Re: [PATCH v4 04/11] KVM: x86/xen: Always route non-singleshot-timer vCPU hypercalls to userspace

[David Woodhouse]

On Tue, 2026-06-30 at 15:56 -0700, Sean Christopherson wrote:
> When handling Xen vCPU hypercalls, explicitly route non-singleshot-timer
> commands to userspace, *before* checking if in-kernel emulation of the Xen
> timer is enabled.  Punting hypercalls that are never accelerated by KVM
> because some other hypercall happens to be disabled is confusing and
> actively dangerous, e.g. it's easy to miss that the only reason KVM can
> bail early is because the timer-disabled case provides the same semantics
> as the implicit "default" path in the switch-statement.
> 
> Opportunistically convert the switch-statement to an if-else-statement to
> avoid having to carry code for an impossible "default" case.
> 
> For all intents and purposes, no functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>

Reviewed-by: David Woodhouse <dwmw@xxxxxxxxxxxx>

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