Hi Colton, On Mon, Jan 29, 2024 at 09:39:17PM +0000, Colton Lewis wrote: > Add KVM_CAP_ARM_WFX_PASSTHROUGH capability to always allow WFE/WFI > instructions to run without trapping. Current behavior is to only > allow this if the vcpu is the only task running. This commit keeps the > old behavior when the capability is not set. > > This allows userspace to set deterministic behavior and increase > efficiency for platforms with direct interrupt injection support. Marc and I actually had an offlist conversation (shame on us!) about this very topic since there are users asking for the _opposite_ of this patch (unconditionally trap) [*]. I had originally wanted something like this, but Marc made the very good point that (1) the behavior of WFx traps is in no way user-visible and (2) it is entirely an IMP DEF behavior. The architecture only requires the traps be effective if the instruction does not complete in finite time. We need to think of an interface that doesn't depend on implementation-specific behavior, such as a control based on runqueue depth. [*] https://lore.kernel.org/kvmarm/a481ef04-ddd2-dfc1-41b1-d2ec45c6a3b5@xxxxxxxxxx/ -- Thanks, Oliver
