KVM: x86: Add an emulation type to handle completion of user exits

The next patch would use kvm_emulate_instruction() with
EMULTYPE_SKIP in complete_userspace_io callback to fix a
problem in msr access emulation. However, EMULTYPE_SKIP
only updates RIP, more things like updating interruptibility
state and injecting single-step #DBs would be done in the
callback. Since the emulator also does those things after
x86_emulate_insn(), add a new emulation type to pair with
EMULTYPE_SKIP to do those things for completion of user exits
within the emulator.
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Hou Wenlong <houwenlong93@linux.alibaba.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <8f8c8e268b65f31d55c2881a4b30670946ecfa0d.1635842679.git.houwenlong93@linux.alibaba.com>

arch/x86/include/asm/kvm_host.h

@@ -1643,7 +1643,8 @@ extern u64 kvm_mce_cap_supported;
  *
  * EMULTYPE_SKIP - Set when emulating solely to skip an instruction, i.e. to
  *		   decode the instruction length.  For use *only* by
- *		   kvm_x86_ops.skip_emulated_instruction() implementations.
+ *		   kvm_x86_ops.skip_emulated_instruction() implementations if
+ *		   EMULTYPE_COMPLETE_USER_EXIT is not set.
  *
  * EMULTYPE_ALLOW_RETRY_PF - Set when the emulator should resume the guest to
  *			     retry native execution under certain conditions,
@@ -1663,6 +1664,10 @@ extern u64 kvm_mce_cap_supported;
  *
  * EMULTYPE_PF - Set when emulating MMIO by way of an intercepted #PF, in which
  *		 case the CR2/GPA value pass on the stack is valid.
+ *
+ * EMULTYPE_COMPLETE_USER_EXIT - Set when the emulator should update interruptibility
+ *				 state and inject single-step #DBs after skipping
+ *				 an instruction (after completing userspace I/O).
  */
 #define EMULTYPE_NO_DECODE	    (1 << 0)
 #define EMULTYPE_TRAP_UD	    (1 << 1)
@@ -1671,6 +1676,7 @@ extern u64 kvm_mce_cap_supported;
 #define EMULTYPE_TRAP_UD_FORCED	    (1 << 4)
 #define EMULTYPE_VMWARE_GP	    (1 << 5)
 #define EMULTYPE_PF		    (1 << 6)
+#define EMULTYPE_COMPLETE_USER_EXIT (1 << 7)
 
 int kvm_emulate_instruction(struct kvm_vcpu *vcpu, int emulation_type);
 int kvm_emulate_instruction_from_buffer(struct kvm_vcpu *vcpu,

arch/x86/kvm/x86.c

@@ -8134,9 +8134,10 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 	}
 
 	/*
-	 * Note, EMULTYPE_SKIP is intended for use *only* by vendor callbacks
-	 * for kvm_skip_emulated_instruction().  The caller is responsible for
-	 * updating interruptibility state and injecting single-step #DBs.
+	 * EMULTYPE_SKIP without EMULTYPE_COMPLETE_USER_EXIT is intended for
+	 * use *only* by vendor callbacks for kvm_skip_emulated_instruction().
+	 * The caller is responsible for updating interruptibility state and
+	 * injecting single-step #DBs.
 	 */
 	if (emulation_type & EMULTYPE_SKIP) {
 		if (ctxt->mode != X86EMUL_MODE_PROT64)
@@ -8144,6 +8145,11 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 		else
 			ctxt->eip = ctxt->_eip;
 
+		if (emulation_type & EMULTYPE_COMPLETE_USER_EXIT) {
+			r = 1;
+			goto writeback;
+		}
+
 		kvm_rip_write(vcpu, ctxt->eip);
 		if (ctxt->eflags & X86_EFLAGS_RF)
 			kvm_set_rflags(vcpu, ctxt->eflags & ~X86_EFLAGS_RF);
@@ -8213,6 +8219,7 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 	else
 		r = 1;
 
+writeback:
 	if (writeback) {
 		unsigned long rflags = static_call(kvm_x86_get_rflags)(vcpu);
 		toggle_interruptibility(vcpu, ctxt->interruptibility);