Re: hypercall_xlat_continuation()

[Mukesh Rathor <mukesh.rathor@oracle.com>]

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@oracle.com> 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