[PATCH v2 0/1] Remove the need to alloc memory in uv.c

[Harald Freudenberger <freude@linux.ibm.com>]

The pkey uv handler may be called in a do-not-allocate memory
situation. For example when an encrypted swap file is used and the
encryption is done via UV retrievable secrets with protected keys.

The pkey uv handler calls uv_get_secret_metadata() and thus has a need
to have this function work without memory allocations. So this patch
extends the uv_get_secret_metadata() function to be able to work on
a provided working page instead of allocating/freeing memory via
kmalloc/kfree:

int uv_get_secret_metadata(const u8 secret_id[UV_SECRET_ID_LEN],
			   struct uv_secret_list_item_hdr *secret,
			   u8 *workpage);

Parameter workpage is a ephemeral working page used by the function.
If given (!= NULL), it needs to point to memory of at least PAGE_SIZE
bytes. If NULL, the function uses kmalloc/kfree to allocate and free a
working buffer.

Changelog:
v1: Pre-allocated one page during init of the uv.c code.
v2: As a result of feedback from Heiko about the v1 implementation and
    with another idea of how to deal with a do-not-allocate situation
    in uv.c now another approach: The caller may give a ptr to an
    ephemeral working page if no memory may be allocated.
    Note this patch does not compile as pkey_uv.c needs to get
    adapted to this changed uv function. However, patch is good as a
    starting point for code review and discussions.
    
Harald Freudenberger (1):
  s390/uv: New param workpage for the uv_get_secret_metadata() function

 arch/s390/include/asm/uv.h |  3 ++-
 arch/s390/kernel/uv.c      | 12 +++++++++---
 2 files changed, 11 insertions(+), 4 deletions(-)

--
2.43.0