[PATCH v24 5/9] arm64: kdump: add kdump support

[james.morse@arm.com (James Morse)]

On 22/08/16 02:29, AKASHI Takahiro wrote:
> On Fri, Aug 19, 2016 at 04:52:17PM +0530, Pratyush Anand wrote:
>> It will help kexec-tools to prevent copying  of any unnecessary data. I
>> think, then you also need to change phys_offset calculation in kexec-tools. That
>> should be start of either of first "reserved" or "System RAM" block.
> 
> Good point, but I'm not sure this is always true.

> Is there any system whose ACPI memory is *not* part of DRAM

>From the spec, it looks like this is allowed.

What do you mean by 'DRAM'? Any ACPI region will be in the UEFI memory map, so
the question is what is its type and memory attributes?
The UEFI spec[0] says ACPI regions can have a type of EfiACPIReclaimMemory or
EfiACPIMemoryNVS, the memory attributes aren't specified, so are chosen by the
firmware.

It is possible these regions have to be mapped non-cacheable, page 40 has a
couple of:
> If no information about the table location exists in the UEFI memory map or
ACPI memory
> descriptors, the table is assumed to be non-cached.

reserve_regions() in drivers/firmware/efi/arm-init.c will add any entry in the
memory map that has a 'WB' attribute to the memblock.memory list (via
early_init_dt_add_memory_arch()), it will also mark as no-map regions that have
this attribute and aren't in the is_reserve_region() list.

If these ACPI regions have the 'WB' attribute, we add them as memory and mark
them nomap. These show up as either a hole, or 'reserved' in /proc/iomem.
If they don't have the 'WB' attribute, then then they are left out of memblock
and aren't part of DRAM, I don't think these will show up in /proc/iomem at all.


Thanks,

James

[0] '2.3.6 AArch64 Platforms' of version 2.6 of the UEFI spec at
http://uefi.org/specifications