Re: [PATCH v21 3/5] arm64: kdump: reimplement crashkernel=X

["Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>]

On 2022/3/21 21:29, John Donnelly wrote:
> On 2/26/22 9:07 PM, Zhen Lei wrote:
>> From: Chen Zhou <chenzhou10@huawei.com>
>>
>> There are following issues in arm64 kdump:
>> 1. We use crashkernel=X to reserve crashkernel below 4G, which
>> will fail when there is no enough low memory.
> 
>                         " Not enough "

OK, thanks

>> 2. If reserving crashkernel above 4G, in this case, crash dump
>> kernel will boot failure because there is no low memory available
>> for allocation.
> 
>  We can't have a "boot failure". If the requested reservation
>  can not be met,  the kdump  configuration is not setup.
>>
>> To solve these issues, change the behavior of crashkernel=X and
>> introduce crashkernel=X,[high,low]. crashkernel=X tries low allocation
>> in DMA zone, and fall back to high allocation if it fails.
>> We can also use "crashkernel=X,high" to select a region above DMA zone,
>> which also tries to allocate at least 256M in DMA zone automatically.
>> "crashkernel=Y,low" can be used to allocate specified size low memory.
> 
> Is there going to be documentation on what values certain Arm platforms are going to use this on ?

There is no exact formula.

> 
>>
>> Signed-off-by: Chen Zhou <chenzhou10@huawei.com>
>> Co-developed-by: Zhen Lei <thunder.leizhen@huawei.com>
>> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
>> ---
>>   arch/arm64/kernel/machine_kexec.c      |   9 ++-
>>   arch/arm64/kernel/machine_kexec_file.c |  12 ++-
>>   arch/arm64/mm/init.c                   | 106 +++++++++++++++++++++++--
>>   3 files changed, 115 insertions(+), 12 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
>> index e16b248699d5c3c..19c2d487cb08feb 100644
>> --- a/arch/arm64/kernel/machine_kexec.c
>> +++ b/arch/arm64/kernel/machine_kexec.c
>> @@ -329,8 +329,13 @@ bool crash_is_nosave(unsigned long pfn)
>>         /* in reserved memory? */
>>       addr = __pfn_to_phys(pfn);
>> -    if ((addr < crashk_res.start) || (crashk_res.end < addr))
>> -        return false;
>> +    if ((addr < crashk_res.start) || (crashk_res.end < addr)) {
>> +        if (!crashk_low_res.end)
>> +            return false;
>> +
>> +        if ((addr < crashk_low_res.start) || (crashk_low_res.end < addr))
>> +            return false;
>> +    }
>>         if (!kexec_crash_image)
>>           return true;
>> diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c
>> index 59c648d51848886..889951291cc0f9c 100644
>> --- a/arch/arm64/kernel/machine_kexec_file.c
>> +++ b/arch/arm64/kernel/machine_kexec_file.c
>> @@ -65,10 +65,18 @@ static int prepare_elf_headers(void **addr, unsigned long *sz)
>>         /* Exclude crashkernel region */
>>       ret = crash_exclude_mem_range(cmem, crashk_res.start, crashk_res.end);
>> +    if (ret)
>> +        goto out;
>> +
>> +    if (crashk_low_res.end) {
>> +        ret = crash_exclude_mem_range(cmem, crashk_low_res.start, crashk_low_res.end);
>> +        if (ret)
>> +            goto out;
>> +    }
>>   -    if (!ret)
>> -        ret =  crash_prepare_elf64_headers(cmem, true, addr, sz);
>> +    ret = crash_prepare_elf64_headers(cmem, true, addr, sz);
>>   +out:
>>       kfree(cmem);
>>       return ret;
>>   }
>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>> index 90f276d46b93bc6..30ae6638ff54c47 100644
>> --- a/arch/arm64/mm/init.c
>> +++ b/arch/arm64/mm/init.c
>> @@ -65,6 +65,44 @@ EXPORT_SYMBOL(memstart_addr);
>>   phys_addr_t arm64_dma_phys_limit __ro_after_init;
>>     #ifdef CONFIG_KEXEC_CORE
>> +/* Current arm64 boot protocol requires 2MB alignment */
>> +#define CRASH_ALIGN            SZ_2M
>> +
>> +#define CRASH_ADDR_LOW_MAX        arm64_dma_phys_limit
>> +#define CRASH_ADDR_HIGH_MAX        memblock.current_limit
>> +
>> +/*
>> + * This is an empirical value in x86_64 and taken here directly. Please
>> + * refer to the code comment in reserve_crashkernel_low() of x86_64 for more
>> + * details.
>> + */
>> +#define DEFAULT_CRASH_KERNEL_LOW_SIZE    \
>> +    max(swiotlb_size_or_default() + (8UL << 20), 256UL << 20)
>> +
>> +static int __init reserve_crashkernel_low(unsigned long long low_size)
>> +{
>> +    unsigned long long low_base;
>> +
>> +    /* passed with crashkernel=0,low ? */
>> +    if (!low_size)
>> +        return 0;
>> +
>> +    low_base = memblock_phys_alloc_range(low_size, CRASH_ALIGN, 0, CRASH_ADDR_LOW_MAX);
>> +    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%08llx - 0x%08llx (%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;
>> +    insert_resource(&iomem_resource, &crashk_low_res);
>> +
>> +    return 0;
>> +}
>> +
>>   /*
>>    * reserve_crashkernel() - reserves memory for crash kernel
>>    *
>> @@ -75,30 +113,79 @@ phys_addr_t arm64_dma_phys_limit __ro_after_init;
>>   static void __init reserve_crashkernel(void)
>>   {
>>       unsigned long long crash_base, crash_size;
>> -    unsigned long long crash_max = arm64_dma_phys_limit;
>> +    unsigned long long crash_low_size;
>> +    unsigned long long crash_max = CRASH_ADDR_LOW_MAX;
>>       int ret;
>> +    bool fixed_base, high = false;
>> +    char *cmdline = boot_command_line;
>>   -    ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
>> +    /* crashkernel=X[@offset] */
>> +    ret = parse_crashkernel(cmdline, memblock_phys_mem_size(),
>>                   &crash_size, &crash_base);
>> -    /* no crashkernel= or invalid value specified */
>> -    if (ret || !crash_size)
>> -        return;
>> +    if (ret || !crash_size) {
>> +        /* crashkernel=X,high */
>> +        ret = parse_crashkernel_high(cmdline, 0, &crash_size, &crash_base);
>> +        if (ret || !crash_size)
>> +            return;
>> +
>> +        /* crashkernel=Y,low */
>> +        ret = parse_crashkernel_low(cmdline, 0, &crash_low_size, &crash_base);
>> +        if (ret == -ENOENT)
>> +            /*
>> +             * crashkernel=Y,low is not specified explicitly, use
>> +             * default size automatically.
>> +             */
>> +            crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
>> +        else if (ret)
>> +            /* crashkernel=Y,low is specified but Y is invalid */
>> +            return;
>> +
>> +        /* Mark crashkernel=X,high is specified */
>> +        high = true;
>> +        crash_max = CRASH_ADDR_HIGH_MAX;
>> +    }
>>   +    fixed_base = !!crash_base;
>>       crash_size = PAGE_ALIGN(crash_size);
>>         /* User specifies base address explicitly. */
>> -    if (crash_base)
>> +    if (fixed_base)
>>           crash_max = crash_base + crash_size;
>>   -    /* Current arm64 boot protocol requires 2MB alignment */
>> -    crash_base = memblock_phys_alloc_range(crash_size, SZ_2M,
>> +retry:
>> +    crash_base = memblock_phys_alloc_range(crash_size, CRASH_ALIGN,
>>                              crash_base, crash_max);
>>       if (!crash_base) {
>> +        /*
>> +         * Attempt to fully allocate low memory failed, fall back
>> +         * to high memory, the minimum required low memory will be
>> +         * reserved later.
>> +         */
>> +        if (!fixed_base && (crash_max == CRASH_ADDR_LOW_MAX)) {
>> +            crash_max = CRASH_ADDR_HIGH_MAX;
>> +            goto retry;
>> +        }
>> +
>>           pr_warn("cannot allocate crashkernel (size:0x%llx)\n",
>>               crash_size);
>>           return;
>>       }
>>   +    if (crash_base >= SZ_4G) {
>> +        /*
>> +         * For case crashkernel=X, low memory is not enough and fall
>> +         * back to reserve specified size of memory above 4G, try to
>> +         * allocate minimum required memory below 4G again.
>> +         */
>> +        if (!high)
>> +            crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
>> +
>> +        if (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);
>>   @@ -107,6 +194,9 @@ 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);
> 
> .
> 

-- 
Regards,
  Zhen Lei