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

Vitaly Kuznetsov
2020-09-24T12:34:25Z

Sean Christopherson <sean.j.christopherson@intel.com> writes:

> 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);
> +

Here, were you intended to replace WARN_ON_ONCE() with KVM_BUG_ON() or
this is just a stray newline added?

> 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)) {

Do we want to allow userspace to continue executing the guest or should
we make KVM_REQ_VM_BUGGED permanent by replacing kvm_check_request()
with kvm_test_request()?

> + 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;

--
Vitaly