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

Leizhen (ThunderTown)
2022-03-16T13:12:14Z

On 2022/3/16 20:11, Baoquan He wrote:
> On 02/27/22 at 11:07am, 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.
>> 2. If reserving crashkernel above 4G, in this case, crash dump
>> kernel will boot failure because there is no low memory available
>> for allocation.
>>
>> 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.
>>
>> 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;
>
> Even though reverse xmas tree style is not enforced, this 'int ret;' is
> really annoying to look at. Maybe move it down two lines.
>
>> + 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. */
> This is over commenting, can't see why it's needed.
>> - if (crash_base)
>> + if (fixed_base)
>> crash_max = crash_base + crash_size;
>
> Hi leizhen,
>
> I made change on reserve_crashkenrel(), inline comment may be slow.
> Please check and consider if they can be taken.

That's great. Thank you very much.

>
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 30ae6638ff54..f96351da1e3e 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -109,38 +109,43 @@ static int __init reserve_crashkernel_low(unsigned long long low_size)
> * This function reserves memory area given in "crashkernel=" kernel command
> * line parameter. The memory reserved is used by dump capture kernel when
> * primary kernel is crashing.
> + *
> + * NOTE: Reservation of crashkernel,low is special since its existence
> + * is not independent, need rely on the existence of crashkernel,high.
> + * Hence there are different cases for crashkernel,low reservation:
> + * 1) crashkernel=Y,low is specified explicitly, crashkernel,low takes Y;
> + * 2) crashkernel=,low is not given, while crashkernel=,high is specified,
> + * take the default crashkernel,low value;
> + * 3) crashkernel=X is specified, while fallback to get a memory region
> + * in high memory, take the default crashkernel,low value;
> + * 4) crashkernel='invalid value',low is specified, failed the whole
> + * crashkernel reservation and bail out.
> */
> static void __init reserve_crashkernel(void)
> {
> unsigned long long crash_base, crash_size;
> 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;
> + int ret;
>
> /* crashkernel=X[@offset] */
> ret = parse_crashkernel(cmdline, memblock_phys_mem_size(),
> &crash_size, &crash_base);
> 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.
> - */
> + /* case #2 of crashkernel,low reservation */
> crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
> else if (ret)
> - /* crashkernel=Y,low is specified but Y is invalid */
> + /* case #4 of crashkernel,low reservation */
> return;
>
> - /* Mark crashkernel=X,high is specified */
> high = true;
> crash_max = CRASH_ADDR_HIGH_MAX;
> }
> @@ -148,7 +153,6 @@ static void __init reserve_crashkernel(void)
> fixed_base = !!crash_base;
> crash_size = PAGE_ALIGN(crash_size);
>
> - /* User specifies base address explicitly. */
> if (fixed_base)
> crash_max = crash_base + crash_size;
>
> @@ -172,11 +176,7 @@ static void __init reserve_crashkernel(void)
> }
>
> 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.
> - */
> + /* case #3 of crashkernel,low reservation */
> if (!high)
> crash_low_size = DEFAULT_CRASH_KERNEL_LOW_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);
>> --
>> 2.25.1
>>
>
> .
>

--
Regards,
Zhen Lei