Messages in this thread Patch in this message | | | Date | Wed, 18 May 2022 19:20:32 +0000 | From | Sean Christopherson <> | Subject | Re: [PATCH v6 2/3] KVM: selftests: Add a test to get/set triple fault event |
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On Thu, Apr 21, 2022, Chenyi Qiang wrote: > +#ifndef __x86_64__ > +# error This test is 64-bit only
No need, all of KVM selftests are 64-bit only.
> +#endif > + > +#define VCPU_ID 0 > +#define ARBITRARY_IO_PORT 0x2000 > + > +/* The virtual machine object. */ > +static struct kvm_vm *vm; > + > +static void l2_guest_code(void) > +{ > + /* > + * Generate an exit to L0 userspace, i.e. main(), via I/O to an > + * arbitrary port. > + */
I think we can test a "real" triple fault without too much effort by abusing vcpu->run->request_interrupt_window. E.g. map the run struct into L2, clear PIN_BASED_EXT_INTR_MASK in vmcs12, and then in l2_guest_code() do:
asm volatile("cli");
run->request_interrupt_window = true;
asm volatile("sti; ud2");
asm volatile("inb %%dx, %%al" : : [port] "d" (ARBITRARY_IO_PORT) : "rax");
The STI shadow will block the IRQ-window VM-Exit until after the ud2, i.e. until after the triple fault is pending.
And then main() can
1. verify it got KVM_EXIT_IRQ_WINDOW_OPEN with a pending triple fault 2. clear the triple fault and re-enter L1+l2 3. continue with the existing code, e.g. verify it got KVM_EXIT_IO, stuff a pending triple fault, etc...
That said, typing that out makes me think we should technically handle/prevent this in KVM since triple fault / shutdown is kinda sorta just a special exception.
Heh, and a potentially bad/crazy idea would be to use a reserved/magic vector in kvm_vcpu_events.exception to save/restore triple fault, e.g. we could steal NMI_VECTOR.
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index f2d0ee9296b9..d58c0cfd3cd3 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -4743,7 +4743,8 @@ static int kvm_vcpu_ready_for_interrupt_injection(struct kvm_vcpu *vcpu) return (kvm_arch_interrupt_allowed(vcpu) && kvm_cpu_accept_dm_intr(vcpu) && !kvm_event_needs_reinjection(vcpu) && - !vcpu->arch.exception.pending); + !vcpu->arch.exception.pending && + !kvm_test_request(KVM_REQ_TRIPLE_FAULT, vcpu)); }
static int kvm_vcpu_ioctl_interrupt(struct kvm_vcpu *vcpu,
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