Re: Implement generic double fault generation mechanism

[Gleb Natapov <gleb@redhat.com>]

On Thu, Apr 30, 2009 at 03:24:07PM +0800, Dong, Eddie wrote:
> 
> 
>     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..51a8dad 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -162,12 +162,59 @@ 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;
> +}
> +
This makes double fault (8) benign exception. Surely not what you want.

> +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;
> +	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.

--
			Gleb.