[PATCH v26 0/7] arm64: add kdump support

On 19 September 2016 at 17:05, James Morse [off-list ref] wrote:

On 16/09/16 21:17, Ard Biesheuvel wrote:

quoted

On 16 September 2016 at 17:04, James Morse [off-list ref] wrote:

quoted

Mark, Ard, how does/will reserved-memory work on an APCI only system?

It works by accident, at the moment. We used to ignore both
/memreserve/s and the /reserved-memory node, but due to some unrelated
refactoring, we ended up honouring the reserved-memory node when
booting via UEFI

Okay, so kdump probably shouldn't rely on this behaviour...

No, but I would still like to keep /reserved-memory node support for
dynamic ranges, since they are guaranteed not to contain anything
'magic' left behind by the firmware. So if we keep /that/, keeping
static allocation support (with validation, as I proposed in the
series I quoted) is only a small step.

-- 
Ard.

For an acpi-only system, we could get reserve_crashkernel() to copy the uefi
memory map into the reserved region, changing the region types for existing
kernel memory to EfiReservedMemoryType (for example) and fixing up the reserved
region boundaries.

This second memory map could then be added alongside the real one in the
DT/chosen, and used in preference the second time we go through uefi_init() in
the crash kernel.

kexec-tools would still need to keep the '/reserved-memory' node for non-uefi
systems.

Doing this doesn't depend on userspace, and means the uefi memory map is still
the one and only true source of memory layout information. If fixing it like
this is valid I don't think it should block kdump.

... I will think about this some more before trying to put it together.



Thanks,

James