KVM: arm64: Refactor user_mem_abort()

KVM: arm64: Refactor user_mem_abort()

Refactor user_mem_abort() to improve code clarity and simplify
assumptions within the function.

Key changes include:

* Immediately set force_pte to true at the beginning of the function if
  logging_active is true. This simplifies the flow and makes the
  condition for forcing a PTE more explicit.

* Remove the misleading comment stating that logging_active is
  guaranteed to never be true for VM_PFNMAP memslots, as this assertion
  is not entirely correct.

* Extract reusable code blocks into new helper functions:
  * prepare_mmu_memcache(): Encapsulates the logic for preparing and
    topping up the MMU page cache.
  * adjust_nested_fault_perms(): Isolates the adjustments to shadow S2
    permissions and the encoding of nested translation levels.

* Update min(a, (long)b) to min_t(long, a, b) for better type safety and
  consistency.

* Perform other minor tidying up of the code.

These changes primarily aim to simplify user_mem_abort() and make its
logic easier to understand and maintain, setting the stage for future
modifications.

Reviewed-by: Gavin Shan <gshan@redhat.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Tao Chan <chentao@kylinos.cn>
Signed-off-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20250729225455.670324-18-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>