Re: [Xen-ia64-devel] EFI Mapping Windows Install Crash Bug

[Isaku Yamahata <yamahata@xxxxxxxxxxxxx>]

On Tue, Jul 01, 2008 at 11:03:28AM +1000, Simon Horman wrote:
> Hi,
> 
> I'm a bit hesitant to jump the gun, but I think that I might have
> isolated the cause of win2k3-sp2 crashing during install when my EFI
> Mapping patches are applied. Well, perhaps not the cause, but I think I
> know where it is dying.
> 
>     Quickly as background, the EFI Mapping parches move the mapping
>     that EFI is taught on boot time to map memory where Linux places
>     it ( basically pa + (0xe<60) ) instead of where Xen usually
>     places it ( basically pa + (0xf<60) ). In order to protect this
>     mapping from HVM domains a special region id is used. The
>     hypervisor switches to that region id just before making any
>     PAL, SAL or EFI calls, and switches back to the previous region
>     id once the call completes.  As region 7 has to be changed,
>     entries that are pinned into the TLB have to be repinned. And
>     that is roughly where the fun begins.
> 
> As for the problem? It seems to be caused by ia64_mca_cpe_int_caller()
> calling ia64_log_queue() which calls ia64_sal_get_state_info(). I
> believe that the hypervisor dies in ia64_log_queue() somewhere after
> ia64_sal_get_state_info() completes. That is, I am suspecting that the
> call to ia64_sal_get_state_info() is returning bogus data.

Is ia64_mca_cpe_int_caller() called in interrupt context?
If so, ia64_log_queue() calls xmalloc() which can't be called
from interrupt context. Then xen VMM crashes at ASSERT(!in_irq())
in _xmalloc().


> Furthermore, my traces seem to indicate that the problem arises the
> call to ia64_log_queue() and in turn to ia64_sal_get_state_info() is
> made when the region id is already switched to make some other PAL, SAL
> or EFI call (though I doubt it is particularly important which one).
> 
> This seems to make sense to me as ia64_mca_cpe_int_caller() is
> "Triggered by sw interrupt from CPE polling routine.".
> 
> I am unsure about what to do about this problem, but for testing
> purposes I simply removed the call to ia64_log_queue() from
> ia64_mca_cpe_int_caller() and things seem to work.
> 
> When I say seem to work, this bug does not manifest every time I install
> win2k3-sp2. So it can be hard to tell if a change has improved things or
> not. But for now, I have not seen a crash occur with this hack in place
> (+ various other changes which may or may not be relevant, but this one
> seems to be particularly important).
> 
> I will investigate my theory that things die in ia64_log_queue()
> further. But I wonder if there might be a way to permanently remove/move
> the call to ia64_log_queue() out of ia64_mca_cpe_int_caller() and
> possibly other PAL, SAL or EFI calls inside other MCA code.
> 

-- 
yamahata

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