RE: [Xen-ia64-devel] RE: vcpu_translate issue

["Magenheimer, Dan (HP Labs Fort Collins)" <dan.magenheimer@xxxxxx>]

Hmmm... by changing the metaphysical address handling code
in vcpu_translate, I seem to have uncovered a latent bug:
Sometimes vcpu_translate is being called with a virtual
address even though the domain is in metaphysical mode.
Previously these were incorrectly(?) just direct mapped.

Rather than back out the changes, I have changed the panic
to a printk.  If you see some "vcpu_translate: bad physical
address" messages, don’t be surprised, but you can ignore
it unless you want to help track down and fix the problem.

Mmap09 is not printing this message so the problem is
(apparently) unrelated.

Dan

> -----Original Message-----
> From: xen-ia64-devel-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-ia64-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf 
> Of Magenheimer, Dan (HP Labs Fort Collins)
> Sent: Wednesday, November 09, 2005 11:29 AM
> To: Xu, Anthony
> Cc: xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
> Subject: [Xen-ia64-devel] RE: vcpu_translate issue
> 
> FYI, in case anyone else might look at this:
> 
> I made a fix so that vcpu_translate supports region0
> (and doesn't print out the message), but ltp-mmap09
> still doesn't work (goes into a silent infinite loop).
> 
> I don't have access to a hardware debugger right
> now so have committed the change in case anyone
> else is able to look at mmap09 in more detail.
> 
> Dan
> 
> > -----Original Message-----
> > From: Xu, Anthony [mailto:anthony.xu@xxxxxxxxx] 
> > Sent: Friday, November 04, 2005 11:56 PM
> > To: Magenheimer, Dan (HP Labs Fort Collins)
> > Cc: xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
> > Subject: RE: vcpu_translate issue
> > 
> > Dan,
> > 
> > I just want to run some testcases like ltp to make dom0 more 
> > stable. If this is the case I have no choice but to defer 
> those tests.
> > 
> > 
> > Thanks
> > Anthony
> > 
> > >-----Original Message-----
> > >From: Magenheimer, Dan (HP Labs Fort Collins) 
> > [mailto:dan.magenheimer@xxxxxx]
> > >Sent: 2005年11月4日 22:13
> > >To: Xu, Anthony
> > >Cc: xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
> > >Subject: RE: vcpu_translate issue
> > >
> > >The warning is there because the current code doesn't yet
> > >work properly for a region 0 virtual address.  Even
> > >if you remove the printf, I don't think ltp mmap09 will
> > >work properly because the current code assumes
> > >incorrectly that every region 0 access is a guest
> > >physical access.  Bug!  I think this is the first time
> > >we have seen a region 0 virtual address.
> > >
> > >Also, the printf is very good at catching problems when
> > >there is a new bug in Xen so it would be nice to
> > >keep the printf.  Perhaps it could be tied to a
> > >Xen command line option: warnregion0.  E.g.
> > >
> > >if (metaphysical) {
> > >   if (address >> 61)
> > >           panic_domain(("bad metaphysical address")
> > >   else {
> > >           ... existing phys translate code
> > >   }
> > >{
> > >else if (!(address >> 61) && warnregion0) {
> > >   printf
> > >}
> > >
> > >I think this code will also fix region 0 virtual addresses
> > >(because it properly falls through to the rest of
> > >vcpu_translate).
> > >
> > >> -----Original Message-----
> > >> From: Xu, Anthony [mailto:anthony.xu@xxxxxxxxx]
> > >> Sent: Friday, November 04, 2005 3:20 AM
> > >> To: Magenheimer, Dan (HP Labs Fort Collins)
> > >> Cc: xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
> > >> Subject: vcpu_translate issue
> > >>
> > >> Dan,
> > >>
> > >> In vcpu_translate function, if guest address is within region
> > >> 0 and guest is in virtual mode, vcpu_translate will print
> > >> warning message and don't translate. It seems you assume
> > >> guest will not access this kind of address, but actually
> > >> guest application can allocate region 0 address spaces by
> > >> using system call mmap.
> > >>
> > >> You can try testcase mmap09 of ltp on both native and xen0 to
> > >> find out this.
> > >>
> > >> So, Can we remove this code segment in vcpu_translate?
> > >>
> > >> Thanks,
> > >> Anthony.
> > >>
> > >>
> > 
> 

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