linux-kernel - [PATCH 0/3] KVM: arm64: Allow vGICv4 configuration per VM

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Message-ID: <20250514192159.1751538-1-rananta@google.com>
Date: Wed, 14 May 2025 19:21:56 +0000
From: Raghavendra Rao Ananta <rananta@...gle.com>
To: Oliver Upton <oliver.upton@...ux.dev>, Marc Zyngier <maz@...nel.org>
Cc: Raghavendra Rao Anata <rananta@...gle.com>, Mingwei Zhang <mizhang@...gle.com>, 
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: [PATCH 0/3] KVM: arm64: Allow vGICv4 configuration per VM

Hello,

When kvm-arm.vgic_v4_enable=1, KVM adds support for direct interrupt
injection by default to all the VMs in the system, aka GICv4. A
shortcoming of the GIC architecture is that there's an absolute limit on
the number of vPEs that can be tracked by the ITS. It is possible that
an operator is running a mix of VMs on a system, only wanting to provide
a specific class of VMs with hardware interrupt injection support.

To support this, introduce a GIC attribute, KVM_DEV_ARM_VGIC_CONFIG_GICV4,
for the userspace to enable or disable vGICv4 for a given VM.

The attribute allows the configuration only when vGICv4 is enabled in KVM,
else it acts a read-only attribute returning
KVM_DEV_ARM_VGIC_CONFIG_GICV4_UNAVAILABLE as the value.

On the other hand, if KVM has the vGICv4 enabled via the cmdline, the
VM absorbs this configuration by default to maintain the backward
compatibility. Userspace can get the attribute's value to check if the VM
has vGICv4 support if it sees KVM_DEV_ARM_VGIC_CONFIG_GICV4_ENABLE as the
value. As required, it can disable vGICv4 by setting
KVM_DEV_ARM_VGIC_CONFIG_GICV4_DISABLE as the value.

The patches are distrubuted as:

Patch-1 contains the KVM code that introduces the
KVM_DEV_ARM_VGIC_CONFIG_GICV4 attr, and adds all the support around it.

Patch-2 adds the documentation for the said attribute.

Patch-3 extends the vgic_init kvm/arm64 selftest that tests the get and
set of this attribute in various configurations.

Thank you.
Raghavendra

Raghavendra Rao Ananta (3):
  kvm: arm64: Add support for KVM_DEV_ARM_VGIC_CONFIG_GICV4 attr
  docs: kvm: devices/arm-vgic-v3: Document KVM_DEV_ARM_VGIC_CONFIG_GICV4
    attr
  KVM: selftests: Extend vgic_init to test GICv4 config attr

 .../virt/kvm/devices/arm-vgic-v3.rst          | 24 ++++++--
 arch/arm64/include/uapi/asm/kvm.h             |  7 +++
 arch/arm64/kvm/vgic/vgic-init.c               |  3 +
 arch/arm64/kvm/vgic/vgic-its.c                |  2 +-
 arch/arm64/kvm/vgic/vgic-kvm-device.c         | 39 +++++++++++++
 arch/arm64/kvm/vgic/vgic-mmio-v3.c            | 12 ++--
 arch/arm64/kvm/vgic/vgic-v3.c                 | 16 ++++-
 arch/arm64/kvm/vgic/vgic-v4.c                 |  8 +--
 include/kvm/arm_vgic.h                        |  5 ++
 tools/testing/selftests/kvm/arm64/vgic_init.c | 58 +++++++++++++++++++
 10 files changed, 157 insertions(+), 17 deletions(-)

base-commit: 0af2f6be1b4281385b618cb86ad946eded089ac8
--
2.49.0.1101.gccaa498523-goog