Re: [PATCH v20 3/5] arm64: kdump: reimplement crashkernel=X

From: Leizhen (ThunderTown)
Date: Mon Feb 14 2022 - 01:44:22 EST



On 2022/2/11 18:51, Baoquan He wrote:
> On 02/11/22 at 06:41pm, Leizhen (ThunderTown) wrote:
>>
>>
>> On 2022/2/11 18:30, Baoquan He wrote:
>>> On 01/24/22 at 04:47pm, Zhen Lei wrote:
>>>> From: Chen Zhou <chenzhou10@xxxxxxxxxx>
>>> ......
>>>> 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
>>>> *
>>>> @@ -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;
>>>
>>> Here, the error case is not checked and handled. But it still gets
>>> expeced result which is the default SZ_256M. Is this designed on
>>> purpose?
>>
>> Yes, we can specify only "crashkernel=X,high".
>>
>> This is mentioned in Documentation/admin-guide/kernel-parameters.txt
>>
>> crashkernel=size[KMG],low
>> [KNL, X86-64] range under 4G. When crashkernel=X,high
>> is passed, kernel could allocate physical memory region
>> above 4G, that cause second kernel crash on system
>> that require some amount of low memory, e.g. swiotlb
>> requires at least 64M+32K low memory, also enough extra
>> low memory is needed to make sure DMA buffers for 32-bit
>> devices won't run out. Kernel would try to allocate at <---------
>> least 256M below 4G automatically. <---------
>
> Yeah, that is expected becasue no crahskernel=,low is a right usage. The
> 'ret' is 0 in the case. If I gave below string, it works too.
> "crashkernel=256M,high crashkernel=aaabbadfadfd,low"

Yes, so maybe we should change the error code in __parse_crashkernel()
from "-EINVAL" to "-ENOENT" when the specified option does not exist.

diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 256cf6db573cd09..395f4fac1773f28 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -243,9 +243,8 @@ static int __init __parse_crashkernel(char *cmdline,
*crash_base = 0;

ck_cmdline = get_last_crashkernel(cmdline, name, suffix);
-
if (!ck_cmdline)
- return -EINVAL;
+ return -ENOENT;

ck_cmdline += strlen(name);


>
>>
>>>
>>>> +
>>>> + 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
>>
>
> .
>

--
Regards,
Zhen Lei