KVM: x86 emulator: introduce read cache

Introduce read cache which is needed for instruction that require more
then one exit to userspace. After returning from userspace the instruction
will be re-executed with cached read value.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h
index 0b2729b..288cbed 100644
--- a/arch/x86/include/asm/kvm_emulate.h
+++ b/arch/x86/include/asm/kvm_emulate.h
@@ -186,6 +186,7 @@
 	unsigned long modrm_val;
 	struct fetch_cache fetch;
 	struct read_cache io_read;
+	struct read_cache mem_read;
 };
 
 struct x86_emulate_ctxt {