Re: [PATCH] libxc: x86: ensure that the initial mapping fits into the guest's memory

[Ian Campbell <Ian.Campbell@citrix.com>]

On Mon, 2013-01-07 at 10:35 +0000, Jan Beulich wrote:
> >>> On 07.01.13 at 08:00, Jan Beulich wrote:
> >>>> Ian Campbell <Ian.Campbell@citrix.com> 01/04/13 5:53 PM >>>
> >>libxc: x86: ensure that the initial mapping fits into the guest's memory
> >>
> >>In particular we need to check that adding 512KB of slack and
> >>rounding up to a 4MB boundary do not overflow the guest's memory
> >>allocation. Otherwise we run off the end of the p2m when building the
> >>guest's initial page tables and populate them with garbage.
> > 
> > Sadly our testing found this to cause SLE11 SP2 PV guests to not start
> > anymore (in its 4.1.x backported incarnation). I didn't get around yet to
> > check whether in the (apparently trivial) backport I overlooked something;
> > will do as soon as I get to the office.
> 
> Switching the added panic invocation to
> 
>             xc_dom_panic(dom->xch, XC_OUT_OF_MEMORY,
>                          "%s: not enough memory for initial mapping (%#"PRIx64" > %#"PRIpfn")",
>                          __FUNCTION__, try_virt_end >> PAGE_SHIFT_X86,
>                          dom->total_pages);
> 
> I see (with xend on 4.1.3)
> 
> xc: error: panic: xc_dom_x86.c:100: count_pgtables: not enough memory for initial mapping (0xffffffff81bff > 0x80000): Out of memory
> 
> Did this really work for you?

It did but I must confess I only tested with the mini-os test domain,
since that was what the initial bug was reported about and I stupidly
didn't think to test with a "real" kernel.

>  The 4.1.3 xl doesn't really want to work
> for me, so I can't directly cross check whether there's a behavioral
> difference between the two, but looking at an older log the virtual
> addresses reported for virt_alloc_end look similar. Afaict you need
> to subtract dom->parms.virt_base from try_virt_end.

I bet virt_base == 0 for the mini-os kernel I tried. I'll respin and
retest.

Thanks and sorry for the cockup,

Ian.