On 04/02/2020 01:49 PM, Dave Young wrote:
> On 03/26/20 at 06:07pm, James Morse wrote:
>> Memory added to the system by hotplug has a 'System RAM' resource created
>> for it. This is exposed to user-space via /proc/iomem.
>>
>> This poses problems for kexec on arm64. If kexec decides to place the
>> kernel in one of these newly onlined regions, the new kernel will find
>> itself booting from a region not described as memory in the firmware
>> tables.
>>
>> Arm64 doesn't have a structure like the e820 memory map that can be
>> re-written when memory is brought online. Instead arm64 uses the UEFI
>> memory map, or the memory node from the DT, sometimes both. We never
>> rewrite these.
>
> Could arm64 use similar way to update DT, or a cooked UEFI maps?
>
> Add pingfan in cc, he said ppc64 update the DT after a memremove thus it
> would be good to just redo a kexec load.
>
Yes, the memory changes will be observed through device-node under
/proc/device-tree/ (which is for powerpc).
Later if running kexec -l/-p , it can build new dtb with the latest info
from /proc/device-tree
> Added Pingfan and Hari for comments and corrections.
>
>>
>> Allow an architecture to specify a different name for these hotplug
>> regions.
>>
>> Signed-off-by: James Morse <james.morse@xxxxxxx>
>> ---
>> mm/memory_hotplug.c | 6 +++++-
>> 1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index 0a54ffac8c68..69b03dd7fc74 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -42,6 +42,10 @@
>> #include "internal.h"
>> #include "shuffle.h"
>>
>> +#ifndef MEMORY_HOTPLUG_RES_NAME
>> +#define MEMORY_HOTPLUG_RES_NAME "System RAM"
>> +#endif
>> +
>> /*
>> * online_page_callback contains pointer to current page onlining function.
>> * Initially it is generic_online_page(). If it is required it could be
>> @@ -103,7 +107,7 @@ static struct resource *register_memory_resource(u64 start, u64 size)
>> {
>> struct resource *res;
>> unsigned long flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
>> - char *resource_name = "System RAM";
>> + char *resource_name = MEMORY_HOTPLUG_RES_NAME;
>>
>> if (start + size > max_mem_size)
>> return ERR_PTR(-E2BIG);
>> --
>> 2.25.1
>>
>>
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>>
