Re: [PATCH 3/4] [PATCH] kvmclock: allow it to be turned off

[Glauber Costa <gcosta@redhat.com>]

Avi Kivity wrote:
> Glauber Costa wrote:
>> Use the lower 3 lower bits of the system time msr to turn off the clock.
>> This means that all clock registration has to be aligned in a 4-byte 
>> boundary
>>
>>   
> 
> 3 bits -> 8 bytes.
dohh!! true
/me ashamed.

> How about just using just bit 0 as an enable bit (not a disable bit).  
> That means the default value of zero means the clock is disabled, and 
> that we have a couple of more bits to enable future features.

Apart from the fact that it will break every single guest out there, 
that's ok. As I said: these things are so early, that maybe we can pay 
this price. Your call.

>> Signed-off-by: Glauber Costa <gcosta@redhat.com>
>> ---
>>  arch/x86/kvm/x86.c |    5 +++++
>>  1 files changed, 5 insertions(+), 0 deletions(-)
>>
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 6abd784..7ce14ce 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -591,6 +591,11 @@ int kvm_set_msr_common(struct kvm_vcpu *
>>          if (vcpu->arch.time_page)
>>              kvm_release_page_dirty(vcpu->arch.time_page);
>>  
>> +        /* 4-byte unaligned accesses are invalid */
>> +        if (data & 0x7) {
>> +            vcpu->arch.time_page = NULL;
>> +            break;
>> +        }
>>          vcpu->arch.time = data & PAGE_MASK;
>>          vcpu->arch.time_offset = data & ~PAGE_MASK;
>>  
>>   
> 
> 


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