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

Baoquan He
2022-03-16T12:12:09Z

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.

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
>