Re: [PATCH] x86: handle double and triple faults for every exception

[Jan Kiszka <jan.kiszka@siemens.com>]

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 <joerg.roedel@amd.com>
> Cc: Jan Kiszka <jan.kiszka@siemens.com>
> ---
>  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 <jan.kiszka@siemens.com>

---
 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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