[PATCH v2 26/36] KVM: arm64: Defer saving/restoring system registers to vcpu load/put on VHE

[Marc Zyngier]

On 07/12/17 17:06, Christoffer Dall wrote:
> Some system registers do not affect the host kernel's execution and can
> therefore be loaded when we are about to run a VCPU and we don't have to
> restore the host state to the hardware before the time when we are
> actually about to return to userspace or schedule out the VCPU thread.
> 
> The EL1 system registers and the userspace state registers, which only
> affect EL0 execution, do not affect the host kernel's execution.
> 
> The 32-bit system registers are not used by a VHE host kernel and
> therefore don't need to be saved/restored on every entry/exit to/from
> the guest, but can be deferred to vcpu_load and vcpu_put, respectively.

Note that they are not used by the !VHE host kernel either, and I
believe they could be deferred too, although that would imply a round
trip to HYP to save/restore them. We already have such a hook there when
configuring ICH_VMCR_EL2, so we may not need much of a new infrastructure.

What do you think?

	M.
-- 
Jazz is not dead. It just smells funny...