[PATCH 08/26] KVM: PPC: Add PV guest critical sections

[Alexander Graf]

Am 27.06.2010 um 12:03 schrieb Avi Kivity <avi at redhat.com>:

> On 06/26/2010 02:24 AM, Alexander Graf wrote:
>> When running in hooked code we need a way to disable interrupts  
>> without
>> clobbering any interrupts or exiting out to the hypervisor.
>>
>> To achieve this, we have an additional critical field in the shared  
>> page. If
>> that field is equal to the r1 register of the guest, it tells the  
>> hypervisor
>> that we're in such a critical section and thus may not receive any  
>> interrupts.
>>
>>
>> --- a/arch/powerpc/kvm/book3s.c
>> +++ b/arch/powerpc/kvm/book3s.c
>> @@ -251,14 +251,25 @@ int kvmppc_book3s_irqprio_deliver(struct  
>> kvm_vcpu *vcpu, unsigned int priority)
>>      int deliver = 1;
>>      int vec = 0;
>>      ulong flags = 0ULL;
>> +    ulong crit_raw = vcpu->arch.shared->critical;
>> +    ulong crit_r1 = kvmppc_get_gpr(vcpu, 1);
>> +    bool crit;
>> +
>> +    /* Truncate crit indicators in 32 bit mode */
>> +    if (!(vcpu->arch.shared->msr&  MSR_SF)) {
>> +        crit_raw&= 0xffffffff;
>> +        crit_r1&= 0xffffffff;
>> +    }
>> +
>> +    crit = (crit_raw == crit_r1);
>>
>
> I think you need to qualify that for supervisor mode only.   
> Otherwise guest userspace can guess the value of shared->critical  
> and disable interrupts.


Yes, you're right. Good catch!

Alex

>