linux-kernel - Re: [PATCH v12 7/7] x86/crash: Add x86 crash hotplug support

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Message-ID: <43f16833-add1-80c3-3bf8-5a6a05e75be6@oracle.com>
Date:   Fri, 28 Oct 2022 16:22:54 -0500
From:   Eric DeVolder <eric.devolder@...cle.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Baoquan He <bhe@...hat.com>, david@...hat.com,
        Oscar Salvador <osalvador@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        kexec@...ts.infradead.org, ebiederm@...ssion.com,
        dyoung@...hat.com, vgoyal@...hat.com, tglx@...utronix.de,
        mingo@...hat.com, dave.hansen@...ux.intel.com, hpa@...or.com,
        nramas@...ux.microsoft.com, thomas.lendacky@....com,
        robh@...nel.org, efault@....de, rppt@...nel.org,
        sourabhjain@...ux.ibm.com, linux-mm@...ck.org
Subject: Re: [PATCH v12 7/7] x86/crash: Add x86 crash hotplug support



On 10/28/22 15:30, Borislav Petkov wrote:
> On Fri, Oct 28, 2022 at 02:26:58PM -0500, Eric DeVolder wrote:
>> config CRASH_MAX_MEMORY_RANGES
>>      depends on CRASH_DUMP && KEXEC_FILE && MEMORY_HOTPLUG
>>      int
>>      default 8192
>>      help
>>        For the kexec_file_load path, specify the maximum number of
>>        memory regions, eg. as represented by the 'System RAM' entries
>>        in /proc/iomem, that the elfcorehdr buffer/segment can accommodate.
>>        This value is combined with NR_CPUS and multiplied by Elf64_Phdr
>>        size to determine the final buffer size.
> 
> No, do this:
> 
> config CRASH_MEMORY_HOTPLUG_SUPPORT
>      depends on CRASH_DUMP && KEXEC_FILE && MEMORY_HOTPLUG
>      help
>        Help text explaining what this feature is
> 
> this thing will simply get enabled when the user enables MEMORY_HOTPLUG
> and CRASH_DUMP.
> 
> and then you do in the code:
> 
> /*
>   * A comment explaining how the 8192 value has been selected.
>   */
> #define CRASH_MAX_MEMORY_RANGES	8192
> 
> Thx.
> 

How is this comment?

/*
  * For the kexec_file_load() syscall path, specify the maximum number of
  * memory regions that the elfcorehdr buffer/segment can accommodate.
  * These regions are obtained via walk_system_ram_res(); eg. the
  * 'System RAM' entries in /proc/iomem.
  * This value is combined with NR_CPUS and multiplied by sizeof(Elf64_Phdr)
  * to determine the final elfcorehdr memory buffer/segment size.
  * The value 8192, for example, covers a (sparsely populated) 1TiB system
  * consisting of 128MiB memblock size, while resulting in an elfcorehdr
  * memory buffer/segment size under 1MiB.
  */
#define CRASH_MAX_MEMORY_RANGES 8192