Re: Implement generic double fault generation mechanism

[Gleb Natapov <gleb@redhat.com>]

On Fri, May 08, 2009 at 04:27:28PM +0800, Dong, Eddie wrote:
> Gleb Natapov wrote:
> >> +
> >> +static int exception_class(int vector)
> >> +{
> >> +	if (vector == 14)
> >> +		return EXCPT_PF;
> >> +	else if (vector == 0 || (vector >= 10 && vector <= 13)) +		return
> >> EXCPT_CONTRIBUTORY; +	else
> >> +		return EXCPT_BENIGN;
> >> +}
> >> +
> > This makes double fault (8) benign exception. Surely not what you
> > want. 
> 
> double fault fall into neither of above class per SDM. But it should be 
> checked earlier than generating DB fault. See new updated.
> >> +	/* to check exception */
> >> +	prev_nr = vcpu->arch.exception.nr;
> >> +	class2 = exception_class(nr);
> >> +	class1 = exception_class(prev_nr);
> >> +	if ((class1 == EXCPT_CONTRIBUTORY && class2 == EXCPT_CONTRIBUTORY)
> >> +		|| (class1 == EXCPT_PF && class2 != EXCPT_BENIGN)) {
> >> +		/* generate double fault per SDM Table 5-5 */
> >> +		printk(KERN_DEBUG "kvm: double fault 0x%x on 0x%x\n",
> >> +			prev_nr, nr); +		vcpu->arch.exception.pending = true;
> >> +		vcpu->arch.exception.has_error_code = 1;
> >> +		vcpu->arch.exception.nr = DF_VECTOR;
> >> +		vcpu->arch.exception.error_code = 0;
> >> +		if (prev_nr == DF_VECTOR) {
> >> +			/* triple fault -> shutdown */
> >> +			set_bit(KVM_REQ_TRIPLE_FAULT, &vcpu->requests); +		}
> >> +	} else
> >> +		printk(KERN_ERR "Exception 0x%x on 0x%x happens serially\n",
> >> +			prev_nr, nr); +}
> > When two exceptions happens serially is is better to replace pending
> > exception with a new one. This way the first exception (that is lost)
> > will be regenerated when instruction will be re-executed.
> 
> Do you want it to be covered for now? For exception, it is easy but for IRQ, it needs to be pushed back.
> 
Yes I want it to be covered now otherwise any serial exception generates
flood of "Exception happens serially" messages. This function does not
handle IRQ so no problem there.


> Thx, eddie
> 
> 
> 
>     Move Double-Fault generation logic out of page fault
>     exception generating function to cover more generic case.
>     
>     Signed-off-by: Eddie Dong <eddie.dong@intel.com>
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index ab1fdac..d0e75a2 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -162,12 +162,60 @@ void kvm_set_apic_base(struct kvm_vcpu *vcpu, u64 data)
>  }
>  EXPORT_SYMBOL_GPL(kvm_set_apic_base);
>  
> +#define EXCPT_BENIGN		0
> +#define EXCPT_CONTRIBUTORY	1
> +#define EXCPT_PF		2
> +
> +static int exception_class(int vector)
> +{
> +	if (vector == 14)
> +		return EXCPT_PF;
> +	else if (vector == 0 || (vector >= 10 && vector <= 13))
> +		return EXCPT_CONTRIBUTORY;
> +	else
> +		return EXCPT_BENIGN;
> +}
> +
> +static void kvm_multiple_exception(struct kvm_vcpu *vcpu,
> +		unsigned nr, bool has_error, u32 error_code)
> +{
> +	u32 prev_nr;
> +	int class1, class2;
> +
> +	if (!vcpu->arch.exception.pending) {
> +		vcpu->arch.exception.pending = true;
> +		vcpu->arch.exception.has_error_code = has_error;
> +		vcpu->arch.exception.nr = nr;
> +		vcpu->arch.exception.error_code = error_code;
> +		return;
> +	}
> +
> +	/* to check exception */
> +	prev_nr = vcpu->arch.exception.nr;
> +	if (prev_nr == DF_VECTOR) {
> +		/* triple fault -> shutdown */
> +		set_bit(KVM_REQ_TRIPLE_FAULT, &vcpu->requests);
> +		return;
> +	}
> +	class1 = exception_class(prev_nr);
> +	class2 = exception_class(nr);
> +	if ((class1 == EXCPT_CONTRIBUTORY && class2 == EXCPT_CONTRIBUTORY)
> +		|| (class1 == EXCPT_PF && class2 != EXCPT_BENIGN)) {
> +		/* generate double fault per SDM Table 5-5 */
> +		printk(KERN_DEBUG "kvm: double fault 0x%x on 0x%x\n",
> +			prev_nr, nr);
> +		vcpu->arch.exception.pending = true;
> +		vcpu->arch.exception.has_error_code = true;
> +		vcpu->arch.exception.nr = DF_VECTOR;
> +		vcpu->arch.exception.error_code = 0;
> +	} else
> +		printk(KERN_ERR "Exception 0x%x on 0x%x happens serially\n",
> +			prev_nr, nr);
> +}
> +
>  void kvm_queue_exception(struct kvm_vcpu *vcpu, unsigned nr)
>  {
> -	WARN_ON(vcpu->arch.exception.pending);
> -	vcpu->arch.exception.pending = true;
> -	vcpu->arch.exception.has_error_code = false;
> -	vcpu->arch.exception.nr = nr;
> +	kvm_multiple_exception(vcpu, nr, false, 0);
>  }
>  EXPORT_SYMBOL_GPL(kvm_queue_exception);
>  
> @@ -176,18 +224,6 @@ void kvm_inject_page_fault(struct kvm_vcpu *vcpu, unsigned long addr,
>  {
>  	++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);
>  }
> @@ -200,11 +236,7 @@ EXPORT_SYMBOL_GPL(kvm_inject_nmi);
>  
>  void kvm_queue_exception_e(struct kvm_vcpu *vcpu, unsigned nr, u32 error_code)
>  {
> -	WARN_ON(vcpu->arch.exception.pending);
> -	vcpu->arch.exception.pending = true;
> -	vcpu->arch.exception.has_error_code = true;
> -	vcpu->arch.exception.nr = nr;
> -	vcpu->arch.exception.error_code = error_code;
> +	kvm_multiple_exception(vcpu, nr, true, error_code);
>  }
>  EXPORT_SYMBOL_GPL(kvm_queue_exception_e);
>  


--
			Gleb.