Re: [PATCH 02/10] KVM: nVMX: Detect shadow-vmcs capability

[Gleb Natapov <gleb@redhat.com>]

On Wed, Apr 17, 2013 at 02:51:40PM +0300, Abel Gordon wrote:
> Add logic required to detect if shadow-vmcs is supported by the
> processor. Introduce a new kernel module parameter to specify if L0 should use
> shadow vmcs (or not) to run L1.
> 
> Signed-off-by: Abel Gordon <abelg@il.ibm.com>
> ---
>  arch/x86/kvm/vmx.c |   25 ++++++++++++++++++++++++-
>  1 file changed, 24 insertions(+), 1 deletion(-)
> 
> --- .before/arch/x86/kvm/vmx.c	2013-04-17 14:20:49.000000000 +0300
> +++ .after/arch/x86/kvm/vmx.c	2013-04-17 14:20:50.000000000 +0300
> @@ -87,6 +87,8 @@ module_param(fasteoi, bool, S_IRUGO);
>  static bool __read_mostly enable_apicv = 1;
>  module_param(enable_apicv, bool, S_IRUGO);
>  
> +static bool __read_mostly enable_shadow_vmcs = 1;
> +module_param_named(enable_shadow_vmcs, enable_shadow_vmcs, bool, S_IRUGO);
>  /*
>   * If nested=1, nested virtualization is supported, i.e., guests may use
>   * VMX and be a hypervisor for its own guests. If nested=0, guests may not
> @@ -940,6 +942,18 @@ static inline bool cpu_has_vmx_wbinvd_ex
>  		SECONDARY_EXEC_WBINVD_EXITING;
>  }
>  
> +static inline bool cpu_has_vmx_shadow_vmcs(void)
> +{
> +	u64 vmx_msr;
> +	rdmsrl(MSR_IA32_VMX_MISC, vmx_msr);
> +	/* check if the cpu supports writing r/o exit information fields */
> +	if (!(vmx_msr & (1u << 29)))
I think you were going to use MSR_IA32_VMX_MISC_VMWRITE_SHADOW_RO_FIELDS
here.

> +		return false;
> +
> +	return vmcs_config.cpu_based_2nd_exec_ctrl &
> +		SECONDARY_EXEC_SHADOW_VMCS;
> +}
> +
>  static inline bool report_flexpriority(void)
>  {
>  	return flexpriority_enabled;
> @@ -2632,7 +2646,8 @@ static __init int setup_vmcs_config(stru
>  			SECONDARY_EXEC_RDTSCP |
>  			SECONDARY_EXEC_ENABLE_INVPCID |
>  			SECONDARY_EXEC_APIC_REGISTER_VIRT |
> -			SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY;
> +			SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY |
> +			SECONDARY_EXEC_SHADOW_VMCS;
>  		if (adjust_vmx_controls(min2, opt2,
>  					MSR_IA32_VMX_PROCBASED_CTLS2,
>  					&_cpu_based_2nd_exec_control) < 0)
> @@ -2833,6 +2848,8 @@ static __init int hardware_setup(void)
>  
>  	if (!cpu_has_vmx_vpid())
>  		enable_vpid = 0;
> +	if (!cpu_has_vmx_shadow_vmcs())
> +		enable_shadow_vmcs = 0;
>  
>  	if (!cpu_has_vmx_ept() ||
>  	    !cpu_has_vmx_ept_4levels()) {
> @@ -4075,6 +4092,12 @@ static u32 vmx_secondary_exec_control(st
>  		exec_control &= ~(SECONDARY_EXEC_APIC_REGISTER_VIRT |
>  				  SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY);
>  	exec_control &= ~SECONDARY_EXEC_VIRTUALIZE_X2APIC_MODE;
> +	/* SECONDARY_EXEC_SHADOW_VMCS is enabled when L1 executes VMPTRLD
> +	   (handle_vmptrld).
> +	   We can NOT enable shadow_vmcs here because we don't have yet
> +	   a current VMCS12
> +	*/
> +	exec_control &= ~SECONDARY_EXEC_SHADOW_VMCS;
>  	return exec_control;
>  }
>  
> 
> --
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--
			Gleb.