Re: [PATCH v24 3/6] arm64: kdump: Reimplement crashkernel=X

Leizhen (ThunderTown)
2022-05-07T12:20:58Z

On 2022/5/7 19:49, Leizhen (ThunderTown) wrote:
>
>
> On 2022/5/7 17:35, Leizhen (ThunderTown) wrote:
>>
>>
>> On 2022/5/7 11:37, Leizhen (ThunderTown) wrote:
>>>
>>>
>>> On 2022/5/7 10:07, Baoquan He wrote:
>>>> On 05/07/22 at 09:34am, Leizhen (ThunderTown) wrote:
>>>>>
>>>>>
>>>>> On 2022/5/7 7:10, Baoquan He wrote:
>>>>>> On 05/06/22 at 07:43pm, Zhen Lei wrote:
>>>>>> ......
>>>>>>> @@ -118,8 +162,7 @@ static void __init reserve_crashkernel(void)
>>>>>>> if (crash_base)
>>>>>>> crash_max = crash_base + crash_size;
>>>>>>>
>>>>>>> - /* Current arm64 boot protocol requires 2MB alignment */
>>>>>>> - crash_base = memblock_phys_alloc_range(crash_size, SZ_2M,
>>>>>>> + crash_base = memblock_phys_alloc_range(crash_size, CRASH_ALIGN,
>>>>>>> crash_base, crash_max);
>>>>>>> if (!crash_base) {
>>>>>>> pr_warn("cannot allocate crashkernel (size:0x%llx)\n",
>>>>>>> @@ -127,6 +170,11 @@ static void __init reserve_crashkernel(void)
>>>>>>> return;
>>>>>>> }
>>>>>>>
>>>>>>
>>>>>> There's corner case missed, e.g
>>>>>> 1) ,high and ,low are specified, CONFIG_ZONE_DMA|DMA32 is not enabled;
>>>>>> 2) ,high and ,low are specified, the whole system memory is under 4G.
>>>>>>
>>>>>> Below judgement can filter them away:
>>>>>>
>>>>>> if (crash_base > arm64_dma_phys_limit && crash_low_size &&
>>>>>> reserve_crashkernel_low(crash_low_size)) {
>>>>>>
>>>>>> What's your opinion? Leave it and add document to notice user, or fix it
>>>>>> with code change?

I've now got the patch ready as suggested, to be as consistent as possible
with x86.

Just wait for next Monday Catalin's response: a seperate patch or v25?

>>
>> I decided to modify the code and document. But the code changes aren't what
>> you suggested. For the following reasons:
>> 1. The memory allocated for 'high' may be partially under 4G. So the low
>> memory may not be enough. Of course, it's rare.
>> 2. The second kernel can work properly only when the high and low memory
>> are successfully applied for. For example, high=128M, low=128M, but the
>> second kernel need 256M.
>>
>> So for the cases you listed:
>> 1) ,high and ,low are specified, CONFIG_ZONE_DMA|DMA32 is not enabled;
>> --> Follow you suggestion, ignore crashkernel=Y,low, don't allocate low memory.
>>
>> @@ -100,6 +100,14 @@ static int __init reserve_crashkernel_low(unsigned long long low_size)
>> {
>> unsigned long long low_base;
>>
>> + /*
>> + * The kernel does not have any DMA zone, so the range of each DMA
>> + * zone is unknown. Please make sure both CONFIG_ZONE_DMA and
>> + * CONFIG_ZONE_DMA32 are also not set in the second kernel.
>> + */
>> + if (!IS_ENABLED(CONFIG_ZONE_DMA) && !IS_ENABLED(CONFIG_ZONE_DMA32))
>> + return 0;
>> +
>>
>> 2) ,high and ,low are specified, the whole system memory is under 4G.
>> --> two memory ranges will be allocated, the size is what 'high' and 'low' specified.
>> --> Yes, the memory of 'low' may be above 'high', but the 'high' just hint allocation
>> --> from top, try high memory first. Of course, this may cause kexec to fail to load.
>> --> Because the memory of 'low' with small size will be used to store Image, etc..
>> --> But the memory of 'low' above 'high' is almost impossible, we use memblock API to
>> --> allocate memory from top to bottem, 'low' above 'high' need a sizeable memory block
>> --> (128M, 256M?) to be freed at init phase.
>> --> Maybe I should add: crash_max = min(crash_base, CRASH_ADDR_LOW_MAX);
>> --> to make sure the memory of 'low' is always under 'high'
>
> I have added the min() above.
>
> Test result:
> 1) ,high and ,low are specified, CONFIG_ZONE_DMA|DMA32 is not enabled;
> root@localhost:~# dmesg | grep crash
> [ 0.000000] crashkernel reserved: 0x0000000420000000 - 0x0000000440000000 (512 MB)
> [ 0.000000] Kernel command line: console=ttyAMA0 root=/dev/vda rw panic_on_oops=1 oops=panic crashkernel=512M,high crashkernel=128M,low
>
> 2) ,high and ,low are specified, the whole system memory is under 4G.
> root@localhost:~# dmesg | grep crash
> [ 0.000000] crashkernel tmp reserved: 0x00000000f2800000 - 0x00000000fa800000 (128 MB)
> [ 0.000000] crashkernel low memory reserved: 0xca800000 - 0xd2800000 (128 MB)
> [ 0.000000] crashkernel reserved: 0x00000000d2800000 - 0x00000000f2800000 (512 MB)
> [ 0.000000] Kernel command line: console=ttyAMA0 root=/dev/vda rw panic_on_oops=1 oops=panic crashkernel=512M,high crashkernel=128M,low
>
> test stub for 2):
>
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 5cb73bbd286b100..abbde2158a0976a 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -147,6 +147,7 @@ static void __init reserve_crashkernel(void)
> unsigned long long crash_max = CRASH_ADDR_LOW_MAX;
> char *cmdline = boot_command_line;
> int ret;
> + unsigned long long tmp_base;
>
> if (!IS_ENABLED(CONFIG_KEXEC_CORE))
> return;
> @@ -179,6 +180,11 @@ static void __init reserve_crashkernel(void)
> if (crash_base)
> crash_max = crash_base + crash_size;
>
> + tmp_base = memblock_phys_alloc_range(crash_low_size, CRASH_ALIGN, crash_base, crash_max);
> + BUG_ON(!tmp_base);
> + pr_info("crashkernel tmp reserved: 0x%016llx - 0x%016llx (%lld MB)\n",
> + tmp_base, tmp_base + crash_low_size, crash_low_size >> 20);
> +
> crash_base = memblock_phys_alloc_range(crash_size, CRASH_ALIGN,
> crash_base, crash_max);
> if (!crash_base) {
> @@ -186,6 +192,7 @@ static void __init reserve_crashkernel(void)
> crash_size);
> return;
> }
> + memblock_phys_free(tmp_base, crash_low_size);
>
> if (crash_low_size && reserve_crashkernel_low(crash_low_size, crash_base)) {
> memblock_phys_free(crash_base, crash_size);
>
>>
>>>>>
>>>>> I think maybe we can leave it unchanged. If the user configures two memory ranges,
>>>>> we'd better apply for two. Otherwise, he'll be confused when he inquires. Currently,
>>>>> crash_low_size is non-zero only when 'crashkernel=Y,low' is explicitly configured.
>>>>
>>>> Then user need know the system information, e.g how much is the high
>>>> memory, low memory, if CONFIG_ZONE_DMA|DMA32 is enabled. And we need
>>>> describe these cases in document. Any corner case or exception need
>>>> be noted if we don't handle it in code.
>>>>
>>>> Caring about this very much because we have CI with existed test cases
>>>> to run on the system, and QA will check these manually too. Support
>>>> engineer need detailed document if anything special but happened.
>>>> Anything unclear or uncovered will be reported as bug to our kernel dev.
>>>> Guess your company do the similar thing like this.
>>>>
>>>> This crashkerne,high and crashkernel,low reservation is special if we
>>>> allow ,high, ,low existing in the same zone. Imagine on system with
>>>> CONFIG_ZONE_DMA|DMA32 disabled, people copy the crashkernel=512M,high
>>>> and crashkernel=128M,low from other system, and he could get
>>>> crash_res at [5G, 5G+512M], while crash_low_res at [6G, 6G+128M]. Guess
>>>> how they will judge us.
>>>
>>> OK, I got it.
>>>
>>>>
>>>>>
>>>>>>
>>>>>> I would suggest merging this series, Lei can add this corner case
>>>>>> handling on top. Since this is a newly added support, we don't have
>>>>>> to make it one step. Doing step by step can make reviewing easier.
>>>>>>
>>>>>>> + if (crash_low_size && reserve_crashkernel_low(crash_low_size)) {
>>>>>>> + memblock_phys_free(crash_base, crash_size);
>>>>>>> + return;
>>>>>>> + }
>>>>>>> +
>>>>>>> pr_info("crashkernel reserved: 0x%016llx - 0x%016llx (%lld MB)\n",
>>>>>>> crash_base, crash_base + crash_size, crash_size >> 20);
>>>>>>>
>>>>>>> @@ -135,6 +183,9 @@ static void __init reserve_crashkernel(void)
>>>>>>> * map. Inform kmemleak so that it won't try to access it.
>>>>>>> */
>>>>>>> kmemleak_ignore_phys(crash_base);
>>>>>>> + if (crashk_low_res.end)
>>>>>>> + kmemleak_ignore_phys(crashk_low_res.start);
>>>>>>> +
>>>>>>> crashk_res.start = crash_base;
>>>>>>> crashk_res.end = crash_base + crash_size - 1;
>>>>>>> insert_resource(&iomem_resource, &crashk_res);
>>>>>>> --
>>>>>>> 2.25.1
>>>>>>>
>>>>>>
>>>>>> .
>>>>>>
>>>>>
>>>>> --
>>>>> Regards,
>>>>> Zhen Lei
>>>>>
>>>>
>>>> .
>>>>
>>>
>>
>

--
Regards,
Zhen Lei