linux-kernel - [PATCH v3 0/2] Fix coherence for VMbus and PCI pass-thru devices in Hyper-V VM

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Date:   Thu, 24 Mar 2022 09:14:50 -0700
From:   Michael Kelley <mikelley@...rosoft.com>
To:     sthemmin@...rosoft.com, kys@...rosoft.com, haiyangz@...rosoft.com,
        wei.liu@...nel.org, decui@...rosoft.com, rafael@...nel.org,
        lenb@...nel.org, lorenzo.pieralisi@....com, robh@...nel.org,
        kw@...ux.com, bhelgaas@...gle.com, hch@....de,
        m.szyprowski@...sung.com, robin.murphy@....com,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hyperv@...r.kernel.org, linux-pci@...r.kernel.org,
        iommu@...ts.linux-foundation.org
Cc:     mikelley@...rosoft.com
Subject: [PATCH v3 0/2] Fix coherence for VMbus and PCI pass-thru devices in Hyper-V VM

Hyper-V VMs have VMbus synthetic devices and PCI pass-thru devices that are added
dynamically via the VMbus protocol and are not represented in the ACPI DSDT. Only
the top level VMbus node exists in the DSDT. As such, on ARM64 these devices don't
pick up coherence information and default to not hardware coherent.  This results
in extra software coherence management overhead since the synthetic devices are
always hardware coherent. PCI pass-thru devices are also hardware coherent in all
current usage scenarios.

Fix this by propagating coherence information from the top level VMbus node in
the DSDT to all VMbus synthetic devices and PCI pass-thru devices. While smaller
granularity of control would be better, basing on the VMbus node in the DSDT
gives as escape path if a future scenario arises with devices that are not
hardware coherent.

Changes since v2:
* Move coherence propagation for VMbus synthetic devices to a separate
  .dma_configure function instead of the .probe fucntion [Robin Murphy]

Changes since v1:
* Use device_get_dma_attr() instead of acpi_get_dma_attr(), eliminating the
  need to export acpi_get_dma_attr() [Robin Murphy]
* Use arch_setup_dma_ops() to set device coherence [Robin Murphy]
* Move handling of missing _CCA to vmbus_acpi_add() so it is only done once
* Rework handling of PCI devices so existing code in pci_dma_configure()
  just works

Michael Kelley (2):
  Drivers: hv: vmbus: Propagate VMbus coherence to each VMbus device
  PCI: hv: Propagate coherence from VMbus device to PCI device

 drivers/hv/hv_common.c              | 11 +++++++++++
 drivers/hv/vmbus_drv.c              | 31 +++++++++++++++++++++++++++++++
 drivers/pci/controller/pci-hyperv.c |  9 +++++++++
 include/asm-generic/mshyperv.h      |  1 +
 4 files changed, 52 insertions(+)

-- 
1.8.3.1