Re: [Xen-devel] [PATCH 03/14] xen/x86: Make mfn_to_gfn typesafe

[Julien Grall <julien.grall@xxxxxxx>]

On 10/05/2019 14:24, Jan Beulich wrote:
> > > > On 10.05.19 at 15:02, <julien.grall@xxxxxxx> wrote:
> > On 10/05/2019 12:35, Jan Beulich wrote:
> > > > > > On 07.05.19 at 17:14, <julien.grall@xxxxxxx> wrote:
> > > > --- a/xen/arch/x86/mm/shadow/common.c
> > > > +++ b/xen/arch/x86/mm/shadow/common.c
> > > > @@ -474,7 +474,8 @@ static inline void trace_resync(int event, mfn_t gmfn)
> > > >        if ( tb_init_done )
> > > >        {
> > > >            /* Convert gmfn to gfn */
> > > > -        unsigned long gfn = mfn_to_gfn(current->domain, gmfn);
> > > > +        unsigned long gfn = gfn_x(mfn_to_gfn(current->domain, gmfn));
> > > > +
> > > >            __trace_var(event, 0/*!tsc*/, sizeof(gfn), &gfn);
> > > >        }
> > > Can't you use gfn_t here, and hence avoid the gfn_x()? Same again further
> > > down.
> > Because __trace_var will export the value to the guest. I wasn't sure
> > whether we
> > can safely consider that gfn_t is exactly the same as unsigned long in
> > debug-build.
> Hmm, well - see the definition of gfn_t. George, what do you think?
I know what's the current definition. My point is we never made that assumption 
before. In all honesty, sure assumption would definitely help in a few places, 
but I think we ought to safeguard with BUILD_BUG(...).
Cheers,

--
Julien Grall

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