linux-kernel - [rfc 0/6] unencrypted atomic DMA pools with dynamic expansion

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Date:   Sun, 1 Mar 2020 16:05:03 -0800 (PST)
From:   David Rientjes <rientjes@...gle.com>
To:     Christoph Hellwig <hch@....de>,
        Tom Lendacky <thomas.lendacky@....com>
cc:     "Singh, Brijesh" <brijesh.singh@....com>,
        "Grimm, Jon" <jon.grimm@....com>, Joerg Roedel <joro@...tes.org>,
        baekhw@...gle.com,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>
Subject: [rfc 0/6] unencrypted atomic DMA pools with dynamic expansion

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 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.

Some of these patches could be squashed into each other, but they were
separated out to ease code review.

This patchset is based on 5.6-rc4.
---
 arch/x86/Kconfig            |   1 +
 drivers/iommu/dma-iommu.c   |   5 +-
 include/linux/dma-direct.h  |   2 +
 include/linux/dma-mapping.h |   6 +-
 kernel/dma/direct.c         |  17 ++--
 kernel/dma/remap.c          | 173 +++++++++++++++++++++++++-----------
 6 files changed, 140 insertions(+), 64 deletions(-)