Re: [PATCH v2 1/2] xen+tools: Report Interrupt Controller Virtualization capabilities on x86

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Feb 07, 2022 at 06:21:00PM +0000, Jane Malalane wrote:
> diff --git a/xen/arch/x86/hvm/vmx/vmcs.c b/xen/arch/x86/hvm/vmx/vmcs.c
> index 7ab15e07a0..4060aef1bd 100644
> --- a/xen/arch/x86/hvm/vmx/vmcs.c
> +++ b/xen/arch/x86/hvm/vmx/vmcs.c
> @@ -343,6 +343,15 @@ static int vmx_init_vmcs_config(bool bsp)
>              MSR_IA32_VMX_PROCBASED_CTLS2, &mismatch);
>      }
>  
> +    /* Check whether hardware supports accelerated xapic and x2apic. */
> +    if ( bsp )
> +    {
> +        assisted_xapic_available = cpu_has_vmx_virtualize_apic_accesses;
> +        assisted_x2apic_available = (cpu_has_vmx_apic_reg_virt ||
> +                                     cpu_has_vmx_virtual_intr_delivery) &&
> +                                    cpu_has_vmx_virtualize_x2apic_mode;

I've been think about this, and it seems kind of asymmetric that for
xAPIC mode we report hw assisted support only with
virtualize_apic_accesses available, while for x2APIC we require
virtualize_x2apic_mode plus either apic_reg_virt or
virtual_intr_delivery.

I think we likely need to be more consistent here, and report hw
assisted x2APIC support as long as virtualize_x2apic_mode is
available.

This will likely have some effect on patch 2 also, as you will have to
adjust vmx_vlapic_msr_changed.

Thanks, Roger.