Re: [PATCH RESEND v10 1/2] xen+tools: Report Interrupt Controller Virtualization capabilities on x86

[Jan Beulich <jbeulich@xxxxxxxx>]

On 29.06.2022 15:55, Jane Malalane wrote:
> Add XEN_SYSCTL_PHYSCAP_X86_ASSISTED_XAPIC and
> XEN_SYSCTL_PHYSCAP_X86_ASSISTED_X2APIC to report accelerated xAPIC and
> x2APIC, on x86 hardware. This is so that xAPIC and x2APIC virtualization
> can subsequently be enabled on a per-domain basis.
> No such features are currently implemented on AMD hardware.
> 
> HW assisted xAPIC virtualization will be reported if HW, at the
> minimum, supports virtualize_apic_accesses as this feature alone means
> that an access to the APIC page will cause an APIC-access VM exit. An
> APIC-access VM exit provides a VMM with information about the access
> causing the VM exit, unlike a regular EPT fault, thus simplifying some
> internal handling.
> 
> HW assisted x2APIC virtualization will be reported if HW supports
> virtualize_x2apic_mode and, at least, either apic_reg_virt or
> virtual_intr_delivery. This also means that
> sysctl follows the conditionals in vmx_vlapic_msr_changed().
> 
> For that purpose, also add an arch-specific "capabilities" parameter
> to struct xen_sysctl_physinfo.
> 
> Note that this interface is intended to be compatible with AMD so that
> AVIC support can be introduced in a future patch. Unlike Intel that
> has multiple controls for APIC Virtualization, AMD has one global
> 'AVIC Enable' control bit, so fine-graining of APIC virtualization
> control cannot be done on a common interface.
> 
> Suggested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Signed-off-by: Jane Malalane <jane.malalane@xxxxxxxxxx>
> Reviewed-by: "Roger Pau Monné" <roger.pau@xxxxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> Reviewed-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>

Could you please clarify whether you did drop Kevin's R-b (which, a
little unhelpfully, he provided in reply to v9 a week after you had
posted v10) because of ...

> v10:
>  * Make assisted_x{2}apic_available conditional upon _vmx_cpu_up()

... this, requiring him to re-offer the tag? Until told otherwise I
will assume so.

Jan