在 2019年10月15日 19:11, Eric W. Biederman 写道:
> lijiang <lijiang@xxxxxxxxxx> writes:
>
>> 在 2019年10月12日 20:16, Dave Young 写道:
>>> Hi Eric,
>>>
>>> On 10/12/19 at 06:26am, Eric W. Biederman wrote:
>>>> Lianbo Jiang <lijiang@xxxxxxxxxx> writes:
>>>>
>>>>> When the crashkernel kernel command line option is specified, the
>>>>> low 1MiB memory will always be reserved, which makes that the memory
>>>>> allocated later won't fall into the low 1MiB area, thereby, it's not
>>>>> necessary to create a backup region and also no need to copy the first
>>>>> 640k content to a backup region.
>>>>>
>>>>> Currently, the code related to the backup region can be safely removed,
>>>>> so lets clean up.
>>>>>
>>>>> Signed-off-by: Lianbo Jiang <lijiang@xxxxxxxxxx>
>>>>> ---
>>>>
>>>>> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
>>>>> index eb651fbde92a..cc5774fc84c0 100644
>>>>> --- a/arch/x86/kernel/crash.c
>>>>> +++ b/arch/x86/kernel/crash.c
>>>>> @@ -173,8 +173,6 @@ void native_machine_crash_shutdown(struct pt_regs *regs)
>>>>>
>>>>> #ifdef CONFIG_KEXEC_FILE
>>>>>
>>>>> -static unsigned long crash_zero_bytes;
>>>>> -
>>>>> static int get_nr_ram_ranges_callback(struct resource *res, void *arg)
>>>>> {
>>>>> unsigned int *nr_ranges = arg;
>>>>> @@ -234,9 +232,15 @@ static int prepare_elf64_ram_headers_callback(struct resource *res, void *arg)
>>>>> {
>>>>> struct crash_mem *cmem = arg;
>>>>>
>>>>> - cmem->ranges[cmem->nr_ranges].start = res->start;
>>>>> - cmem->ranges[cmem->nr_ranges].end = res->end;
>>>>> - cmem->nr_ranges++;
>>>>> + if (res->start >= SZ_1M) {
>>>>> + cmem->ranges[cmem->nr_ranges].start = res->start;
>>>>> + cmem->ranges[cmem->nr_ranges].end = res->end;
>>>>> + cmem->nr_ranges++;
>>>>> + } else if (res->end > SZ_1M) {
>>>>> + cmem->ranges[cmem->nr_ranges].start = SZ_1M;
>>>>> + cmem->ranges[cmem->nr_ranges].end = res->end;
>>>>> + cmem->nr_ranges++;
>>>>> + }
>>>>
>>>> What is going on with this chunk? I can guess but this needs a clear
>>>> comment.
>>>
>>> Indeed it needs some code comment, this is based on some offline
>>> discussion. cat /proc/vmcore will give a warning because ioremap is
>>> mapping the system ram.
>>>
>>> We pass the first 1M to kdump kernel in e820 as system ram so that 2nd
>>> kernel can use the low 1M memory because for example the trampoline
>>> code.
>>>
>> Thank you, Eric and Dave. I will add the code comment as below if it would be OK.
>>
>> @@ -234,9 +232,20 @@ static int prepare_elf64_ram_headers_callback(struct resource *res, void *arg)
>> {
>> struct crash_mem *cmem = arg;
>>
>> - cmem->ranges[cmem->nr_ranges].start = res->start;
>> - cmem->ranges[cmem->nr_ranges].end = res->end;
>> - cmem->nr_ranges++;
>> + /*
>> + * Currently, pass the low 1MiB range to kdump kernel in e820
>> + * as system ram so that kdump kernel can also use the low 1MiB
>> + * memory due to the real mode trampoline code.
>> + * And later, the low 1MiB range will be exclued from elf header,
>> + * which will avoid remapping the 1MiB system ram when dumping
>> + * vmcore.
>> + */
>> + if (res->start >= SZ_1M) {
>> + cmem->ranges[cmem->nr_ranges].start = res->start;
>> + cmem->ranges[cmem->nr_ranges].end = res->end;
>> + cmem->nr_ranges++;
>> + } else if (res->end > SZ_1M) {
>> + cmem->ranges[cmem->nr_ranges].start = SZ_1M;
>> + cmem->ranges[cmem->nr_ranges].end = res->end;
>> + cmem->nr_ranges++;
>> + }
>>
>> return 0;
>> }
>
> I just read through the appropriate section of crash.c and the way
> things are structured doing this work in
> prepare_elf64_ram_headers_callback is wrong.
>
> This can be done in a simpler manner in elf_header_exclude_ranges.
> Something like:
>
Thank you, Eric. It seems that here is a more reasonable place, i will make
a test about it and improve it in next post.
Lianbo
> /* The low 1MiB is always reserved */
> ret = crash_exclude_mem_range(cmem, 0, 1024*1024);
> if (ret)
> return ret;
>
> Eric
>
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