9226bf2..1c372600a962 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -6208,23 +6208,9 @@ static int handle_ept_violation(struct kvm_vcpu *vcpu)
>  	unsigned long exit_qualification;
>  	gpa_t gpa;
>  	u32 error_code;
> -	int gla_validity;
>  
>  	exit_qualification = vmcs_readl(EXIT_QUALIFICATION);
>  
> -	gla_validity = (exit_qualification >> 7) & 0x3;
> -	if (gla_validity == 0x2) {
> -		printk(KERN_ERR "EPT: Handling EPT violation failed!\n");
> -		printk(KERN_ERR "EPT: GPA: 0x%lx, GVA: 0x%lx\n",
> -			(long unsigned int)vmcs_read64(GUEST_PHYSICAL_ADDRESS),
> -			vmcs_readl(GUEST_LINEAR_ADDRESS));
> -		printk(KERN_ERR "EPT: Exit qualification is 0x%lx\n",
> -			(long unsigned int)exit_qualification);
> -		vcpu->run->exit_reason = KVM_EXIT_UNKNOWN;
> -		vcpu->run->hw.hardware_exit_reason = EXIT_REASON_EPT_VIOLATION;
> -		return 0;
> -	}
> -
>  	/*
>  	 * EPT violation happened while executing iret from NMI,
>  	 * "blocked by NMI" bit has to be set before next VM entry.
> 

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 

Thanks,

David