linux-kernel - Re: [PATCH v1 03/13] powerpc/mm/32s: rework mmu_mapin

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Date:   Tue, 18 Dec 2018 15:07:14 +0100
From:   Jonathan Neuschäfer <j.neuschaefer@....net>
To:     Christophe Leroy <christophe.leroy@....fr>
Cc:     Jonathan Neuschäfer <j.neuschaefer@....net>,
        linuxppc-dev@...ts.ozlabs.org, Paul Mackerras <paulus@...ba.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 03/13] powerpc/mm/32s: rework mmu_mapin_ram()

On Tue, Dec 18, 2018 at 09:18:42AM +0000, Christophe Leroy wrote:
> The only difference I see then are the flags. Everything else is seems
> identical.
> 
> I know you tried already, but would you mind trying once more with the
> following change ?
> 
[...]
> -		setbat(idx, PAGE_OFFSET + base, base, size, PAGE_KERNEL_TEXT);
> +		setbat(idx, PAGE_OFFSET + base, base, size, PAGE_KERNEL_X);

Good call, with this workaround on top of patches 1-3, it boots again:

	# mount -t debugfs d /sys/kernel/debug
	# cat /sys/kernel/debug/powerpc/block_address_translation
	---[ Instruction Block Address Translation ]---
	0: 0xc0000000-0xc0ffffff 0x00000000 Kernel EXEC
	1:         -
	2: 0xc1000000-0xc17fffff 0x01000000 Kernel EXEC
	3:         -
	4: 0xd0000000-0xd1ffffff 0x10000000 Kernel EXEC
	5:         -
	6:         -
	7:         -

	---[ Data Block Address Translation ]---
	0: 0xc0000000-0xc0ffffff 0x00000000 Kernel RW
	1: 0xfffe0000-0xffffffff 0x0d000000 Kernel RW no cache guarded
	2: 0xc1000000-0xc17fffff 0x01000000 Kernel RW
	3:         -
	4: 0xd0000000-0xd1ffffff 0x10000000 Kernel RW
	5:         -
	6:         -
	7:         -

> I think we may have some code trying to modify the kernel text without using
> code patching functions.

Is there any faster way than to sprinkle some printks in setup_kernel
and try to find the guilty piece of code this way?


Jonathan

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