linux-kernel - generic DMA bypass flag v4

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Date:   Wed,  8 Jul 2020 17:24:44 +0200
From:   Christoph Hellwig <hch@....de>
To:     iommu@...ts.linux-foundation.org,
        Alexey Kardashevskiy <aik@...abs.ru>
Cc:     linuxppc-dev@...ts.ozlabs.org, Lu Baolu <baolu.lu@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Joerg Roedel <joro@...tes.org>,
        Robin Murphy <robin.murphy@....com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Björn Töpel <bjorn.topel@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        linux-kernel@...r.kernel.org
Subject: generic DMA bypass flag v4

Hi all,

I've recently beeing chatting with Lu about using dma-iommu and
per-device DMA ops in the intel IOMMU driver, and one missing feature
in dma-iommu is a bypass mode where the direct mapping is used even
when an iommu is attached to improve performance.  The powerpc
code already has a similar mode, so I'd like to move it to the core
DMA mapping code.  As part of that I noticed that the current
powerpc code has a little bug in that it used the wrong check in the
dma_sync_* routines to see if the direct mapping code is used.

These two patches just add the generic code and move powerpc over,
the intel IOMMU bits will require a separate discussion.

The x86 AMD Gart code also has a bypass mode, but it is a lot
strange, so I'm not going to touch it for now.

Note that as-is this breaks the XSK buffer pool, which unfortunately
poked directly into DMA internals.  A fix for that is already queued
up in the netdev tree.

Jesper and XDP gang: this should not regress any performance as
the dma-direct calls are now inlined into the out of line DMA mapping
calls.  But if you can verify the performance numbers that would be
greatly appreciated.

A git tree is available here:

    git://git.infradead.org/users/hch/misc.git dma-bypass.4

Gitweb:

    git.infradead.org/users/hch/misc.git/shortlog/refs/heads/dma-bypass.4

Changes since v3:
 - add config options for the dma ops bypass and dma ops themselves
   to not increase the size of tinyconfig builds

Changes since v2:
 - move the dma mapping helpers out of line
 - check for possible direct mappings using the dma mask

Changes since v1:
 - rebased to the current dma-mapping-for-next tree

Diffstat:
 arch/alpha/Kconfig                |    1 
 arch/arm/Kconfig                  |    1 
 arch/ia64/Kconfig                 |    1 
 arch/mips/Kconfig                 |    1 
 arch/parisc/Kconfig               |    1 
 arch/powerpc/Kconfig              |    2 
 arch/powerpc/include/asm/device.h |    5 
 arch/powerpc/kernel/dma-iommu.c   |   90 +------------
 arch/s390/Kconfig                 |    1 
 arch/sparc/Kconfig                |    1 
 arch/x86/Kconfig                  |    1 
 drivers/iommu/Kconfig             |    2 
 drivers/misc/mic/Kconfig          |    1 
 drivers/vdpa/Kconfig              |    1 
 drivers/xen/Kconfig               |    1 
 include/linux/device.h            |   11 +
 include/linux/dma-direct.h        |  104 +++++++++++++++
 include/linux/dma-mapping.h       |  251 ++++----------------------------------
 kernel/dma/Kconfig                |   12 +
 kernel/dma/Makefile               |    3 
 kernel/dma/direct.c               |   74 -----------
 kernel/dma/mapping.c              |  214 ++++++++++++++++++++++++++++++--
 22 files changed, 385 insertions(+), 394 deletions(-)