Re: [PATCH] x86: x86_{phys,virt}_bits field also for i386 (v2)

From: Ingo Molnar
Date: Tue Sep 09 2008 - 03:32:22 EST

* Jan Beulich <jbeulich@xxxxxxxxxx> wrote:

> >>> Ingo Molnar <mingo@xxxxxxx> 08.09.08 20:54 >>>
> >
> >-tip testing found various kernel crashes on 32-bit testboxes and i've
> >bisected it down to:
> >
> >...
> >
> >a typical crash is like the one attached below. It's due to the ioremap
> >failing. The drivers/char/rio/rio_linux.c driver probes these addresses:
> >
> > static int rio_probe_addrs[] = { 0xc0000, 0xd0000, 0xe0000 };
> >
> >which is questionable ...
> No, they look absolutely valid, they're ISA ROM addresses.

yeah - questionable in the sense of assuming that it's all non-RAM. But
there's no better way to probe for ROMs i guess.

> > for now i've reverted it from current tip/master, see commit
> > e3fdd129901. (you can reinstate the commit by doing "git revert
> > e3fdd1299"
> >
> > Even if we decided to fail these ioremaps it would be better to emit
> > a warning instead of crashing the box.
> We shouldn't fail them, they're valid. What the crash means is that
> even addresses below 1Mb are considered out of range, which I can only
> take as x86_phys_bits being zero (or a bogus very small number) on
> secondary (or all) CPUs. However, looking at the call tree I can't see
> how that could happen (provided CPUID doesn't produce garbage output):
> - smp_store_cpu_info(), as it always did, pre-initializes the new CPU's
> info with boot_cpu_data, and calls identify_secondary_cpu()
> - identify_secondary_cpu() calls identify_cpu()
> - identify_cpu() pre-sets x86_phys_bits to 32, and since the field didn't
> exist for 32-bits before, nothing should be able to clear or otherwise
> alter it

there's nothing weird about this testbox (it's a usual whitebox) - and
two other testboxes failed as well after some time (no crashlog
available from them). A 64-bit testbox didnt fail so it seems 32-bit

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