[PATCH 16/18] Documentation: KVM: Clarify that PMU_V3_IRQ IntID requirements for GICv5

[Marc Zyngier]

From: Sascha Bischoff <sascha.bischoff at arm.com>

When running a GICv5-based guest, the PMU must use PPI 23. This,
however, must be communicated via the
KVM_ARM_VCPU_PMU_V3_CTRL->KVM_ARM_VCPU_PMU_V3_IRQ ioctl as a full
GICv5-style Interrupt ID. That is, 0x20000017. Optionally, the whole
ioctl can be skipped for GICv5.

This was previously not clearly documented, so bump the documentation
accordingly.

Fixes: 7c31c06e2d2d ("KVM: arm64: gic-v5: Mandate architected PPI for PMU emulation on GICv5")
Link: https://sashiko.dev/#/patchset/20260319154937.3619520-1-sascha.bischoff%40arm.com
Signed-off-by: Sascha Bischoff <sascha.bischoff at arm.com>
Signed-off-by: Marc Zyngier <maz at kernel.org>
---
 Documentation/virt/kvm/devices/vcpu.rst | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/Documentation/virt/kvm/devices/vcpu.rst b/Documentation/virt/kvm/devices/vcpu.rst
index 5e38058200105..66e714f2fcfa7 100644
--- a/Documentation/virt/kvm/devices/vcpu.rst
+++ b/Documentation/virt/kvm/devices/vcpu.rst
@@ -37,8 +37,11 @@ Returns:
 A value describing the PMUv3 (Performance Monitor Unit v3) overflow interrupt
 number for this vcpu. This interrupt could be a PPI or SPI, but the interrupt
 type must be same for each vcpu. As a PPI, the interrupt number is the same for
-all vcpus, while as an SPI it must be a separate number per vcpu. For
-GICv5-based guests, the architected PPI (23) must be used.
+all vcpus, while as an SPI it must be a separate number per vcpu.
+
+For GICv5-based guests, the architected PPI (23) must be used, and must be
+communicated as the full GICv5-style Interrupt ID, i.e., 0x20000017. This ioctl
+can be omitted altogether for a GICv5-based guest.
 
 1.2 ATTRIBUTE: KVM_ARM_VCPU_PMU_V3_INIT
 ---------------------------------------
-- 
2.47.3