Re: [Xen-devel] [PATCH 4/5] xen/vm_event: Deny MSR writes if refused by vm_event reply

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 08.05.15 at 19:05, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
> On 05/08/2015 07:23 PM, Jan Beulich wrote:
>>>>> On 06.05.15 at 19:12, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
>>> --- a/xen/include/asm-x86/domain.h
>>> +++ b/xen/include/asm-x86/domain.h
>>> @@ -518,6 +518,11 @@ struct arch_vcpu
>>>          struct vm_event_emul_read_data emul_read_data;
>>>      } vm_event;
>>>  
>>> +    struct {
>>> +        bool_t do_write;
>>> +        uint64_t msr;
>>> +        uint64_t value;
>>> +    } msr_write;
>>>  };
>> 
>> Again a growth of struct vcpu by 24 bytes for everyone even though
>> quite likely only very few VMs would actually need this. To be honest
>> I'd even be hesitant to accept a pointer addition here. Perhaps this
>> should be a suitably sized, dynamically allocated array hanging off of
>> struct domain?
> 
> Sorry, I don't follow the dynamically allocated _array_ part. Could you
> please give a small example of what you mean?

Have a pointer in struct arch_domain which gets populated only
when needed, and if so by an array allocation with the array
dimension being the maximum number of vCPU-s the domain may
have. That way the memory overhead for non-monitored domains
is a pointer per domain (as opposed to quite a bit more unused
space per vCPU).

Jan


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