Re: [Xen-ia64-devel] Strange problem with virtual aliases

[Matthew Chapman <matthewc@xxxxxxxxxxxxxxx>]

Anthony,

> Did you access 0xfbdf7038 in guest physical mode?

No, the guest is in virtual mode (it=dt=rt=1).  (In fact, that mapping
has been inserted from the alt_dtlb_miss handler in my OS.)

> Seems domU only support identity mapping in region 0.

The DomU is only configured with 128MB of RAM, so 0xfbdf7038 would be
too high, Xen should print errors if doing identity mapping...  Also, I
have a number of other mappings in region 0 that seem to work correctly.

But thank you for the observation, the special treatment of region 0 may
be part of the reason.

Matt

> > 
> > tpa from inside the domain "proves" that the mappings are aliases:
> > 
> > tpa(0x2000000002500038) = 0x2500038
> > tpa(0xfbdf7038) = 0x2500038
> > 
> > However reading the data shows they are not:
> > 
> > *(0x2000000002500038) = 0x2000000001
> > *(0xfbdf7038) = 0
> > 
> > The real hardware TLB indeed has different physical addresses for the
> > two pages:
> > 
> > #                     VA            PA     RID    KEY   PS MA  ATTR  
> > PL PERMS 14 V A   00000000fbdf7000 0000017309000 000008 000000   4K
> > WB  p a d     2 rwrwrw-- 69 V A   2000000002500000 0000017c00000
> >                           010008 000000   4K WB  p a d     2 rwrwrw--
> > ^^^^^^^^^^^^^ 
> > 
> > Before I spend more time delving through Xen, does anyone have any
> > ideas 
> > how this could have happened?
> > 
> > N.B. I've compiled Xen with 4KB page size which may or may not be
> > relevant...  most likely not since Xenlinux runs fine.
> > 
> > Matt
> > 

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