Joerg Roedel wrote:
> The current KVM x86 exception code handles double and triple faults only for
> page fault exceptions. This patch extends this detection for every exception
> that gets queued for the guest.
> 
> Signed-off-by: Joerg Roedel <[EMAIL PROTECTED]>
> Cc: Jan Kiszka <[EMAIL PROTECTED]>
> ---
>  arch/x86/kvm/x86.c |   31 +++++++++++++++++--------------
>  1 files changed, 17 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 578a0c1..c05aa32 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -144,9 +144,21 @@ void kvm_set_apic_base(struct kvm_vcpu *vcpu, u64 data)
>  }
>  EXPORT_SYMBOL_GPL(kvm_set_apic_base);
>  
> +static void handle_multiple_faults(struct kvm_vcpu *vcpu)
> +{
> +     if (vcpu->arch.exception.nr != DF_VECTOR) {
> +             vcpu->arch.exception.nr = DF_VECTOR;
> +             vcpu->arch.exception.error_code = 0;
> +     } else
> +             set_bit(KVM_REQ_TRIPLE_FAULT, &vcpu->requests);
> +}
> +
>  void kvm_queue_exception(struct kvm_vcpu *vcpu, unsigned nr)
>  {
> -     WARN_ON(vcpu->arch.exception.pending);
> +     if (vcpu->arch.exception.pending) {
> +             handle_multiple_faults(vcpu);
> +             return;
> +     }
>       vcpu->arch.exception.pending = true;
>       vcpu->arch.exception.has_error_code = false;
>       vcpu->arch.exception.nr = nr;
> @@ -157,25 +169,16 @@ void kvm_inject_page_fault(struct kvm_vcpu *vcpu, 
> unsigned long addr,
>                          u32 error_code)
>  {
>       ++vcpu->stat.pf_guest;
> -     if (vcpu->arch.exception.pending) {
> -             if (vcpu->arch.exception.nr == PF_VECTOR) {
> -                     printk(KERN_DEBUG "kvm: inject_page_fault:"
> -                                     " double fault 0x%lx\n", addr);
> -                     vcpu->arch.exception.nr = DF_VECTOR;
> -                     vcpu->arch.exception.error_code = 0;
> -             } else if (vcpu->arch.exception.nr == DF_VECTOR) {
> -                     /* triple fault -> shutdown */
> -                     set_bit(KVM_REQ_TRIPLE_FAULT, &vcpu->requests);
> -             }
> -             return;
> -     }
>       vcpu->arch.cr2 = addr;
>       kvm_queue_exception_e(vcpu, PF_VECTOR, error_code);
>  }
>  
>  void kvm_queue_exception_e(struct kvm_vcpu *vcpu, unsigned nr, u32 
> error_code)
>  {
> -     WARN_ON(vcpu->arch.exception.pending);
> +     if (vcpu->arch.exception.pending) {
> +             handle_multiple_faults(vcpu);
> +             return;
> +     }
>       vcpu->arch.exception.pending = true;
>       vcpu->arch.exception.has_error_code = true;
>       vcpu->arch.exception.nr = nr;

And here is an add-on patch to fix reset-on-triple-fault:


Clear the pending original exception when raising a triple fault. This
allows to re-use the vcpu instance, e.g. after a reset which is
typically issued as reaction on the triple fault.

Signed-off-by: Jan Kiszka <[EMAIL PROTECTED]>

---
 arch/x86/kvm/x86.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Index: b/arch/x86/kvm/x86.c
===================================================================
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -149,8 +149,10 @@ static void handle_multiple_faults(struc
        if (vcpu->arch.exception.nr != DF_VECTOR) {
                vcpu->arch.exception.nr = DF_VECTOR;
                vcpu->arch.exception.error_code = 0;
-       } else
+       } else {
                set_bit(KVM_REQ_TRIPLE_FAULT, &vcpu->requests);
+               vcpu->arch.exception.pending = false;
+       }
 }
 
 void kvm_queue_exception(struct kvm_vcpu *vcpu, unsigned nr)



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