Re: [Xen-devel] X86: generic MSRs save/restore

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 13.12.13 at 08:57, "Liu, Jinsong" <jinsong.liu@xxxxxxxxx> wrote:
> --- a/xen/arch/x86/hvm/vmx/vmx.c
> +++ b/xen/arch/x86/hvm/vmx/vmx.c
> @@ -580,6 +580,50 @@ static int vmx_load_vmcs_ctxt(struct vcp
>      return 0;
>  }
>  
> +static unsigned int __init vmx_init_msr(void)
> +{
> +    return !!cpu_has_mpx;
> +}
> +
> +static void vmx_save_msr(struct vcpu *v, struct hvm_msr *ctxt)
> +{
> +    vmx_vmcs_enter(v);
> +
> +    if ( cpu_has_mpx )
> +    {
> +        __vmread(GUEST_BNDCFGS, &ctxt->msr[ctxt->count].val);
> +        if ( ctxt->msr[ctxt->count].val )
> 
> 
> Isn't it better to remove if()?

Definitely not: That way, if the hardware support MPX but the
guest never used it, restoring the guest on an MPX-incapable
host will be possible. And when the MSR is zero, restoring on an
MPX-capable host will be correct too, as the respective VMCS
field starts out zeroed.

Jan


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