Use kvm_mmu_unprotect_gfn_and_retry() in reexecute_instruction() to pick
up protection against infinite loops, e.g. if KVM somehow manages to
encounter an unsupported instruction and unprotecting the gfn doesn't
allow the vCPU to make forward progress.  Other than that, the retry-on-
failure logic is a functionally equivalent, open coded version of
kvm_mmu_unprotect_gfn_and_retry().

Note, the emulation failure path still isn't fully protected, as KVM
won't update the retry protection fields if no shadow pages are zapped
(but this change is still a step forward).  That flaw will be addressed
in a future patch.
Reviewed-by: Yuan Yao <yuan.yao@intel.com>
Link: https://lore.kernel.org/r/20240831001538.336683-18-seanjc@google.comSigned-off-by: Sean Christopherson <seanjc@google.com>