Re: Linux 4.4 MW: Boot under Xen fails with CONFIG_DEBUG_WX enabled: RIP: ptdump_walk_pgd_level_core

[Sander Eikelenboom <linux@eikelenboom.it>]

On 2015-11-04 19:06, Ingo Molnar wrote:
> * Stephen Smalley <sds@tycho.nsa.gov> wrote:
> 
>> On 11/04/2015 06:55 AM, Sander Eikelenboom wrote:
>> >Hi All,
>> >
>> >I just tried to boot with the current linus mergewindow tree under Xen.
>> >It fails with a kernel panic at boot with the new "CONFIG_DEBUG_WX"
>> >option enabled.
>> >Disabling it makes the kernel boot fine.
>> >
>> >The splat:
>> >[   18.424241] Freeing unused kernel memory: 1104K (ffffffff822fc000 -
>> >ffffffff82410000)
>> >[   18.430314] Write protecting the kernel read-only data: 18432k
>> >[   18.441054] Freeing unused kernel memory: 1144K (ffff880001ae2000 -
>> >ffff880001c00000)
>> >[   18.447966] Freeing unused kernel memory: 1560K (ffff88000207a000 -
>> >ffff880002200000)
>> >[   18.453947] BUG: unable to handle kernel paging request at
>> >ffff88055c883000
>> >[   18.459943] IP: [<ffffffff8105af8e>]
>> >ptdump_walk_pgd_level_core+0x20e/0x440
>> >[   18.465847] PGD 2212067 PUD 0
>> >[   18.471564] Oops: 0000 [#1] SMP
>> >[   18.477248] Modules linked in:
>> >[   18.482918] CPU: 2 PID: 1 Comm: swapper/0 Not tainted
>> >4.3.0-mw-20151104-linus-doflr+ #1
>> >[   18.488804] Hardware name: MSI MS-7640/890FXA-GD70 (MS-7640)  , BIOS
>> >V1.8B1 09/13/2010
>> >[   18.494778] task: ffff880059b90000 ti: ffff880059b98000 task.ti:
>> >ffff880059b98000
>> >[   18.500852] RIP: e030:[<ffffffff8105af8e>]  [<ffffffff8105af8e>]
>> >ptdump_walk_pgd_level_core+0x20e/0x440
> 
> It would be nice to see which line of code this corresponds to. Doing 
> this:
> 
>   gdb vmlinux
>   list *0xffffffff8105af8e
> 
> should normally do the trick.
> 
> Thanks,
> 
> 	Ingo

Hi Ingo,

(gdb) list *0xffffffff8105af8e
0xffffffff8105af8e is in ptdump_walk_pgd_level_core 
(arch/x86/mm/dump_pagetables.c:181).
warning: Source file is more recent than executable.
176	 * On 64 bits, sign-extend the 48 bit address to 64 bit
177	 */
178	static unsigned long normalize_addr(unsigned long u)
179	{
180	#ifdef CONFIG_X86_64
181		return (signed long)(u << 16) >> 16;
182	#else
183		return u;
184	#endif
185	}

--
Sander