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SubjectRe: [PATCH 1/4] x86: kdump: move reserve_crashkernel_low() into kexec_core.c
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Hello,

On 07/05/2019 04:50, Chen Zhou wrote:
> In preparation for supporting reserving crashkernel above 4G
> in arm64 as x86_64 does, move reserve_crashkernel_low() into
> kexec/kexec_core.c.


> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index 905dae8..9ee33b6 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -463,59 +460,6 @@ static void __init memblock_x86_reserve_range_setup_data(void)
> # define CRASH_ADDR_HIGH_MAX MAXMEM
> #endif
>
> -static int __init reserve_crashkernel_low(void)
> -{
> -#ifdef CONFIG_X86_64

The behaviour of this #ifdef has disappeared, won't 32bit x86 now try and reserve a chunk
of unnecessary 'low' memory?

[...]


> @@ -579,9 +523,13 @@ static void __init reserve_crashkernel(void)
> return;
> }
>
> - if (crash_base >= (1ULL << 32) && reserve_crashkernel_low()) {
> - memblock_free(crash_base, crash_size);
> - return;
> + if (crash_base >= (1ULL << 32)) {
> + if (reserve_crashkernel_low()) {
> + memblock_free(crash_base, crash_size);
> + return;
> + }
> +
> + insert_resource(&iomem_resource, &crashk_low_res);


Previously reserve_crashkernel_low() was #ifdefed to do nothing if !CONFIG_X86_64, I don't
see how 32bit is skipping this reservation...


> }
>
> pr_info("Reserving %ldMB of memory at %ldMB for crashkernel (System RAM: %ldMB)\n",
> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> index b9b1bc5..096ad63 100644
> --- a/include/linux/kexec.h
> +++ b/include/linux/kexec.h
> @@ -63,6 +63,10 @@
>
> #define KEXEC_CORE_NOTE_NAME CRASH_CORE_NOTE_NAME
>
> +#ifndef CRASH_ALIGN
> +#define CRASH_ALIGN SZ_128M
> +#endif

Why 128M? Wouldn't we rather each architecture tells us its minimum alignment?


> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> index d714044..3492abd 100644
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -39,6 +39,8 @@
> #include <linux/compiler.h>
> #include <linux/hugetlb.h>
> #include <linux/frame.h>
> +#include <linux/memblock.h>
> +#include <linux/swiotlb.h>
>
> #include <asm/page.h>
> #include <asm/sections.h>
> @@ -96,6 +98,60 @@ int kexec_crash_loaded(void)
> }
> EXPORT_SYMBOL_GPL(kexec_crash_loaded);
>
> +int __init reserve_crashkernel_low(void)
> +{
> + unsigned long long base, low_base = 0, low_size = 0;
> + unsigned long total_low_mem;
> + int ret;
> +
> + total_low_mem = memblock_mem_size(1UL << (32 - PAGE_SHIFT));
> +
> + /* crashkernel=Y,low */
> + ret = parse_crashkernel_low(boot_command_line, total_low_mem,
> + &low_size, &base);
> + if (ret) {
> + /*
> + * two parts from lib/swiotlb.c:
> + * -swiotlb size: user-specified with swiotlb= or default.
> + *
> + * -swiotlb overflow buffer: now hardcoded to 32k. We round it
> + * to 8M for other buffers that may need to stay low too. Also
> + * make sure we allocate enough extra low memory so that we
> + * don't run out of DMA buffers for 32-bit devices.
> + */
> + low_size = max(swiotlb_size_or_default() + (8UL << 20),

SZ_8M?

> + 256UL << 20);

SZ_256M?


> + } else {
> + /* passed with crashkernel=0,low ? */
> + if (!low_size)
> + return 0;
> + }
> +
> + low_base = memblock_find_in_range(0, 1ULL << 32, low_size, CRASH_ALIGN);
> + if (!low_base) {
> + pr_err("Cannot reserve %ldMB crashkernel low memory, please try smaller size.\n",
> + (unsigned long)(low_size >> 20));
> + return -ENOMEM;
> + }
> +
> + ret = memblock_reserve(low_base, low_size);
> + if (ret) {
> + pr_err("%s: Error reserving crashkernel low memblock.\n",
> + __func__);
> + return ret;
> + }
> +
> + pr_info("Reserving %ldMB of low memory at %ldMB for crashkernel (System low RAM: %ldMB)\n",
> + (unsigned long)(low_size >> 20),
> + (unsigned long)(low_base >> 20),
> + (unsigned long)(total_low_mem >> 20));
> +
> + crashk_low_res.start = low_base;
> + crashk_low_res.end = low_base + low_size - 1;
> +
> + return 0;
> +}


Thanks,

James

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