kho: add support for preserving vmalloc allocations

From: "Mike Rapoport (Microsoft)" <[email protected]>

Hi,

Following the discussion about preservation of memfd with LUO [1] these patches add support for preserving vmalloc allocations.

Any KHO uses case presumes that there's a data structure that lists physical addresses of preserved folios (and potentially some additional metadata). Allowing vmalloc preservations with KHO allows scalable preservation of such data structures.

For instance, instead of allocating array describing preserved folios in the fdt, memfd preservation can use vmalloc:

        preserved_folios = vmalloc_array(nr_folios, sizeof(*preserved_folios));
        memfd_luo_preserve_folios(preserved_folios, folios, nr_folios);
        kho_preserve_vmalloc(preserved_folios, &folios_info);

[1] https://lore.kernel.org/all/[email protected]

v3 changes:
* rebase on mm-unstable

v2: https://lore.kernel.org/all/[email protected]
* support preservation of vmalloc backed by large pages
* add check for supported vmalloc flags and preserve the flags to be able to identify incompatible preservations
* don't use kho_preserve_phys()
* add kernel-doc

v1: https://lore.kernel.org/all/[email protected]

Mike Rapoport (Microsoft) (2):
kho: add support for preserving vmalloc allocations lib/test_kho: use kho_preserve_vmalloc instead of storing addresses in fdt

 include/linux/kexec_handover.h |  12 ++
 kernel/kexec_handover.c        | 200 +++++++++++++++++++++++++++++++++
 lib/test_kho.c                 |  41 +++++--
 3 files changed, 241 insertions(+), 12 deletions(-)

base-commit: b024763926d2726978dff6588b81877d000159c1

2.50.1