[PATCH lucid] UBUNTU: SAUCE: dove: avoid page table overwrite when resuming from hibernation

[Eric Miao]

On Sat, Apr 24, 2010 at 12:40 AM, John Johansen
<john.johansen at canonical.com> wrote:
> On 04/23/2010 07:18 AM, Stefan Bader wrote:
>> Eric Miao wrote:
>>> BTW, this may apply to other ARM variants as well, but the hibernation
>>> feature should really be made common first of all in that sense.
>>>
>>> commit 1f3ebd28c0e8adf7f7a1fc85377a57d8dbc56267
>>> Author: Eric Miao <eric.miao at canonical.com>
>>> Date:   Fri Apr 23 14:16:17 2010 +0800
>>>
>>>     UBUNTU: SAUCE: dove: avoid page table overwrite when resuming from
>>> hibernation
>>>
>>>     BugLink: http://bugs.launchpad.net/bugs/509006
>>>
>>>     Resuming from hibernation is OK if 'resume=/dev/sdaX' is explicitly
>>>     specified on the kernel command line, but it fails if scripts in
>>>     initramfs are used to trigger the resume. It turned out to be page
>>>     table being overwritten when restoring the memory content because
>>>     it's using a normal user process's page table in the latter case,
>>>     which is not safe and could be overwritten. Fix this by using the
>>>     safe swapper_pg_dir during restoring.
>>>
>>>     Signed-off-by: Eric Miao <eric.miao at canonical.com>
>>>
>>> diff --git a/arch/arm/mach-dove/Makefile b/arch/arm/mach-dove/Makefile
>>> index 0be1e1c..c5c028f 100755
>>> --- a/arch/arm/mach-dove/Makefile
>>> +++ b/arch/arm/mach-dove/Makefile
>>> @@ -1,3 +1,5 @@
>>> +AFLAGS_swsusp.o                     := -DTEXT_OFFSET=$(TEXT_OFFSET)
>>> +
>>>  obj-y                               += clock.o common.o addr-map.o irq.o pcie.o mpp.o \
>>>                              sdhci_cam_mbus.o
>>>  obj-$(CONFIG_MACH_DOVE_RD_AVNG)     += dove-rd-avng-setup.o
>>> diff --git a/arch/arm/mach-dove/swsusp.S b/arch/arm/mach-dove/swsusp.S
>>> index 4f4a884..8e308d8 100644
>>> --- a/arch/arm/mach-dove/swsusp.S
>>> +++ b/arch/arm/mach-dove/swsusp.S
>>> @@ -28,6 +28,7 @@
>>>   */
>>>
>>>  #include <linux/linkage.h>
>>> +#include <asm/memory.h>
>>>  #include <asm/segment.h>
>>>  #include <asm/page.h>
>>>  #include <asm/asm-offsets.h>
>>> @@ -209,8 +210,14 @@ FUNC(swsusp_arch_suspend)
>>>
>>>  FUNC_END(swsusp_arch_suspend)
>>>
>>> +#define KERNEL_RAM_PADDR    (PHYS_OFFSET + TEXT_OFFSET)
>>> +
>>>  FUNC(swsusp_arch_resume)
>>>      /* set page table if needed */
>>> +    ldr     r0, =(KERNEL_RAM_PADDR - 0x4000)
>>> +    mcr     p15, 0, r0, c2, c0, 0           @ load page table pointer
>>> +    mcr     p15, 0, r0, c8, c7, 0           @ invalidate I,D TLBs
>>> +    mcr     p15, 0, r0, c7, c5, 4           @ ISB
>>>
>>>      /*
>>>       * retore "nr_copy_pages" pages which are saved and specified
>>>
>> The patch probably is correct, but from the reviewing point of view I do not
>> know how I make the connection between swapper_pg_dir in the comment and the
>> patch itself. Is that only me?
>>
> No, I also would like to see a little more information.
>

Ah, sorry for the confusion. swapper_pg_dir is the initial page table for
ARM kernel, which is physically located at KERNEL_RAM_PADDR - 0x4000.
I should have made it clear by a macro or something. The following code is
excerpted from arch/arm/kernel/head.S:

/*
 * swapper_pg_dir is the virtual address of the initial page table.
 * We place the page tables 16K below KERNEL_RAM_VADDR.  Therefore, we must
 * make sure that KERNEL_RAM_VADDR is correctly set.  Currently, we expect
 * the least significant 16 bits to be 0x8000, but we could probably
 * relax this restriction to KERNEL_RAM_VADDR >= PAGE_OFFSET + 0x4000.
 */
#if (KERNEL_RAM_VADDR & 0xffff) != 0x8000
#error KERNEL_RAM_VADDR must start at 0xXXXX8000
#endif

	.globl	swapper_pg_dir
	.equ	swapper_pg_dir, KERNEL_RAM_VADDR - 0x4000

	.macro	pgtbl, rd
	ldr	\rd, =(KERNEL_RAM_PADDR - 0x4000)
	.endm