Messages in this thread | | | Date | Mon, 23 May 2022 14:46:11 +0800 | Subject | Re: [PATCH v6 2/3] KVM: selftests: Add a test to get/set triple fault event | From | Chenyi Qiang <> |
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On 5/19/2022 3:20 AM, Sean Christopherson wrote: > 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; >
Maybe, A GUEST_SYNC to main() to change the request_interrupt_window also works.
> asm volatile("sti; ud2"); >
How does the "real" triple fault occur here? Through 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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