[PATCH 0/8] Make PDX compression optional

[Alejandro Vallejo <alejandro.vallejo@xxxxxxxxx>]

Currently there's a CONFIG_HAS_PDX Kconfig option, but it's impossible to
disable it because the whole codebase performs unconditional
compression/decompression operations on addresses. This has the
unfortunate side effect that systems without a need for compression still
have to pay the performance impact of juggling bits on every pfn<->pdx
conversion (this requires reading several global variables). This series
attempts to:

  * Leave the state of pdx and pdx compression documented
  * Factor out compression so it _can_ be removed through Kconfig
  * Make it so compression is disabled on x86 and enabled on both Aarch32
    and Aarch64 by default.

Series summary:

Patch 1 documents the current general understanding of the pdx concept and
        pdx compression in particular
Patch 2 makes a clarification in ARM code to explain some discrepancies
        between the concept of "directmap" in arm32 and arm64 relevant to
        this series (i.e: why this series doesn't touch arm32 in directmap
        accesses).
Patch 3 Marks the pdx compression globals as ro_after_init
Patch 4 Gets rid of the current CONFIG_HAS_PDX option because (a) the name
        is misleading (b) cannot be removed in its current form.
Patch 5 Moves hard-coded compression-related logic to helper functions
Patch 6 Refactors all instances of regions being validated for pdx
        compression conformance so it's done through a helper
Patch 7 Non-functional reorder in order to simplify the patch 8 diff
Patch 8 Adds new Kconfig option to compile out PDX compression

Alejandro Vallejo (8):
  mm/pdx: Add comments throughout the codebase for pdx
  arm/mm: Document the differences between arm32 and arm64 directmaps
  pdx: Mark pdx hole description globals readonly after boot
  build: Remove CONFIG_HAS_PDX
  mm: Factor out the pdx compression logic in ma/va converters
  mm/pdx: Standardize region validation wrt pdx compression
  pdx: Reorder pdx.[ch]
  pdx: Add CONFIG_HAS_PDX_COMPRESSION as a Kconfig option

 xen/arch/arm/Kconfig                   |   1 -
 xen/arch/arm/include/asm/mm.h          |  30 ++-
 xen/arch/x86/Kconfig                   |   1 -
 xen/arch/x86/domain.c                  |  19 +-
 xen/arch/x86/include/asm/x86_64/page.h |  28 ++-
 xen/arch/x86/x86_64/mm.c               |   2 +-
 xen/common/Kconfig                     |  13 +-
 xen/common/Makefile                    |   2 +-
 xen/common/efi/boot.c                  |   6 +-
 xen/common/pdx.c                       | 120 +++++++++---
 xen/include/xen/mm.h                   |  11 ++
 xen/include/xen/pdx.h                  | 241 +++++++++++++++++++++++--
 12 files changed, 405 insertions(+), 69 deletions(-)

-- 
2.34.1