linux-kernel - Re: [PATCH] kvm: nVMX: check vmcs12 for valid activity state

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Date:	Mon, 15 Apr 2013 14:54:12 +0200
From:	Jan Kiszka <jan.kiszka@...mens.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"gnatapov@...hat.com" <gnatapov@...hat.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [PATCH] kvm: nVMX: check vmcs12 for valid activity state

On 2013-04-15 14:46, Paolo Bonzini wrote:
> KVM does not use the activity state VMCS field, and does not support
> it in nested VMX either (the corresponding bits in the misc VMX feature
> MSR are zero).  Fail entry if the activity state is set to anything but
> "active".

Ah, that indeed simplifies the issue.

> 
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/vmx.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index c75c25d..589e79a 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -7223,6 +7223,11 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)
>  		return 1;
>  	}
>  
> +	if (vmcs12->guest_activity_state != 0) {

GUEST_ACTIVITY_ACTIVE, please.

> +		nested_vmx_failValid(vcpu, VMXERR_ENTRY_INVALID_CONTROL_FIELD);
> +		return 1;
> +	}
> +
>  	if ((vmcs12->cpu_based_vm_exec_control & CPU_BASED_USE_MSR_BITMAPS) &&
>  			!IS_ALIGNED(vmcs12->msr_bitmap, PAGE_SIZE)) {
>  		/*TODO: Also verify bits beyond physical address width are 0*/
> 

That means we also do not need to read and write the corresponding VMCS
field on L1/L2 transitions - avoids any risk of setting it to an
unsupported value. So I would fold it into this change.

Jan

-- 
Siemens AG, Corporate Technology, CT RTC ITP SDP-DE
Corporate Competence Center Embedded Linux
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