KVM: x86: improve reexecute_instruction

The current reexecute_instruction can not well detect the failed instruction
emulation. It allows guest to retry all the instructions except it accesses
on error pfn

For example, some cases are nested-write-protect - if the page we want to
write is used as PDE but it chains to itself. Under this case, we should
stop the emulation and report the case to userspace

Reviewed-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -497,6 +497,13 @@ struct kvm_vcpu_arch {
 		u64 msr_val;
 		struct gfn_to_hva_cache data;
 	} pv_eoi;
+
+	/*
+	 * Indicate whether the access faults on its page table in guest
+	 * which is set when fix page fault and used to detect unhandeable
+	 * instruction.
+	 */
+	bool write_fault_to_shadow_pgtable;
 };
 
 struct kvm_lpage_info {