KVM: x86: Return emulator error if RDMSR/WRMSR emulation failed

The return value of emulator_{get|set}_mst_with_filter() is confused,
since msr access error and emulator error are mixed. Although,
KVM_MSR_RET_* doesn't conflict with X86EMUL_IO_NEEDED at present, it is
better to convert msr access error to emulator error if error value is
needed.

So move "r < 0" handling for wrmsr emulation into the set helper function,
then only X86EMUL_* is returned in the helper functions. Also add "r < 0"
check in the get helper function, although KVM doesn't return -errno
today, but assuming that will always hold true is unnecessarily risking.
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
Link: https://lore.kernel.org/r/09b2847fc3bcb8937fb11738f0ccf7be7f61d9dd.1661930557.git.houwenlong.hwl@antgroup.com
[sean: wrap changelog less aggressively]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/emulate.c

@@ -3647,13 +3647,10 @@ static int em_wrmsr(struct x86_emulate_ctxt *ctxt)
 		| ((u64)reg_read(ctxt, VCPU_REGS_RDX) << 32);
 	r = ctxt->ops->set_msr_with_filter(ctxt, msr_index, msr_data);
 
-	if (r == X86EMUL_IO_NEEDED)
-		return r;
-
-	if (r > 0)
+	if (r == X86EMUL_PROPAGATE_FAULT)
 		return emulate_gp(ctxt, 0);
 
-	return r < 0 ? X86EMUL_UNHANDLEABLE : X86EMUL_CONTINUE;
+	return r;
 }
 
 static int em_rdmsr(struct x86_emulate_ctxt *ctxt)
@@ -3664,15 +3661,14 @@ static int em_rdmsr(struct x86_emulate_ctxt *ctxt)
 
 	r = ctxt->ops->get_msr_with_filter(ctxt, msr_index, &msr_data);
 
-	if (r == X86EMUL_IO_NEEDED)
-		return r;
-
-	if (r)
+	if (r == X86EMUL_PROPAGATE_FAULT)
 		return emulate_gp(ctxt, 0);
 
-	*reg_write(ctxt, VCPU_REGS_RAX) = (u32)msr_data;
-	*reg_write(ctxt, VCPU_REGS_RDX) = msr_data >> 32;
-	return X86EMUL_CONTINUE;
+	if (r == X86EMUL_CONTINUE) {
+		*reg_write(ctxt, VCPU_REGS_RAX) = (u32)msr_data;
+		*reg_write(ctxt, VCPU_REGS_RDX) = msr_data >> 32;
+	}
+	return r;
 }
 
 static int em_store_sreg(struct x86_emulate_ctxt *ctxt, int segment)

arch/x86/kvm/x86.c

@@ -7920,14 +7920,17 @@ static int emulator_get_msr_with_filter(struct x86_emulate_ctxt *ctxt,
 	int r;
 
 	r = kvm_get_msr_with_filter(vcpu, msr_index, pdata);
+	if (r < 0)
+		return X86EMUL_UNHANDLEABLE;
 
-	if (r && kvm_msr_user_space(vcpu, msr_index, KVM_EXIT_X86_RDMSR, 0,
-				    complete_emulated_rdmsr, r)) {
-		/* Bounce to user space */
-		return X86EMUL_IO_NEEDED;
+	if (r) {
+		if (kvm_msr_user_space(vcpu, msr_index, KVM_EXIT_X86_RDMSR, 0,
+				       complete_emulated_rdmsr, r))
+			return X86EMUL_IO_NEEDED;
+		return X86EMUL_PROPAGATE_FAULT;
 	}
 
-	return r;
+	return X86EMUL_CONTINUE;
 }
 
 static int emulator_set_msr_with_filter(struct x86_emulate_ctxt *ctxt,
@@ -7937,14 +7940,17 @@ static int emulator_set_msr_with_filter(struct x86_emulate_ctxt *ctxt,
 	int r;
 
 	r = kvm_set_msr_with_filter(vcpu, msr_index, data);
+	if (r < 0)
+		return X86EMUL_UNHANDLEABLE;
 
-	if (r && kvm_msr_user_space(vcpu, msr_index, KVM_EXIT_X86_WRMSR, data,
-				    complete_emulated_msr_access, r)) {
-		/* Bounce to user space */
-		return X86EMUL_IO_NEEDED;
+	if (r) {
+		if (kvm_msr_user_space(vcpu, msr_index, KVM_EXIT_X86_WRMSR, data,
+				       complete_emulated_msr_access, r))
+			return X86EMUL_IO_NEEDED;
+		return X86EMUL_PROPAGATE_FAULT;
 	}
 
-	return r;
+	return X86EMUL_CONTINUE;
 }
 
 static int emulator_get_msr(struct x86_emulate_ctxt *ctxt,