[Xen-devel] kexec-ed kernel possibly needing low memory

["Jan Beulich" <JBeulich@xxxxxxxx>]

David,

we're being approached with the situation where a disk driver in the
kexec-ed kernel needs memory below 4G in order to perform DMA
(e.g. for the swiotlb to be set up). Linux not so long ago invented a
two area approach, which doesn't fit with the current single
KEXEC_RANGE_MA_CRASH area obtainable via
KEXEC_CMD_kexec_get_range.

I see multiple options
- do no change at all; the user can deal with this by explicitly
  specifying an area below 4G via "crashkernel="
- add KEXEC_RANGE_MA_CRASH_LOW
- when not asked for a specific address, always allocate the (single)
  area below 4G if there is enough space
- provide a means to request allocating the (single) area below 4G
  (or perhaps more generically below a certain boundary) without
  requiring an exact address to be specified

Do you have any preference here, or do you see other viable
alternatives?

Thanks, Jan


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