linux-kernel - [PATCH v2 0/8] ARM/ARM64 Direct EOI setup for VFIO platform interrupts

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Date:   Thu, 15 Jun 2017 14:52:32 +0200
From:   Eric Auger <eric.auger@...hat.com>
To:     eric.auger.pro@...il.com, eric.auger@...hat.com,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        kvmarm@...ts.cs.columbia.edu, alex.williamson@...hat.com,
        b.reynal@...tualopensystems.com, pbonzini@...hat.com,
        marc.zyngier@....com, christoffer.dall@...aro.org
Cc:     drjones@...hat.com, wei@...hat.com
Subject: [PATCH v2 0/8] ARM/ARM64 Direct EOI setup for VFIO platform interrupts

This series allows to optimize the deactivation of virtual interrupts
associated to vfio platform device interrupts.

This is a revival of "[PATCH v4 00/13] ARM IRQ forward control based on
IRQ bypass manager" (https://lkml.org/lkml/2015/11/19/351) whose development
was stalled due to dependency on new VGIC design and drop of priority.

Without that optimization the deactivation of the physical IRQ is performed
by the host. Also for level sensitive interrupts, The VFIO driver disables
the physical IRQ. The deactivation of the virtual IRQ by the guest is trapped
and the physical IRQ gets re-enabled at that time.

The ARM GIC supports direct EOI for virtual interrupts directly mapped
to physical interrupts. When this mode is set, the host does not
deactivate the physical interrupt anymore, but simply drops the
interrupt priority on EOI. When the guest deactivates the virtual IRQ,
the GIC automatically deactivates the physical IRQ. This avoids a world
switch on deactivation.

This series sets direct EOI mode on ARM/ARM64 for vfio platform interrupts.
This relies on a negotiation between the vfio platform driver and KVM/irqfd
though the irq bypass manager.

The setup sequence is:

preamble:
- disable the physical IRQ
- halt guest execution
forwarding setting:
- program the VFIO driver for forwarding (select the right physical
  interrupt handler)
- program the VGIC and IRQCHIP for forwarding
postamble:
- resume guest execution
- enable the physical IRQ

When destroying the optimized path the following sequence is executed:
- preamble
- unset forwarding at VGIC and IRQCHIP level
- unset forwarding at VFIO level
- postamble

The injection still is based on irqfd triggering. For level sensitive
interrupts though, the resamplefd is not triggered anymore since
deactivation is not trapped by KVM.

This was tested with:
- AMD Seattle xgmac platform device assignment
- Also MSI non regression was tested

The series can be fount at:
https://github.com/eauger/linux/tree/v4.12-rc5-deoi-v2

It is based on 4.12-rc5

Best Regards

Eric

History:
v1 -> v2:
- drop VFIO-PCI INTx support due to shared interrupt incompatibility
- introduce a producer type
- restructured kvm_vgic_[set|unset]_forwarding for reuse in forwarding
  setting

Eric Auger (8):
  VFIO: platform: Differentiate auto-masking from user masking
  VFIO: platform: Introduce direct EOI interrupt handler
  VFIO: platform: Direct EOI irq bypass for ARM/ARM64
  KVM: arm/arm64: vgic: restructure kvm_vgic_(un)map_phys_irq
  KVM: arm/arm64: vgic: Handle mapped level sensitive SPIs
  KVM: arm/arm64: vgic: Implement forwarding setting
  virt: irqbypass: Add a type field to the irqbypass producer
  KVM: arm/arm64: register DEOI irq bypass consumer on ARM/ARM64

 arch/arm/kvm/Kconfig                             |   3 +
 arch/arm64/kvm/Kconfig                           |   3 +
 drivers/vfio/pci/vfio_pci_intrs.c                |   1 +
 drivers/vfio/platform/Kconfig                    |   5 +
 drivers/vfio/platform/Makefile                   |   2 +-
 drivers/vfio/platform/vfio_platform_irq.c        |  60 ++++++---
 drivers/vfio/platform/vfio_platform_irq_bypass.c | 119 ++++++++++++++++
 drivers/vfio/platform/vfio_platform_private.h    |  30 ++++-
 include/kvm/arm_vgic.h                           |  13 +-
 include/linux/irqbypass.h                        |   7 +
 virt/kvm/arm/arch_timer.c                        |  24 +---
 virt/kvm/arm/arm.c                               |  48 +++++++
 virt/kvm/arm/vgic/vgic.c                         | 164 ++++++++++++++++++++---
 virt/kvm/arm/vgic/vgic.h                         |   7 +-
 14 files changed, 425 insertions(+), 61 deletions(-)
 create mode 100644 drivers/vfio/platform/vfio_platform_irq_bypass.c

-- 
2.5.5