[PATCH 13/14] KVM: x86: Don't panic the kernel if completing userspace I/O / MMIO goes sideways

[Sean Christopherson <seanjc@google.com>]

Kill the VM instead of the host kernel if KVM botches I/O and/or MMIO
handling.  There is zero danger to the host or guest, i.e. panicking the
host isn't remotely justified.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/x86.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index f3e2ec7e1828..5376b370b4db 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9710,7 +9710,8 @@ static int complete_fast_pio_in(struct kvm_vcpu *vcpu)
 	unsigned long val;
 
 	/* We should only ever be called with arch.pio.count equal to 1 */
-	BUG_ON(vcpu->arch.pio.count != 1);
+	if (KVM_BUG_ON(vcpu->arch.pio.count != 1, vcpu->kvm))
+		return -EIO;
 
 	if (unlikely(!kvm_is_linear_rip(vcpu, vcpu->arch.cui_linear_rip))) {
 		vcpu->arch.pio.count = 0;
@@ -11820,7 +11821,8 @@ static inline int complete_emulated_io(struct kvm_vcpu *vcpu)
 
 static int complete_emulated_pio(struct kvm_vcpu *vcpu)
 {
-	BUG_ON(!vcpu->arch.pio.count);
+	if (KVM_BUG_ON(!vcpu->arch.pio.count, vcpu->kvm))
+		return -EIO;
 
 	return complete_emulated_io(vcpu);
 }
@@ -11849,7 +11851,8 @@ static int complete_emulated_mmio(struct kvm_vcpu *vcpu)
 	struct kvm_mmio_fragment *frag;
 	unsigned len;
 
-	BUG_ON(!vcpu->mmio_needed);
+	if (KVM_BUG_ON(!vcpu->mmio_needed, vcpu->kvm))
+		return -EIO;
 
 	/* Complete previous fragment */
 	frag = &vcpu->mmio_fragments[vcpu->mmio_cur_fragment];
@@ -14262,7 +14265,8 @@ static int complete_sev_es_emulated_mmio(struct kvm_vcpu *vcpu)
 	struct kvm_mmio_fragment *frag;
 	unsigned int len;
 
-	BUG_ON(!vcpu->mmio_needed);
+	if (KVM_BUG_ON(!vcpu->mmio_needed, vcpu->kvm))
+		return -EIO;
 
 	/* Complete previous fragment */
 	frag = &vcpu->mmio_fragments[vcpu->mmio_cur_fragment];
-- 
2.53.0.414.gf7e9f6c205-goog