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:
/* The low 1MiB is always reserved */
ret = crash_exclude_mem_range(cmem, 0, 1024*1024);
if (ret)
return ret;
Eric
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