From mboxrd@z Thu Jan  1 00:00:00 1970
From: Marcelo Tosatti <mtosatti@redhat.com>
Subject: Re: [PATCH 2/7] KVM: VMX: relax check for CS register in
 rmode_segment_valid()
Date: Fri, 21 Dec 2012 21:17:16 -0200
Message-ID: <20121221231715.GA30710@amt.cnet>
References: <1355332255-26612-1-git-send-email-gleb@redhat.com>
 <1355332255-26612-3-git-send-email-gleb@redhat.com>
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Cc: kvm@vger.kernel.org
To: Gleb Natapov <gleb@redhat.com>
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On Wed, Dec 12, 2012 at 07:10:50PM +0200, Gleb Natapov wrote:
> rmode_segment_valid() checks if segment descriptor can be used to enter
> vm86 mode. VMX spec mandates that in vm86 mode CS register will be of
> type data, not code. Lets allow guest entry with vm86 mode if the only
> problem with CS register is incorrect type. Otherwise entire real mode
> will be emulated.
> 
> Signed-off-by: Gleb Natapov <gleb@redhat.com>
> ---
>  arch/x86/kvm/vmx.c |    2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 4df3991..acbe86f 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -3383,6 +3383,8 @@ static bool rmode_segment_valid(struct kvm_vcpu *vcpu, int seg)
>  	var.dpl = 0x3;
>  	var.g = 0;
>  	var.db = 0;
> +	if (seg == VCPU_SREG_CS)
> +		var.type = 0x3;
>  	ar = vmx_segment_access_rights(&var);
>  
>  	if (var.base != (var.selector << 4))
> -- 
> 1.7.10.4

But with emulate_invalid_guest_state=1, segments are not fixed on 
transition to real mode. So this patch can result in 
invalid guest state entry failure.

Does this defeat the purpose of emulate_invalid_guest_state=1?