Re: [Xen-devel] [PATCH 2/2] xen: add update indicator to vcpu_runstate_info

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 20 May 2016, Jan Beulich wrote:
> >>> On 20.05.16 at 17:54, <JGross@xxxxxxxx> wrote:
> > On 20/05/16 17:36, Jan Beulich wrote:
> >>>>> On 20.05.16 at 17:04, <JGross@xxxxxxxx> wrote:
> >>> On 20/05/16 16:49, Jan Beulich wrote:
> >>>>>>> On 20.05.16 at 15:22, <JGross@xxxxxxxx> wrote:
> >>>>>      if ( guest_handle_is_null(runstate_guest(v)) )
> >>>>>          return 1;
> >>>>>  
> >>>>> +    update_flag = VM_ASSIST(v->domain, runstate_update_flag);
> >>>>> +
> >>>>>      smap_policy = smap_policy_change(v, SMAP_CHECK_ENABLED);
> >>>>>  
> >>>>> +    if ( update_flag )
> >>>>> +    {
> >>>>> +        off = offsetof(struct vcpu_runstate_info, state_entry_time) + 
> >>>>> 7;
> >>>>
> >>>> How come this is outside the following if()? Also sizeof(...) - 1 please
> >>>> instead of the literal 7.
> >>>
> >>> I'm using off for the source address in __raw_copy_to_guest(), too.
> >> 
> >> But the offset should, afaict, be different for 32-bit (x86) and
> >> 64-bit (or ARM).
> > 
> > Why? The offset is applied to v->runstate which clearly is the same
> > for 32 and 64 bit domains, as it is the hypervisor private structure.
> > Different offsets have to be applied at the destination side only, and
> > this is done properly (at least I think so).
> 
> But as you say you use the offset for two purposes: The use on
> the guest handle is which is problematic; the use on the hypervisor
> internal structure is of course fine.

The code is a bit ugly, but it looks like it would work on ARM

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