Re: [PATCH v23 3/6] arm64: kdump: Reimplement crashkernel=X

Catalin Marinas
2022-05-05T17:02:05Z

On Thu, May 05, 2022 at 05:18:42PM +0800, Zhen Lei wrote:
> From: Chen Zhou <chenzhou10@huawei.com>
>
> There are following issues in arm64 kdump:
> 1. We use crashkernel=X to reserve crashkernel in DMA zone, which
> will fail when there is not enough low memory.
> 2. If reserving crashkernel above DMA zone, in this case, crash dump
> kernel will fail to boot because there is no low memory available
> for allocation.
>
> To solve these issues, introduce crashkernel=X,[high,low].
> The "crashkernel=X,high" is used to select a region above DMA zone, and
> the "crashkernel=Y,low" is used to allocate specified size low memory.

Thanks for posting the simplified version, though the discussion with
Baoquan is still ongoing. AFAICT there is no fallback if crashkernel=
fails. The advantage with this series is cleaner code, we set the limits
during parsing and don't have to adjust them if some of the first
allocation failed.

> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 51863f1448c6989..11406f3e1443168 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -90,6 +90,32 @@ phys_addr_t __ro_after_init arm64_dma_phys_limit;
> phys_addr_t __ro_after_init arm64_dma_phys_limit = PHYS_MASK + 1;
> #endif
>
> +/* 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

Better use memblock_get_current_limit() if you need to or just
MEMBLOCK_ALLOC_ANYWHERE, memblock.current_limit is just a memblock
internal. But I think we can go for (PHYS_MASK + 1) if you need
something other than MEMBLOCK_ALLOC_ANYWHERE, memblock knows what to
allocate anyway.

> +static int __init reserve_crashkernel_low(unsigned long long low_size)
> +{
> + unsigned long long low_base;
> +
> + 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
> *
> @@ -100,17 +126,32 @@ phys_addr_t __ro_after_init arm64_dma_phys_limit = PHYS_MASK + 1;
> 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 = 0;
> + unsigned long long crash_max = CRASH_ADDR_LOW_MAX;
> + char *cmdline = boot_command_line;
> int ret;
>
> if (!IS_ENABLED(CONFIG_KEXEC_CORE))
> return;
>
> - 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) {

I think we should check for ret == -ENOENT only. If the crashkernel=
exists but is malformed or the size is 0, we shouldn't bother with
high/low at all.

> + ret = parse_crashkernel_high(cmdline, 0, &crash_size, &crash_base);
> + if (ret || !crash_size)
> + return;
> +
> + /*
> + * crashkernel=Y,low can be specified or not, but invalid value
> + * is not allowed.
> + */
> + ret = parse_crashkernel_low(cmdline, 0, &crash_low_size, &crash_base);
> + if (ret && (ret != -ENOENT))
> + return;
> +
> + crash_max = CRASH_ADDR_HIGH_MAX;
> + }
>
> crash_size = PAGE_ALIGN(crash_size);
>
> @@ -118,8 +159,7 @@ static void __init reserve_crashkernel(void)
> if (crash_base)
> crash_max = crash_base + crash_size;
>
> - /* Current arm64 boot protocol requires 2MB alignment */
> - crash_base = memblock_phys_alloc_range(crash_size, SZ_2M,
> + crash_base = memblock_phys_alloc_range(crash_size, CRASH_ALIGN,
> crash_base, crash_max);
> if (!crash_base) {
> pr_warn("cannot allocate crashkernel (size:0x%llx)\n",

I personally like this but let's see how the other thread goes. I guess
if we want a fallback, it would come just before the check the above:

if (!crash_base && crash_max != CRASH_ADDR_HIGH_MAX) {
/* attempt high allocation with default low */
if (!crash_low_size)
crash_low_size = some default;
crash_max = CRASH_ADDR_LOW_MAX;
crash_base = memblock_phys_alloc_range();
}

Well, I guess we end up with your earlier proposal but I think I
understand it better now ;).

--
Catalin