linux-kernel - Re: [PATCH] x86: correctly initialize the CS base on reset

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Message-ID: <20130319154319.GF19292@redhat.com>
Date:	Tue, 19 Mar 2013 17:43:19 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH] x86: correctly initialize the CS base on reset

On Tue, Mar 19, 2013 at 04:30:26PM +0100, Paolo Bonzini wrote:
> The CS base was initialized to 0 on VMX (wrong, but usually overridden
> by userspace before starting) or 0xf0000 on SVM.  The correct value is
> 0xffff0000, and VMX is able to emulate it now, so use it.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Reviewed-by: Gleb Natapov <gleb@...hat.com>

> ---
>  arch/x86/kvm/svm.c | 8 +-------
>  arch/x86/kvm/vmx.c | 1 +
>  2 files changed, 2 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 7219a40..7a46c1f 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -1131,17 +1131,11 @@ static void init_vmcb(struct vcpu_svm *svm)
>  	init_seg(&save->gs);
>  
>  	save->cs.selector = 0xf000;
> +	save->cs.base = 0xffff0000;
>  	/* Executable/Readable Code Segment */
>  	save->cs.attrib = SVM_SELECTOR_READ_MASK | SVM_SELECTOR_P_MASK |
>  		SVM_SELECTOR_S_MASK | SVM_SELECTOR_CODE_MASK;
>  	save->cs.limit = 0xffff;
> -	/*
> -	 * cs.base should really be 0xffff0000, but vmx can't handle that, so
> -	 * be consistent with it.
> -	 *
> -	 * Replace when we have real mode working for vmx.
> -	 */
> -	save->cs.base = 0xf0000;
>  
>  	save->gdtr.limit = 0xffff;
>  	save->idtr.limit = 0xffff;
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 4a0bafe..c75c25d 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -4133,6 +4133,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu)
>  
>  	seg_setup(VCPU_SREG_CS);
>  	vmcs_write16(GUEST_CS_SELECTOR, 0xf000);
> +	vmcs_write32(GUEST_CS_BASE, 0xffff0000);
>  
>  	seg_setup(VCPU_SREG_DS);
>  	seg_setup(VCPU_SREG_ES);
> -- 
> 1.8.1.4
> 
> --
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--
			Gleb.
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