arm64/vmm: save and restore HCRX_EL2 register

[harry.moulton_arm.com]

Summary

With the addition of the Extended Hypervisor Configuration Register
(HCRX_EL2), this change ensures that it is both set to 0 before entering
a vm, and that it is properly saved/restored.

Sponsored By: Arm Ltd
Signed-off-by: Harry Moulton <[e-mail]>

[andrew]

Does the value of the register matter when no guest is running? Does the hardware change the register when a guest is running? If not we can restrict when we save & restore it, e.g. if the host doesn't care what value it has, and it's never changed by hardware then we only need to restore it for guests and can drop the vmm_hyp_reg_store change.

[harry.moulton_arm.com]

In D48584#1108156, @andrew wrote:

Does the value of the register matter when no guest is running? Does the hardware change the register when a guest is running? If not we can restrict when we save & restore it, e.g. if the host doesn't care what value it has, and it's never changed by hardware then we only need to restore it for guests and can drop the vmm_hyp_reg_store change.

Makes sense. I think so long as HCRX_EL2 doesn't end up with some unknown value. It's being set to zero, for now, in reset_vm_el2_regs, and that's where we'll set any of it's bits in the future. So yeah, storing it in vmm_hyp_reg_store is not needed.

[andrew]

I think this is what you'll need. We need to save and restore HCRX_EL2 in the non-VHE case, and load it for a VHE guest.

sys/arm64/vmm/vmm_hyp.c

262–267

280–283

[harry.moulton_arm.com]

Addressed review comments