Re: hypercall_xlat_continuation()

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

Mukesh Rathor wrote:
> 
> 
> 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
> 

yeah, looks like privcmd_ioctl_32() only fixes the wrapper struct. The
PFN array still is 32bit pfn's, and privcmd_ioctl() expects 64bits. So,
in a dilemma now, not sure if I should fix it up in privcmd_ioctl_32()
or change privcmd_ioctl() which will take some time to reverse engineer.
Not sure how many things I'll discover, if it's too many, it may
not be worth it in the end.

Thanks,
Mukesh