[RFC PATCH 3/3] KVM: x86: Use KVM_BUG/KVM_BUG_ON to handle bugs that are fatal to the VM

Sean Christopherson
2020-09-23T22:45:41Z

Add support for KVM_REQ_VM_BUGG in x86, and replace a variety of WARNs
with KVM_BUG() and KVM_BUG_ON(). Return -EIO if a KVM_BUG is hit to
align with the common KVM behavior of rejecting iocts() with -EIO if the
VM is bugged.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
arch/x86/kvm/svm/svm.c | 2 +-
arch/x86/kvm/vmx/vmx.c | 23 ++++++++++++++---------
arch/x86/kvm/x86.c | 4 ++++
3 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 3da5b2f1b4a1..e684794c6249 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1380,7 +1380,7 @@ static void svm_cache_reg(struct kvm_vcpu *vcpu, enum kvm_reg reg)
load_pdptrs(vcpu, vcpu->arch.walk_mmu, kvm_read_cr3(vcpu));
break;
default:
- WARN_ON_ONCE(1);
+ KVM_BUG_ON(1, vcpu->kvm);
}
}

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 6f9a0c6d5dc5..810d46ab0a47 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2250,7 +2250,7 @@ static void vmx_cache_reg(struct kvm_vcpu *vcpu, enum kvm_reg reg)
vcpu->arch.cr4 |= vmcs_readl(GUEST_CR4) & guest_owned_bits;
break;
default:
- WARN_ON_ONCE(1);
+ KVM_BUG_ON(1, vcpu->kvm);
break;
}
}
@@ -4960,6 +4960,7 @@ static int handle_cr(struct kvm_vcpu *vcpu)
return kvm_complete_insn_gp(vcpu, err);
case 3:
WARN_ON_ONCE(enable_unrestricted_guest);
+
err = kvm_set_cr3(vcpu, val);
return kvm_complete_insn_gp(vcpu, err);
case 4:
@@ -4985,14 +4986,13 @@ static int handle_cr(struct kvm_vcpu *vcpu)
}
break;
case 2: /* clts */
- WARN_ONCE(1, "Guest should always own CR0.TS");
- vmx_set_cr0(vcpu, kvm_read_cr0_bits(vcpu, ~X86_CR0_TS));
- trace_kvm_cr_write(0, kvm_read_cr0(vcpu));
- return kvm_skip_emulated_instruction(vcpu);
+ KVM_BUG(1, vcpu->kvm, "Guest always owns CR0.TS");
+ return -EIO;
case 1: /*mov from cr*/
switch (cr) {
case 3:
WARN_ON_ONCE(enable_unrestricted_guest);
+
val = kvm_read_cr3(vcpu);
kvm_register_write(vcpu, reg, val);
trace_kvm_cr_read(cr, val);
@@ -5330,7 +5330,9 @@ static int handle_ept_misconfig(struct kvm_vcpu *vcpu)

static int handle_nmi_window(struct kvm_vcpu *vcpu)
{
- WARN_ON_ONCE(!enable_vnmi);
+ if (KVM_BUG_ON(!enable_vnmi, vcpu->kvm))
+ return -EIO;
+
exec_controls_clearbit(to_vmx(vcpu), CPU_BASED_NMI_WINDOW_EXITING);
++vcpu->stat.nmi_window_exits;
kvm_make_request(KVM_REQ_EVENT, vcpu);
@@ -5908,7 +5910,8 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
* below) should never happen as that means we incorrectly allowed a
* nested VM-Enter with an invalid vmcs12.
*/
- WARN_ON_ONCE(vmx->nested.nested_run_pending);
+ if (KVM_BUG_ON(vmx->nested.nested_run_pending, vcpu->kvm))
+ return -EIO;

/* If guest state is invalid, start emulating */
if (vmx->emulation_required)
@@ -6258,7 +6261,9 @@ static int vmx_sync_pir_to_irr(struct kvm_vcpu *vcpu)
int max_irr;
bool max_irr_updated;

- WARN_ON(!vcpu->arch.apicv_active);
+ if (KVM_BUG_ON(!vcpu->arch.apicv_active, vcpu->kvm))
+ return -EIO;
+
if (pi_test_on(&vmx->pi_desc)) {
pi_clear_on(&vmx->pi_desc);
/*
@@ -6345,7 +6350,7 @@ static void handle_external_interrupt_irqoff(struct kvm_vcpu *vcpu)
gate_desc *desc;
u32 intr_info = vmx_get_intr_info(vcpu);

- if (WARN_ONCE(!is_external_intr(intr_info),
+ if (KVM_BUG(!is_external_intr(intr_info), vcpu->kvm,
"KVM: unexpected VM-Exit interrupt info: 0x%x", intr_info))
return;

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 17f4995e80a7..672eb5142b34 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8363,6 +8363,10 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
bool req_immediate_exit = false;

if (kvm_request_pending(vcpu)) {
+ if (kvm_check_request(KVM_REQ_VM_BUGGED, vcpu)) {
+ r = -EIO;
+ goto out;
+ }
if (kvm_check_request(KVM_REQ_GET_VMCS12_PAGES, vcpu)) {
if (unlikely(!kvm_x86_ops.nested_ops->get_vmcs12_pages(vcpu))) {
r = 0;
--
2.28.0