Re: [PATCH 10/10] KVM: nVMX: Enable and disable shadow vmcs functionality

[Gleb Natapov <gleb@redhat.com>]

On Wed, Apr 17, 2013 at 02:55:40PM +0300, Abel Gordon wrote:
> Once L1 loads VMCS12 we enable shadow-vmcs capability and copy all the VMCS12
> shadowed fields to the shadow vmcs.  When we release the VMCS12, we also
> disable shadow-vmcs capability.
> 
> Signed-off-by: Abel Gordon <abelg@il.ibm.com>
> ---
>  arch/x86/kvm/vmx.c |   11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> --- .before/arch/x86/kvm/vmx.c	2013-04-17 14:20:51.000000000 +0300
> +++ .after/arch/x86/kvm/vmx.c	2013-04-17 14:20:51.000000000 +0300
> @@ -5590,12 +5590,17 @@ static int nested_vmx_check_permission(s
>  
>  static inline void nested_release_vmcs12(struct vcpu_vmx *vmx)
>  {
> +	u32 exec_control;
>  	if (enable_shadow_vmcs) {
>  		if (vmx->nested.current_vmcs12 != NULL) {
>  			/* copy to memory all shadowed fields in case
>  			   they were modified */
>  			copy_shadow_to_vmcs12(vmx);
>  			vmx->nested.sync_shadow_vmcs = false;
> +			exec_control = vmcs_read32(SECONDARY_VM_EXEC_CONTROL);
> +			exec_control &= ~SECONDARY_EXEC_SHADOW_VMCS;
> +			vmcs_write32(SECONDARY_VM_EXEC_CONTROL, exec_control);
> +			vmcs_write64(VMCS_LINK_POINTER, -1ull);
>  			free_vmcs(vmx->nested.current_shadow_vmcs);
>  		}
>  	}
> @@ -6084,6 +6089,7 @@ static int handle_vmptrld(struct kvm_vcp
>  	gpa_t vmptr;
>  	struct x86_exception e;
>  	struct vmcs *shadow_vmcs;
> +	u32 exec_control;
>  
>  	if (!nested_vmx_check_permission(vcpu))
>  		return 1;
> @@ -6140,6 +6146,11 @@ static int handle_vmptrld(struct kvm_vcp
>  			/* init shadow vmcs */
>  			vmcs_clear(shadow_vmcs);
>  			vmx->nested.current_shadow_vmcs = shadow_vmcs;
> +			exec_control = vmcs_read32(SECONDARY_VM_EXEC_CONTROL);
> +			exec_control |= SECONDARY_EXEC_SHADOW_VMCS;
> +			vmcs_write32(SECONDARY_VM_EXEC_CONTROL, exec_control);
> +			vmcs_write64(VMCS_LINK_POINTER,
> +				     __pa(shadow_vmcs));
How hard would it be to disable shadowing for individual vmcs if shadow
vmcs allocation fails? It bothers me a little that we can fail perfectly
valid vmptrld() because of failed allocation.


>  			vmx->nested.sync_shadow_vmcs = true;
>  		}
>  	}
> 
> --
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--
			Gleb.