Re: [patch 0/2] Handle multiple exceptions (fixes Win2003 reboot by triple fault)

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

Gleb Natapov wrote:
> On Wed, Nov 11, 2009 at 05:29:47PM -0200, Marcelo Tosatti wrote:
>> I suppose a complete fix would be to follow the "Conditions for
>> Generating a Double Fault" with support for handling exceptions
>> serially.
>>
>> But this works for me.
>>
> I prefer proper solution. Like one attached (this is combination of ths
> patch by Eddie Dong and my fix):

Nice, preferred here as well. I only have a minor comment below.

> 
> 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>
> Signed-off-by: Gleb Natapov <gleb@redhat.com>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 76c8375..88c4490 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -248,12 +248,61 @@ 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))

xx_VECTOR?

> +		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) {
> +	queue:
> +		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 */
> +		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
> +		/* replace previous exception with a new one in a hope
> +		   that instruction re-execution will regenerate lost
> +		   exception */
> +		goto queue;
> +}
> +
>  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);
>  
> @@ -261,25 +310,6 @@ void kvm_inject_page_fault(struct kvm_vcpu *vcpu, unsigned long addr,
>  			   u32 error_code)
>  {
>  	++vcpu->stat.pf_guest;
> -
> -	if (vcpu->arch.exception.pending) {
> -		switch(vcpu->arch.exception.nr) {
> -		case DF_VECTOR:
> -			/* triple fault -> shutdown */
> -			set_bit(KVM_REQ_TRIPLE_FAULT, &vcpu->requests);
> -			return;
> -		case PF_VECTOR:
> -			vcpu->arch.exception.nr = DF_VECTOR;
> -			vcpu->arch.exception.error_code = 0;
> -			return;
> -		default:
> -			/* replace previous exception with a new one in a hope
> -			   that instruction re-execution will regenerate lost
> -			   exception */
> -			vcpu->arch.exception.pending = false;
> -			break;
> -		}
> -	}
>  	vcpu->arch.cr2 = addr;
>  	kvm_queue_exception_e(vcpu, PF_VECTOR, error_code);
>  }
> @@ -292,11 +322,7 @@ 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);
>  

Jan