KVM: VMX: Inject #GP on ENCLS if vCPU has paging disabled (CR0.PG==0)

KVM: VMX: Inject #GP on ENCLS if vCPU has paging disabled (CR0.PG==0)

Inject a #GP when emulating/forwarding a valid ENCLS leaf if the vCPU has
paging disabled, e.g. if KVM is intercepting ECREATE to enforce additional
restrictions.  The pseudocode in the SDM lists all #GP triggers, including
CR0.PG=0, as being checked after the ENLCS-exiting checks, i.e. the
VM-Exit will occur before the CPU performs the CR0.PG check.

Fixes: 70210c044b4e ("KVM: VMX: Add SGX ENCLS[ECREATE] handler to enforce CPUID restrictions")
Cc: Binbin Wu <binbin.wu@linux.intel.com>
Cc: Kai Huang <kai.huang@intel.com>
Tested-by: Kai Huang <kai.huang@intel.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Link: https://lore.kernel.org/r/20230405234556.696927-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>