Re: Xen 3.3: Problem HVM guest

[Christoph Egger <Christoph_Egger%gmx.de@localhost>]

Michael Litchard wrote:
> Christoph, how did you isolate the problem? I'll take any opportunity
> to learn more troubleshooting techniques.

Launch xend by hand with 'trace_start' instead of 'start'. Then you get
a /var/log/xen/xend.trace file. Look at it how far it comes there and 
find the python routine. I figured out, it stopped running further when
it calls xc.build_hvm() from the lowlevel/xs python module which in turn
calls xc_build_hvm() in tools/libxc/xc_hvm_build.c. With debug printf's,
I tracked it down to what I have shown here.

>           Michael
>
> On Tue, Aug 12, 2008 at 2:54 PM, Christoph Egger 
> <Christoph_Egger%gmx.de@localhost> wrote:
> > Christoph Egger wrote:
> > > Hi,
> > >
> > > When launching a HVM guest, the process hangs and does not even block any
> > > xmlrpc communication, there's a significant system slowdown until reboot.
> > >
> > > I finally indentified the place of hang. It is in the xentools33 package
> > > in ${WRKSRC}/libxc/xc_hvm_build.c , function setup_guest().
> > >
> > > At the end of setup_guest(), there's this junk of code:
> > >
> > >
> > >
> > >    /* Insert JMP <rel32> instruction at address 0x0 to reach entry point.
> > > */
> > >    entry_eip = elf_uval(&elf, elf.ehdr, e_entry);
> > >    if ( entry_eip != 0 )    {
> > >        char *page0 = xc_map_foreign_range(
> > >            xc_handle, dom, PAGE_SIZE, PROT_READ | PROT_WRITE, 0);
> > >        if ( page0 == NULL )
> > >            goto error_out;
> > >        page0[0] = 0xe9;               <------------ "hang"
> > >        *(uint32_t *)&page0[1] = entry_eip - 5;
> > >        munmap(page0, PAGE_SIZE);
> > >    }
> > >
> > >
> > > The "hang" happens when executing page0[0] = 0xe9;
> > >
> > > I'm CC this to tech-kern, because I'm not sure if this is a bug in
> > > xentools or if I found a UVM/pmap bug.
> > Here is an URL to the diff where this hunk has been added including the
> > commit log:
> >
> > http://xenbits.xensource.com/xen-unstable.hg/rev/772674585a1a