Re: [PATCH 2/5] xen/vm_access: Support for memory-content hiding

[Razvan Cojocaru <rcojocaru@bitdefender.com>]

On 05/08/2015 07:07 PM, Jan Beulich wrote:
>> > --- a/xen/include/asm-x86/domain.h
>> > +++ b/xen/include/asm-x86/domain.h
>> > @@ -512,6 +513,7 @@ struct arch_vcpu
>> >          uint32_t emulate_flags;
>> >          unsigned long gpa;
>> >          unsigned long eip;
>> > +        struct vm_event_emul_read_data emul_read_data;
> Considering the size of this structure I don't think this should be
> there for all vCPU-s of all guests. IOW - please allocate this
> dynamically only on domains where it's needed.

Looking at the code, it's not immediately clear how to differentiate
between a domain where this is needed and one where it is not. At domain
init time we don't know, because it might become needed as soon as a
vm_event client becomes attached to the domain. Then again, even once a
vm_event client attaches to the domain, it might still not be necessary
to allocate that structure, as the client might never reply with
MEM_ACCESS_SET_EMUL_READ_DATA.

The only place where we know for sure that it's needed is in
p2m_mem_access_check(), when receiving a vm_event response with
MEM_ACCESS_SET_EMUL_READ_DATA (lazy allocation). Would this be alright?


Thanks,
Razvan