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

[Joerg Roedel <joerg.roedel@amd.com>]

On Wed, Apr 30, 2008 at 10:45:12AM +0200, Jan Kiszka wrote:
> 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)

Ah, indeed. Thanks.

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