[PATCH v2 1/2] KVM: x86: Return emulator error if RDMSR/WRMSR emulation failed

[Hou Wenlong]

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@xxxxxxxxxx>
Signed-off-by: Hou Wenlong <houwenlong.hwl@xxxxxxxxxxxx>
---
 arch/x86/kvm/emulate.c | 20 ++++++++------------
 arch/x86/kvm/x86.c     | 26 ++++++++++++++++----------
 2 files changed, 24 insertions(+), 22 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index f092c54d1a2f..d16f7d6a81bb 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -3645,13 +3645,10 @@ 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)
@@ -3662,15 +3659,14 @@ 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)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index d7374d768296..2596f5736743 100644
--- a/arch/x86/kvm/x86.c
+++ b/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,
-- 
2.31.1