Re: [PATCH v4] x86/hvm: Widen condition for is_hvm_pv_evtchn_domain() and report fix in CPUID

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

On Fri, Jun 10, 2022 at 12:07:04PM +0100, Jane Malalane wrote:
> Have is_hvm_pv_evtchn_domain() return true for vector callbacks for
> evtchn delivery set up on a per-vCPU basis via
> HVMOP_set_evtchn_upcall_vector.
> 
> Assume that if vCPU0 uses HVMOP_set_evtchn_upcall_vector, all
> remaining vCPUs will too and thus remove is_hvm_pv_evtchn_vcpu() and
> replace sole caller with is_hvm_pv_evtchn_domain().
> 
> is_hvm_pv_evtchn_domain() returning true is a condition for setting up
> physical IRQ to event channel mappings. Therefore, also add a CPUID
> bit so that guests know whether the check in is_hvm_pv_evtchn_domain()
> will fail when using HVMOP_set_evtchn_upcall_vector. This matters for
> guests that route PIRQs over event channels since
> is_hvm_pv_evtchn_domain() is a condition in physdev_map_pirq().
> 
> The naming of the CPUID bit is quite generic about upcall support
> being available. That's done so that the define name doesn't become
> overly long.
> 
> A guest that doesn't care about physical interrupts routed over event
> channels can just test for the availability of the hypercall directly
> (HVMOP_set_evtchn_upcall_vector) without checking the CPUID bit.
> 
> Signed-off-by: Jane Malalane <jane.malalane@xxxxxxxxxx>

Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Thanks, Roger.