[PATCH v8 01/69] arm64: Add ARM64_HAS_NESTED_VIRT cpufeature

[Oliver Upton]

On Tue, Jan 31, 2023 at 09:26:56PM +0000, Marc Zyngier wrote:
> On Tue, 31 Jan 2023 20:04:15 +0000, Oliver Upton <oliver.upton at linux.dev> wrote:
> > Marc, I'm curious, how do you plan to glue hVHE + NV together (if at
> > all)? We may need two separate options for this so the user could
> > separately configure NV for their hVHE KVM instance.
> 
> I really don't plan to support them together. But if we wanted to
> support something, I'd rather express it as a composition of the
> various options, as I suggested to Suzuki earlier. Something along the
> lines of:
> 
> 	kvm-arm.mode=hvhe,nested
> 
> But the extra complexity is mind-boggling, frankly. And the result
> will suck terribly. NV is already exit-heavy, compared to single-level
> virtualisation. But now you double the cost of the exit by moving all
> the load/put work into the entry-exit phase.

Oh yeah, that wasn't a feature request, just wanted to pick your brain
for a moment :) Hopefully nobody comes along asking for it in the
future, heh.

-- 
Thanks,
Oliver