linux-kernel - Re: [PATCH] x86: x86_{phys,virt}

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Date:	Tue, 9 Sep 2008 09:31:53 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jan Beulich <jbeulich@...ell.com>
Cc:	Yinghai Lu <yhlu.kernel@...il.com>, tglx@...utronix.de,
	linux-kernel@...r.kernel.org, hpa@...or.com
Subject: Re: [PATCH] x86: x86_{phys,virt}_bits field also for i386 (v2)


* Jan Beulich <jbeulich@...ell.com> wrote:

> >>> Ingo Molnar <mingo@...e.hu> 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 
only.

	Ingo
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