[patch 0/7] unencrypted atomic DMA pools with dynamic expansion

[David Rientjes]

set_memory_decrypted() may block so it is not possible to do non-blocking
allocations through the DMA API for devices that required unencrypted
memory.

The solution is to expand the atomic DMA pools for the various possible
gfp requirements as a means to prevent an unnecessary depletion of lowmem.
These atomic pools are separated from the remap code and can be selected
for configurations that need them outside the scope of
CONFIG_DMA_DIRECT_REMAP, such as CONFIG_AMD_MEM_ENCRYPT.

These atomic DMA pools are kept unencrypted so they can immediately be
used for non-blocking allocations.  Since the need for this type of memory
depends on the kernel config and devices being used, these pools are also
dynamically expandable.

The sizes of the various atomic DMA pools is exported through debugfs at
/sys/kernel/debug/dma_pools.

This patchset is based on latest Linus HEAD:

commit 8632e9b5645bbc2331d21d892b0d6961c1a08429
Merge: 6cc9306b8fc0 f3a99e761efa
Author: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Date:   Tue Apr 14 11:58:04 2020 -0700

    Merge tag 'hyperv-fixes-signed' of git://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux
---
 arch/x86/Kconfig            |   1 +
 drivers/iommu/dma-iommu.c   |   5 +-
 include/linux/dma-direct.h  |   2 +
 include/linux/dma-mapping.h |   6 +-
 kernel/dma/Kconfig          |   6 +-
 kernel/dma/Makefile         |   1 +
 kernel/dma/direct.c         |  56 ++++++--
 kernel/dma/pool.c           | 275 ++++++++++++++++++++++++++++++++++++
 kernel/dma/remap.c          | 114 ---------------
 9 files changed, 334 insertions(+), 132 deletions(-)
 create mode 100644 kernel/dma/pool.c