On Thu, 15 May 2025 11:30:33 +0100, Ben Horgan <ben.horgan@xxxxxxx> wrote: > > Hi, > > On 5/14/25 20:21, Raghavendra Rao Ananta wrote: > > 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. > What's the reason for the cmdline enable continuing to be absolute in > the disable case? I wonder if this is unnecessarily restrictive. Because there are a number of GICv4 implementations that are absolutely terrible out there, and that will happily lock-up under some undisclosed circumstances. So unless you find a good way to retire that HW, GICv4 will continue to be a buy-in. M. -- Without deviation from the norm, progress is not possible.
