Re: [RFC][PATCH] Add support for the GUEST_SMBASE VMCS field for Intel VT-x.

[Avi Kivity <avi@redhat.com>]

On 05/18/2012 12:34 PM, Matthias Lange wrote:
> Hi,
>
> I was playing around with kvm's nested virtualization feature on Intel
> VT-x. When trying to access the GUEST_SMBASE (offset 0x4828)field of the
> VMCS I got a "VMREAD/VMWRITE from/to unsupported VMCS component" error.
> According to the Intel manual this field is not optional. The error
> results from the "vmcs_field_to_offset" function in vmx.c because the
> offset of GUEST_SMBASE is not defined.
>
> The following patch adds support for the GUEST_SMBASE field. This allows
> hypervisors running inside kvm read/write access to this field. I have
> tested this to work on a Core i5 machine.
>
> diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
> index 31f180c..6a14720 100644
> --- a/arch/x86/include/asm/vmx.h
> +++ b/arch/x86/include/asm/vmx.h
> @@ -194,6 +194,7 @@ enum vmcs_field {
>  	GUEST_TR_AR_BYTES               = 0x00004822,
>  	GUEST_INTERRUPTIBILITY_INFO     = 0x00004824,
>  	GUEST_ACTIVITY_STATE            = 0X00004826,
> +	GUEST_SMBASE			= 0x00004828,
>  	GUEST_SYSENTER_CS               = 0x0000482A,
>  	HOST_IA32_SYSENTER_CS           = 0x00004c00,
>  	CR0_GUEST_HOST_MASK             = 0x00006000,
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 4ff0ab9..0063743 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -285,6 +285,7 @@ struct __packed vmcs12 {
>  	u32 guest_tr_ar_bytes;
>  	u32 guest_interruptibility_info;
>  	u32 guest_activity_state;
> +	u32 guest_smbase;
>  	u32 guest_sysenter_cs;
>  	u32 host_ia32_sysenter_cs;
>  	u32 padding32[8]; /* room for future expansion */
> @@ -546,6 +547,7 @@ static unsigned short vmcs_field_to_offset_table[] = {
>

vmcs12 is an ABI, so you can't insert fields at random.  Grab one from
padding32.

-- 
error compiling committee.c: too many arguments to function