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

Thanks for your review.

On 2019/6/6 0:29, James Morse wrote:
> 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?
>
> [...]

At present, reserve_crashkernel_low() is called only when reserving crashkernel above 4G, so i deleted
this #ifdef.
If we called reserve_crashkernel_low() at the beginning of reserve_crashkernel(), i need to add it back.

>
>
>> @@ -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?

Yeah, each architecture should tells us its minimum alignment. I added this default size to
fix compiling error on some architecture which didn't define it. I will add x86_64 and arm64
restriction on reserve_crashkernel_low() and delete this define.

>
>
>> 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?
>

There is compiling warning "warning: comparison of distinct pointer types lacks a cast" if just use
SZ_8M or SZ_256M. We need cast swiotlb_size_or_default() to type int,so i kept the old as in x86_64.

>
>> + } 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
>
> .
>

Thanks,
Chen Zhou

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