RE: [EXTERNAL] [PATCH v7 8/9] x86/time: add a domain context record for tsc_info...

[Paul Durrant <xadimgnik@xxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich <jbeulich@xxxxxxxx>
> Sent: 26 August 2020 15:03
> To: Paul Durrant <paul@xxxxxxx>
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; Durrant, Paul <pdurrant@xxxxxxxxxxxx>; 
> Ian Jackson
> <ian.jackson@xxxxxxxxxxxxx>; Wei Liu <wl@xxxxxxx>; Andrew Cooper 
> <andrew.cooper3@xxxxxxxxxx>; George
> Dunlap <george.dunlap@xxxxxxxxxx>; Julien Grall <julien@xxxxxxx>; Stefano 
> Stabellini
> <sstabellini@xxxxxxxxxx>; Roger Pau Monné <roger.pau@xxxxxxxxxx>
> Subject: RE: [EXTERNAL] [PATCH v7 8/9] x86/time: add a domain context record 
> for tsc_info...
> 
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> 
> On 18.08.2020 12:30, Paul Durrant wrote:
> > --- a/xen/include/public/save.h
> > +++ b/xen/include/public/save.h
> > @@ -93,7 +93,18 @@ struct domain_shared_info_context {
> >
> >  DECLARE_DOMAIN_SAVE_TYPE(SHARED_INFO, 2, struct 
> > domain_shared_info_context);
> >
> > -#define DOMAIN_SAVE_CODE_MAX 2
> > +#if defined(__i386__) || defined(__x86_64__)
> > +struct domain_tsc_info_context {
> > +    uint32_t mode;
> > +    uint32_t incarnation;
> > +    uint64_t elapsed_nsec;
> > +    uint32_t khz;
> > +};
> 
> sizeof() for this struct varies between 32-bit and 64-bit - is
> this not a problem? (alignof() varies too, but there I think
> it's indeed not a problem, albeit it could still be taken care
> of by using uint64_aligned_t, alongside the addition of an
> explicit padding field).

I don't think it should matter because domain context records have implicit 
padding to align up to the next 64-bit boundary, so as long as fields within 
the struct don't move (which I think is true in this case) then we should be ok.

  Paul

> 
> Jan