Re: [Xen-devel] [PATCH 07/10] x86/spec_ctrl: Explicitly set Xen's default MSR_SPEC_CTRL value

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, May 11, 2018 at 11:38:11AM +0100, Andrew Cooper wrote:
> @@ -417,6 +419,32 @@ void __init init_speculation_mitigations(void)
>          setup_clear_cpu_cap(X86_FEATURE_NO_XPTI);
>  
>      print_details(thunk, caps);
> +
> +    /*
> +     * If MSR_SPEC_CTRL is available, apply Xen's default setting and discard
> +     * any firmware settings.  For performance reasons on native hardware, we
> +     * delay applying non-zero settings until after dom0 has been 
> constructed.
> +     */
> +    if ( boot_cpu_has(X86_FEATURE_IBRSB) )
> +    {
> +        bsp_delay_spec_ctrl = !cpu_has_hypervisor && default_xen_spec_ctrl;
> +

Why is cpu_has_hypervisor needed here?  This should help nested case as
well. And it wouldn't make the setup less secure, right?

Wei.

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