Re: [PATCH] kvm: cleanup CR8 handling

[Avi Kivity <avi@redhat.com>]

On 12/21/2010 12:07 PM, Andre Przywara wrote:
> 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.
>

Ok.  Strictly speaking, this should be in a separate patch, since it 
fixes a bug, but this is such a minor bug it doesn't matter.  I doubt 
any guest relies on #GP on invalid CR8.

-- 
error compiling committee.c: too many arguments to function