KVM: arm64: Support TLB invalidation in guest context

Typically, TLB invalidation of guest stage-2 mappings using nVHE is
performed by a hypercall originating from the host. For the invalidation
instruction to be effective, therefore, __tlb_switch_to_{guest,host}()
swizzle the active stage-2 context around the TLBI instruction.

With guest-to-host memory sharing and unsharing hypercalls
originating from the guest under pKVM, there is need to support
both guest and host VMID invalidations issued from guest context.

Replace the __tlb_switch_to_{guest,host}() functions with a more general
{enter,exit}_vmid_context() implementation which supports being invoked
from guest context and acts as a no-op if the target context matches the
running context.

Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Fuad Tabba <tabba@google.com>
Acked-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20240423150538.2103045-10-tabba@google.com


Signed-off-by: Marc Zyngier <maz@kernel.org>