Re: [PATCH -next v6 1/2] riscv: kdump: Implement crashkernel=X,[high,low]

chenjiahao (C)
2023-07-04T02:18:14Z

On 2023/7/2 12:12, Baoquan He wrote:
> On 07/01/23 at 05:11pm, Chen Jiahao wrote:
>> On riscv, the current crash kernel allocation logic is trying to
>> allocate within 32bit addressible memory region by default, if
>> failed, try to allocate without 4G restriction.
>>
>> In need of saving DMA zone memory while allocating a relatively large
>> crash kernel region, allocating the reserved memory top down in
>> high memory, without overlapping the DMA zone, is a mature solution.
>> Here introduce the parameter option crashkernel=X,[high,low].
>>
>> One can reserve the crash kernel from high memory above DMA zone range
>> by explicitly passing "crashkernel=X,high"; or reserve a memory range
>> below 4G with "crashkernel=X,low".
>>
>> Signed-off-by: Chen Jiahao <chenjiahao16@huawei.com>
>> Acked-by: Guo Ren <guoren@kernel.org>
>> ---
>> arch/riscv/kernel/setup.c | 5 +++
>> arch/riscv/mm/init.c | 84 +++++++++++++++++++++++++++++++++++----
>> 2 files changed, 82 insertions(+), 7 deletions(-)
>>
>> diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
>> index 971fe776e2f8..376f5d49ce85 100644
>> --- a/arch/riscv/kernel/setup.c
>> +++ b/arch/riscv/kernel/setup.c
>> @@ -178,6 +178,11 @@ static void __init init_resources(void)
>> if (ret < 0)
>> goto error;
>> }
>> + if (crashk_low_res.start != crashk_low_res.end) {
>> + ret = add_resource(&iomem_resource, &crashk_low_res);
>> + if (ret < 0)
>> + goto error;
>> + }
>> #endif
>>
>> #ifdef CONFIG_CRASH_DUMP
>> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
>> index 4b95d8999120..eeb31c2cc843 100644
>> --- a/arch/riscv/mm/init.c
>> +++ b/arch/riscv/mm/init.c
>> @@ -1298,6 +1298,28 @@ static inline void setup_vm_final(void)
>> }
>> #endif /* CONFIG_MMU */
>>
>> +/* Reserve 128M low memory by default for swiotlb buffer */
>> +#define DEFAULT_CRASH_KERNEL_LOW_SIZE (128UL << 20)
>> +
>> +static int __init reserve_crashkernel_low(unsigned long long low_size)
>> +{
>> + unsigned long long low_base;
>> +
>> + low_base = memblock_phys_alloc_range(low_size, PMD_SIZE, 0, dma32_phys_limit);
>> + if (!low_base) {
>> + pr_err("cannot allocate crashkernel low memory (size:0x%llx).\n", low_size);
>> + return -ENOMEM;
>> + }
>> +
>> + pr_info("crashkernel low memory reserved: 0x%016llx - 0x%016llx (%lld MB)\n",
>> + low_base, low_base + low_size, low_size >> 20);
>> +
>> + crashk_low_res.start = low_base;
>> + crashk_low_res.end = low_base + low_size - 1;
>> +
>> + return 0;
>> +}
>> +
>> /*
>> * reserve_crashkernel() - reserves memory for crash kernel
>> *
>> @@ -1309,8 +1331,12 @@ static void __init reserve_crashkernel(void)
>> {
>> unsigned long long crash_base = 0;
>> unsigned long long crash_size = 0;
>> + unsigned long long crash_low_size = 0;
>> unsigned long search_start = memblock_start_of_DRAM();
>> - unsigned long search_end = memblock_end_of_DRAM();
>> + unsigned long search_end = (unsigned long)dma32_phys_limit;
>> + char *cmdline = boot_command_line;
>> + bool fixed_base = false;
>> + bool high = false;
>>
>> int ret = 0;
>>
>> @@ -1326,14 +1352,36 @@ static void __init reserve_crashkernel(void)
>> return;
>> }
>>
>> - ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
>> + ret = parse_crashkernel(cmdline, memblock_phys_mem_size(),
>> &crash_size, &crash_base);
>> - if (ret || !crash_size)
>> + if (ret == -ENOENT) {
>> + /* Fallback to crashkernel=X,[high,low] */
>> + ret = parse_crashkernel_high(cmdline, 0, &crash_size, &crash_base);
>> + if (ret || !crash_size)
>> + return;
>> +
>> + /*
>> + * crashkernel=Y,low is valid only when crashkernel=X,high
>> + * is passed.
>> + */
>> + ret = parse_crashkernel_low(cmdline, 0, &crash_low_size, &crash_base);
>> + if (ret == -ENOENT)
>> + crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
>> + else if (ret)
>> + return;
>> +
>> + search_start = (unsigned long)dma32_phys_limit;
>> + search_end = memblock_end_of_DRAM();
>> + high = true;
>> + } else if (ret || !crash_size) {
>> + /* Invalid argument value specified */
>> return;
>> + }
>>
>> crash_size = PAGE_ALIGN(crash_size);
>>
>> if (crash_base) {
>> + fixed_base = true;
>> search_start = crash_base;
>> search_end = crash_base + crash_size;
>> }
>> @@ -1346,17 +1394,39 @@ static void __init reserve_crashkernel(void)
>> * swiotlb can work on the crash kernel.
>> */
>> crash_base = memblock_phys_alloc_range(crash_size, PMD_SIZE,
>> - search_start,
>> - min(search_end, (unsigned long) SZ_4G));
>> + search_start, search_end);
>> if (crash_base == 0) {
>> - /* Try again without restricting region to 32bit addressible memory */
>> + if (fixed_base) {
>> + pr_warn("crashkernel: allocating failed with given size@offset\n");
>> + return;
>> + }
>> +
>> + if (high) {
>> + /* Fall back to lower 32G reservation */
>> + search_start = memblock_start_of_DRAM();
>> + search_end = (unsigned long)dma32_phys_limit;
>> + } else {
>> + /* Try again above the region of 32bit addressible memory */
>> + search_start = (unsigned long)dma32_phys_limit;
>> + search_end = memblock_end_of_DRAM();
>> + }
>> +
>> crash_base = memblock_phys_alloc_range(crash_size, PMD_SIZE,
>> - search_start, search_end);
>> + search_start, search_end);
>> if (crash_base == 0) {
>> pr_warn("crashkernel: couldn't allocate %lldKB\n",
>> crash_size >> 10);
>> return;
>> }
>> +
>> + if (!crash_low_size)
>> + crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
> How do you differentiate the case user specifies crashkernel=0M,low
> explicitly with the case that user doesn't specify crashkernel=,low, but
> only specify crsahkernel=xM,high? I saw you don't have the test case
> crashkernel=xM,high crashkernel=0M,low listed in your cover letter.

Yes, here is indeed a point not exactly aligned with Arm64 code.
But testcases below seem to have the same result with Arm64:

crashkernel=512M,high //high=512M, low=128M (default)
crashkernel=512M,high crashkernel=0M,low //high=512M, low=0M
crashkernel=512M,high crashkernel=256M,low //high=512M, low=256M

When the first allocation succeed, it will not fallback into
the if (crash_base == 0) case, the allocation result is the same
as Arm64, both for explicitly given "crashkernel=0M,low" or not.

The problem you mentioned might occurs when the first allocation
failed.

My logic here is when crashkernel=xM,high is specified, no matter
crashkernel=0M,low is explicitly given or not, "high" flag is set.
It will fallback to lower 4G allocation, additional lower 4G region
with "crash_low_size" will never get reserved.

So the results between Arm64 and riscv when crashkernel=,low is
specified or not are the same. Is there any problem with my logic,
or have I misunderstood your comment above?

>
>> + }
>> +
>> + if ((crash_base >= dma32_phys_limit) && crash_low_size &&
>> + reserve_crashkernel_low(crash_low_size)) {

Here, additional lower memory region will not reserve when
crashkernel=xM,high is given

>> + memblock_phys_free(crash_base, crash_size);
>> + return;
>> }
>>
>> pr_info("crashkernel: reserved 0x%016llx - 0x%016llx (%lld MB)\n",
>> --
>> 2.34.1
>>
Thanks,

Jiahao