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Date: Sun, 09 Sep 2012 10:01:33 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: mtd: kernel BUG at arch/x86/mm/pat.c:279!
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On 09/09/2012 08:31 AM, Linus Torvalds wrote:
> On Sun, Sep 9, 2012 at 7:56 AM, Suresh Siddha <suresh.b.siddha@intel.com> wrote:
>>
>> yes but that is not a valid range I think because of the supported
>> physical address bit limits of the processor and also the max
>> architecture limit of 52 address bits.
>
> But how could the caller possibly know that? None of those internal
> PAT limits are exposed anywhere.
>
> So doing the BUG_ON() is wrong. I'd suggest changing it to an EINVAL.
>
> In fact, BUG_ON() is *always* wrong, unless it's a "my internal data
> structures are so messed up that I cannot continue".
>

I suspect the right answer is doing something like:

	u64 max_phys = 1ULL << boot_cpu_data.x86_phys_bits;

	if (start >= max_phys || end > max_phys || start >= end)
		return -EINVAL;

... although max_phys perhaps should be precalculated and stored in 
struct cpuinfo_x86 instead of being generated de novo.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.