Re: [Qemu-devel] [PATCH v3 15/20] kvm: arm/arm64: Allow tuning the physical address size for VM

[Suzuki K Poulose]

On 02/07/18 14:13, Marc Zyngier wrote:
> On 29/06/18 12:15, Suzuki K Poulose wrote:
> > Allow specifying the physical address size for a new VM via
> > the kvm_type argument for KVM_CREATE_VM ioctl. This allows
> > us to finalise the stage2 page table format as early as possible
> > and hence perform the right checks on the memory slots without
> > complication. The size is encoded as Log2(PA_Size) in the bits[7:0]
> > of the type field and can encode more information in the future if
> > required. The IPA size is still capped at 40bits.
>
> Can't we relax this? There is no technical reason (AFAICS) not to allow
> going down to 36bit IPA if the user has requested it.

Sure, we can.

> If we run on a 36bit IPA system, the default would fail. But if the user
> specified "please give me a 36bit IPA VM", we could satisfy that
> requirement and allow them to run their stupidly small guest!

Absolutely. I will fix this in the next version.

Cheers
Suzuki