[PATCH v20 3/5] arm64: kdump: reimplement crashkernel=X
Leizhen (ThunderTown)
thunder.leizhen at huawei.com
Tue Feb 15 18:58:31 PST 2022
On 2022/2/14 15:53, Leizhen (ThunderTown) wrote:
>
>
> On 2022/2/14 11:52, Baoquan He wrote:
>> On 01/24/22 at 04:47pm, Zhen Lei wrote:
>> ......
>>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>>> index 6c653a2c7cff052..a5d43feac0d7d96 100644
>>> --- a/arch/arm64/mm/init.c
>>> +++ b/arch/arm64/mm/init.c
>>> @@ -71,6 +71,30 @@ phys_addr_t arm64_dma_phys_limit __ro_after_init;
>>> #define CRASH_ADDR_LOW_MAX arm64_dma_phys_limit
>>> #define CRASH_ADDR_HIGH_MAX MEMBLOCK_ALLOC_ACCESSIBLE
>>>
>>> +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%llx - 0x%llx (%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
>>
>> My another concern is the crashkernel=,low handling. In this patch, the
>> code related to low memory is obscure. Wondering if we should make them
>> explicit with a little redundant but very clear code flows. Saying this
>> because the code must be very clear to you and reviewers, it may be
>> harder for later code reader or anyone interested to understand.
>>
>> 1) crashkernel=X,high
>> 2) crashkernel=X,high crashkernel=Y,low
>> 3) crashkernel=X,high crashkernel=0,low
>> 4) crashkernel=X,high crashkernel='messy code',low
>> 5) crashkernel=X //fall back to high memory, low memory is required then.
>>
>> It could be me thinking about it too much. I made changes to your patch
>> with a tuning, not sure if it's OK to you. Otherwise, this patchset
>
> I think it's good.
>
>> works very well for all above test cases, it's ripe to be merged for
>> wider testing.
>
> I will test it tomorrow. I've prepared a little more use cases than yours.
After the following modifications, I have tested it and it works well. Passed
all the test cases I prepared.
>
> 1) crashkernel=4G //high=4G, low=256M
> 2) crashkernel=4G crashkernel=512M,high crashkernel=512M,low //high=4G, low=256M, high and low are ignored
> 3) crashkernel=4G crashkernel=512M,high //high=4G, low=256M, high is ignored
> 4) crashkernel=4G crashkernel=512M,low //high=4G, low=256M, low is ignored
> 5) crashkernel=4G at 0xe0000000 //high=0G, low=0M, cannot allocate, failed
> 6) crashkernel=512M //high=0G, low=512M
> 7) crashkernel=128M //high=0G, low=128M
> 8) crashkernel=512M at 0xde000000 //512M at 3552M //high=0G, low=512M
> 9) crashkernel=4G,high //high=4G, low=256M
> a) crashkernel=4G,high crashkernel=512M,low //high=4G, low=512M
> b) crashkernel=512M,high crashkernel=128M,low //high=512M, low=128M
> c) crashkernel=512M,low //high=0G, low=0M, invalid
>
>
>>
>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>> index a5d43feac0d7..671862c56d7d 100644
>> --- a/arch/arm64/mm/init.c
>> +++ b/arch/arm64/mm/init.c
>> @@ -94,7 +94,8 @@ static int __init reserve_crashkernel_low(unsigned long long low_size)
>>
>> return 0;
>> }
>> -
>> +/*Words explaining why it's 256M*/
>> +#define DEFAULT_CRASH_KERNEL_LOW_SIZE SZ_256M
It's an empirical value.
94fb9334182284e8e7e4bcb9125c25dc33af19d4 x86/crash: Allocate enough low memory when crashkernel=high
When the crash kernel is loaded above 4GiB in memory, the
first kernel allocates only 72MiB of low-memory for the DMA
requirements of the second kernel. On systems with many
devices this is not enough and causes device driver
initialization errors and failed crash dumps. Testing by
SUSE and Redhat has shown that 256MiB is a good default
value for now and the discussion has lead to this value as
well. So set this default value to 256MiB to make sure there
is enough memory available for DMA.
>> /*
>> * reserve_crashkernel() - reserves memory for crash kernel
>> *
>> @@ -105,10 +106,10 @@ static int __init reserve_crashkernel_low(unsigned long long low_size)
>> static void __init reserve_crashkernel(void)
>> {
>> unsigned long long crash_base, crash_size;
>> - unsigned long long crash_low_size = SZ_256M;
>> + unsigned long long crash_low_size;
>> unsigned long long crash_max = CRASH_ADDR_LOW_MAX;
>> int ret;
>> - bool fixed_base;
>> + bool fixed_base, high;
high = false;
>> char *cmdline = boot_command_line;
>>
>> /* crashkernel=X[@offset] */
>> @@ -126,7 +127,10 @@ static void __init reserve_crashkernel(void)
>> ret = parse_crashkernel_low(cmdline, 0, &low_size, &crash_base);
>> if (!ret)
>> crash_low_size = low_size;
>> + else
>> + crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
>>
>> + high = true;
>> crash_max = CRASH_ADDR_HIGH_MAX;
>> }
>>
>> @@ -134,7 +138,7 @@ static void __init reserve_crashkernel(void)
>> crash_size = PAGE_ALIGN(crash_size);
>>
>> /* User specifies base address explicitly. */
>> - if (crash_base)
>> + if (fixed_base)
>> crash_max = crash_base + crash_size;
>>
>> retry:
>> @@ -156,7 +160,10 @@ static void __init reserve_crashkernel(void)
>> return;
>> }
>>
>> - if (crash_base >= SZ_4G && reserve_crashkernel_low(crash_low_size)) {
>> + if (crash_base >= SZ_4G && !high)
>> + crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
>> +
>> + if (reserve_crashkernel_low(crash_low_size)) {
>> memblock_phys_free(crash_base, crash_size);
>> return;
>> }
- if (crash_base >= SZ_4G && reserve_crashkernel_low(crash_low_size)) {
- memblock_phys_free(crash_base, crash_size);
- return;
+ if (crash_base >= SZ_4G) {
+ if (!high)
+ crash_low_size = SZ_256M;
+
+ if (reserve_crashkernel_low(crash_low_size)) {
+ memblock_phys_free(crash_base, crash_size);
+ return;
+ }
}
Looks like changing 'high' to 'low' would be more accurate. Whether crashkernel=Y,low is specified.
>
> It feels like {} may need to be added here so that it is in branch "if (crash_base >= SZ_4G)".
> The case of "crashkernel=128M" will not fall back to high memory and does not need to reserve
> low memory again.
>
>>
>>> *
>>> @@ -81,29 +105,62 @@ 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_low_size = SZ_256M;
>>> unsigned long long crash_max = CRASH_ADDR_LOW_MAX;
>>> int ret;
>>> + bool fixed_base;
>>> + 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) {
>>> + unsigned long long low_size;
>>>
>>> + /* crashkernel=X,high */
>>> + ret = parse_crashkernel_high(cmdline, 0, &crash_size, &crash_base);
>>> + if (ret || !crash_size)
>>> + return;
>>> +
>>> + /* crashkernel=X,low */
>>> + ret = parse_crashkernel_low(cmdline, 0, &low_size, &crash_base);
>>> + if (!ret)
>>> + crash_low_size = low_size;
>>> +
>>> + crash_max = CRASH_ADDR_HIGH_MAX;
>>> + }
>>> +
>>> + fixed_base = !!crash_base;
>>> crash_size = PAGE_ALIGN(crash_size);
>>>
>>> /* User specifies base address explicitly. */
>>> if (crash_base)
>>> crash_max = crash_base + crash_size;
>>>
>>> +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 && 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);
>>>
>>> @@ -112,6 +169,9 @@ 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
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