UPSTREAM: KVM: arm64: Detect and handle hypervisor stack overflows

The hypervisor stacks (for both nVHE Hyp mode and nVHE protected mode)
are aligned such  that any valid stack address has PAGE_SHIFT bit as 1.
This allows us to conveniently check for overflow in the exception entry
without corrupting any GPRs. We won't recover from a stack overflow so
panic the hypervisor.

Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220420214317.3303360-6-kaleshsingh@google.com


(cherry picked from commit 66de19fa)
Signed-off-by: Will Deacon <willdeacon@google.com>
Bug: 233587962
Bug: 233588291
Change-Id: Ic0f68bc0fac9e14818907347569e4b821fa1c117