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...