Re: [Xen-devel] hypercall_xlat_continuation()

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

Ian Campbell wrote:
> On Sat, 2009-05-23 at 06:17 -0400, Keir Fraser wrote:
> > On 22/05/2009 22:58, "Mukesh Rathor" <mukesh.rathor@xxxxxxxxxx> wrote:
> >
> > > Ok. Even if I can't make it clearer, at least I'll add few lines of comments
> > > explaining what's going on, after (and if) I figure it out.
> > >
> > > Jan,
> > >
> > > It seems assumption is made that a 64bit dom0 will not have a 32bit app making
> > > hypercall?
> > >
> > > BUG_ON(*reg != (unsigned int)*reg);  <====
> > You know that all the 'xlat' stuff in Xen is for 32-bit guests running on
> > 64-bit hypervisor, right? 64-bit dom0 would never execute this logic.
> It's worth noting though that I don't believe a 32 bit dom0 toolstack on
> a 64 bit kernel on a 64 bit hypervisor will work. In particular the
> privcmd "make a hypercall" ioctl doesn't do any compat translation so 32
> bit xend and friends can't make hypercalls that way and I think the
> MMAPBATCH privcmd doesn't work either.
>
> I'm sure there are other cases too (blktap user<->kernel ring layout
> maybe?).
>
> Ian.
Thanks Ian for good explanation of hypercall_xlat_continuation().

yeah, I'm just exploring that right now. There is MMAPBATCH_32, btw, in
dom0 that looks like was implemented by PPC folks. Also, MMAP_32.
I was able to start PV guest without network. Not sure if that was
because of compatibility or some other issue. I'm just looking at MMAP
stuff right now, think I finally figured out the chain of calls from
libxc to hyp to dom0 ... ia32_sys_call_table to compat_sys_ioctl to
handler to do_ioctl32_pointer .. whew!!

Thanks,
Mukesh




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