Re: [PATCH] [RESEND] arm: limit memblock base address for early_pte_alloc

Minchan Kim
2012-06-28T04:47:01Z

종성 선임님.

제가 장비가 없는 문제로 아래의 패치를 테스트 할 수 없는데, 시간 되시면
테스트 후 Nicolas에게 feedback좀 부탁드리겠습니다. 문제는 posting해놓고,
follow up하지 않게 되면,,,, 신뢰의 문제라서요. -_-;;

러쎌이 어떻게 나올지 모르겠네요. 계속 그냥 1M로 해서 쓰라고 할지...

감사합니다.

On 06/28/2012 01:33 PM, Nicolas Pitre wrote:

> On Wed, 27 Jun 2012, Dave Martin wrote:
>
>> On Tue, Jun 05, 2012 at 04:11:52PM +0900, Minchan Kim wrote:
>>> If we do arm_memblock_steal with a page which is not aligned with section size,
>>> panic can happen during boot by page fault in map_lowmem.
>>>
>>> Detail:
>>>
>>> 1) mdesc->reserve can steal a page which is allocated at 0x1ffff000 by memblock
>>> which prefers tail pages of regions.
>>> 2) map_lowmem maps 0x00000000 - 0x1fe00000
>>> 3) map_lowmem try to map 0x1fe00000 but it's not aligned by section due to 1.
>>> 4) calling alloc_init_pte allocates a new page for new pte by memblock_alloc
>>> 5) allocated memory for pte is 0x1fffe000 -> it's not mapped yet.
>>> 6) memset(ptr, 0, sz) in early_alloc_aligned got PANICed!
>>>
>>> This patch fix it by limiting memblock to mapped memory range.
>>>
>>> Reported-by: Jongsung Kim <neidhard.kim@lge.com>
>>> Suggested-by: Chanho Min <chanho.min@lge.com>
>>> Signed-off-by: Minchan Kim <minchan@kernel.org>
>>> ---
>>> arch/arm/mm/mmu.c | 37 ++++++++++++++++++++++---------------
>>> 1 file changed, 22 insertions(+), 15 deletions(-)
>>>
>>> diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
>>> index e5dad60..a15aafe 100644
>>> --- a/arch/arm/mm/mmu.c
>>> +++ b/arch/arm/mm/mmu.c
>>> @@ -594,7 +594,7 @@ static void __init alloc_init_pte(pmd_t *pmd, unsigned long addr,
>>>
>>> static void __init alloc_init_section(pud_t *pud, unsigned long addr,
>>> unsigned long end, phys_addr_t phys,
>>> - const struct mem_type *type)
>>> + const struct mem_type *type, bool lowmem)
>>> {
>>> pmd_t *pmd = pmd_offset(pud, addr);
>>>
>>> @@ -619,6 +619,8 @@ static void __init alloc_init_section(pud_t *pud, unsigned long addr,
>>>
>>> flush_pmd_entry(p);
>>> } else {
>>> + if (lowmem)
>>> + memblock_set_current_limit(__pa(addr));
>>
>> I thought of doing something similar to this. A concern I have is that
>> when mapping the first few sections, is it guaranteed that there will be
>> enough memory available below memblock.current_limit to allocate extra
>> page tables, in general? I think we could get failures here even though
>> there is spare (unmapped) memory above the limit.
>>
>> An alternative approach would be to install temporary section mappings
>> to cover all of lowmem before starting to create the real mappings.
>> The memblock allocator still knows which regions are reserved, so we
>> shouldn't end up scribbling on pages which are really not supposed to
>> be mapped in lowmem.
>>
>> That feels like it should work, but would involve extra overheads, more
>> flushing etc. to purge all those temporary section mappings from the TLB.
>
> This is all rather fragile and inelegant.
>
> I propose the following two patches instead -- both patches are included
> inline not to break the email thread. What do you think?
>
> ---------- >8
>
> From: Nicolas Pitre <nicolas.pitre@linaro.org>
> Date: Wed, 27 Jun 2012 23:02:31 -0400
> Subject: [PATCH] ARM: head.S: simplify initial page table mapping
>
> Let's map the initial RAM up to the end of the kernel.bss plus 64MB
> instead of the strict kernel image area. This simplifies the code
> as the kernel image only needs to be handled specially in the XIP case.
> This also give some room for the early memory allocator to use before
> the real mapping is finally installed with the actual amount of memory.
>
> Signed-off-by: Nicolas Pitre <nico@linaro.org>
>
> diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
> index 835898e7d7..cc3103fb66 100644
> --- a/arch/arm/kernel/head.S
> +++ b/arch/arm/kernel/head.S
> @@ -55,14 +55,6 @@
> add \rd, \phys, #TEXT_OFFSET - PG_DIR_SIZE
> .endm
>
> -#ifdef CONFIG_XIP_KERNEL
> -#define KERNEL_START XIP_VIRT_ADDR(CONFIG_XIP_PHYS_ADDR)
> -#define KERNEL_END _edata_loc
> -#else
> -#define KERNEL_START KERNEL_RAM_VADDR
> -#define KERNEL_END _end
> -#endif
> -
> /*
> * Kernel startup entry point.
> * ---------------------------
> @@ -218,51 +210,50 @@ __create_page_tables:
> blo 1b
>
> /*
> - * Now setup the pagetables for our kernel direct
> - * mapped region.
> + * Map some RAM to cover the kernel image and its .bss section.
> + * Push some additional 64MB to give the early memory allocator
> + * some initial room (beware: real RAM might or might not be there
> + * across the whole area). The real memory map will be established
> + * (extended or shrunk) later.
> */
> - mov r3, pc
> - mov r3, r3, lsr #SECTION_SHIFT
> - orr r3, r7, r3, lsl #SECTION_SHIFT
> - add r0, r4, #(KERNEL_START & 0xff000000) >> (SECTION_SHIFT - PMD_ORDER)
> - str r3, [r0, #((KERNEL_START & 0x00f00000) >> SECTION_SHIFT) << PMD_ORDER]!
> - ldr r6, =(KERNEL_END - 1)
> - add r0, r0, #1 << PMD_ORDER
> + add r0, r4, #PAGE_OFFSET >> (SECTION_SHIFT - PMD_ORDER)
> + ldr r6, =(_end + 64 * 1024 * 1024)
> + orr r3, r8, r7
> add r6, r4, r6, lsr #(SECTION_SHIFT - PMD_ORDER)
> -1: cmp r0, r6
> +1: str r3, [r0], #1 << PMD_ORDER
> add r3, r3, #1 << SECTION_SHIFT
> - strls r3, [r0], #1 << PMD_ORDER
> + cmp r0, r6
> bls 1b
>
> #ifdef CONFIG_XIP_KERNEL
> /*
> - * Map some ram to cover our .data and .bss areas.
> + * Map the kernel image separately as it is not located in RAM.
> */
> - add r3, r8, #TEXT_OFFSET
> - orr r3, r3, r7
> - add r0, r4, #(KERNEL_RAM_VADDR & 0xff000000) >> (SECTION_SHIFT - PMD_ORDER)
> - str r3, [r0, #(KERNEL_RAM_VADDR & 0x00f00000) >> (SECTION_SHIFT - PMD_ORDER)]!
> - ldr r6, =(_end - 1)
> - add r0, r0, #4
> +#define XIP_START XIP_VIRT_ADDR(CONFIG_XIP_PHYS_ADDR)
> + mov r3, pc
> + mov r3, r3, lsr #SECTION_SHIFT
> + orr r3, r7, r3, lsl #SECTION_SHIFT
> + add r0, r4, #(XIP_START & 0xff000000) >> (SECTION_SHIFT - PMD_ORDER)
> + str r3, [r0, #((XIP_START & 0x00f00000) >> SECTION_SHIFT) << PMD_ORDER]!
> + ldr r6, =(_edata_loc - 1)
> + add r0, r0, #1 << PMD_ORDER
> add r6, r4, r6, lsr #(SECTION_SHIFT - PMD_ORDER)
> 1: cmp r0, r6
> - add r3, r3, #1 << 20
> - strls r3, [r0], #4
> + add r3, r3, #1 << SECTION_SHIFT
> + strls r3, [r0], #1 << PMD_ORDER
> bls 1b
> #endif
>
> /*
> - * Then map boot params address in r2 or the first 1MB (2MB with LPAE)
> - * of ram if boot params address is not specified.
> + * Then map boot params address in r2 if specified.
> */
> mov r0, r2, lsr #SECTION_SHIFT
> movs r0, r0, lsl #SECTION_SHIFT
> - moveq r0, r8
> - sub r3, r0, r8
> - add r3, r3, #PAGE_OFFSET
> - add r3, r4, r3, lsr #(SECTION_SHIFT - PMD_ORDER)
> - orr r6, r7, r0
> - str r6, [r3]
> + subne r3, r0, r8
> + addne r3, r3, #PAGE_OFFSET
> + addne r3, r4, r3, lsr #(SECTION_SHIFT - PMD_ORDER)
> + orrne r6, r7, r0
> + strne r6, [r3]
>
> #ifdef CONFIG_DEBUG_LL
> #if !defined(CONFIG_DEBUG_ICEDCC) && !defined(CONFIG_DEBUG_SEMIHOSTING)
>
> ---------- >8
>
> From: Nicolas Pitre <nicolas.pitre@linaro.org>
> Date: Wed, 27 Jun 2012 23:58:39 -0400
> Subject: [PATCH] ARM: adjust the memblock limit according to the available memory mapping
>
> Early on the only accessible memory comes from the initial mapping
> performed in head.S, minus those page table entries cleared in
> prepare_page_table(). Eventually the full lowmem is available once
> map_lowmem() has mapped it. Let's have this properly reflected in the
> memblock allocator limit.
>
> Signed-off-by: Nicolas Pitre <nico@linaro.org>
>
> diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
> index e5dad60b55..7260e98dd4 100644
> --- a/arch/arm/mm/mmu.c
> +++ b/arch/arm/mm/mmu.c
> @@ -932,7 +932,6 @@ void __init sanity_check_meminfo(void)
> #endif
> meminfo.nr_banks = j;
> high_memory = __va(arm_lowmem_limit - 1) + 1;
> - memblock_set_current_limit(arm_lowmem_limit);
> }
>
> static inline void prepare_page_table(void)
> @@ -967,6 +966,13 @@ static inline void prepare_page_table(void)
> for (addr = __phys_to_virt(end);
> addr < VMALLOC_START; addr += PMD_SIZE)
> pmd_clear(pmd_off_k(addr));
> +
> + /*
> + * The code in head.S has set a mapping up to _end + 64MB.
> + * The code above has cleared any mapping from 'end' upwards.
> + * Let's have this reflected in the available memory from memblock.
> + */
> + memblock_set_current_limit(min(end, virt_to_phys(_end) + SZ_64M));
> }
>
> #ifdef CONFIG_ARM_LPAE
> @@ -1113,6 +1119,8 @@ static void __init map_lowmem(void)
>
> create_mapping(&map);
> }
> +
> + memblock_set_current_limit(arm_lowmem_limit);
> }
>
> /*
> @@ -1123,8 +1131,6 @@ void __init paging_init(struct machine_desc *mdesc)
> {
> void *zero_page;
>
> - memblock_set_current_limit(arm_lowmem_limit);
> -
> build_mem_type_table();
> prepare_page_table();
> map_lowmem();
>
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org. For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: email@kvack.org
>

--
Kind regards,
Minchan Kim