linux-kernel - Re: [Bug #11313] Plugging HDMI causes "unable to handle kernel paging request"

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Date:	Thu, 21 Aug 2008 19:56:24 +0100 (BST)
From:	Hugh Dickins <hugh@...itas.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
cc:	Rafał Miłecki <zajec5@...il.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Yinghai Lu <yhlu.kernel@...il.com>,
	Jack Steiner <steiner@....com>,
	Alan Jenkins <alan-jenkins@...fmail.co.uk>
Subject: Re: [Bug #11313] Plugging HDMI causes "unable to handle kernel paging
 request"

On Thu, 21 Aug 2008, Jeremy Fitzhardinge wrote:
> 
> >>>>
> Some notes as I pick through all the evidence so far:
> 
> - the crash is specifically because there are reserved bits set in the pmd
> - the pmd is b02a00043a6001a3 in both cases

Yes, it's corrupt, it should be
               800000013a6001a3

> - the vaddr is ffff88013a600000 in the first crash, and
>                ffff81013a6d1c00 in the second
>   corresponding to the same large-page pmd mapping of phys page 0x13a600000
> - this maps to e820 entry
>  BIOS-e820: 0000000100000000 - 0000000140000000 (usable)
> - the corresponding boot-time mapping is
> 
> init_memory_mapping
>  0100000000 - 0140000000 page 2M
> kernel direct mapping tables up to 140000000 @ b000-11000
>                                                ^^^^^^^^^^
> addr 100000000 reusing pgd 201880 0000000000202063
> last_map_addr: 140000000 end: 140000000
> 
> !!! and the memory allocated for this pagetable is:
>   #5 [0000008000 - 000000b000]          PGTABLE ==> [0000008000 - 000000b000]
>   #6 [000000b000 - 000000c000]          PGTABLE ==> [000000b000 - 000000c000]
>                                                      ^^^^^^^^^^^^^^^^^^^^^^^
> 
> IOW, it's mapping using b000-11000, but it has only reserved b000 - c000
> 
> Also, this is right in the middle of the ISA area, which seems risky.
> <<<<
> 
> Bug #11237 shows the same symptom, so I'm pretty confident they're dups now.

[ Sorry, I'm replying to #11313 even though we think it's dup of #11237. ]

Haven't you got that backwards?

My reading is that find_early_table_space set aside b000-11000 for the
worst case possible, but actually only b000-c000 was needed (because
most of the tables were already there): no problem.
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