Re: [PATCH] kvm: cleanup CR8 handling

[Andre Przywara <andre.przywara@amd.com>]

Avi Kivity wrote:
> On 12/08/2010 01:27 PM, Andre Przywara wrote:
>> The handling of CR8 writes in KVM is currently somewhat cumbersome.
>> This patch makes it look like the other CR register handlers
>> and fixes a possible issue in VMX, where the RIP would be incremented
>> despite an injected #GP.
>>
>>   unsigned long kvm_get_cr8(struct kvm_vcpu *vcpu)
>> @@ -4104,7 +4098,7 @@ static int emulator_set_cr(int cr, unsigned long val, struct kvm_vcpu *vcpu)
>>   		res = kvm_set_cr4(vcpu, mk_cr_64(kvm_read_cr4(vcpu), val));
>>   		break;
>>   	case 8:
>> -		res = __kvm_set_cr8(vcpu, val&  0xfUL);
>> +		res = kvm_set_cr8(vcpu, val);
>>   		break;
>>   	default:
>>   		vcpu_printf(vcpu, "%s: unexpected cr %u\n", __func__, cr);
> 
> Why drop the mask?
Because it is checked in kvm_set_cr8 itself. If it is wrong, the caller 
should get a #GP as described in the manual. By masking this out we 
would never deliver the #GP to the guest.

Regards,
Andre.

-- 
Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany
Tel: +49 351 448-3567-12