Nov 13 – 15, 2023
America/New_York timezone

RISC-V irqbypass with KVM

Nov 13, 2023, 12:45 PM
"James River Salon A" (Omni Richmond Hotel)

"James River Salon A"

Omni Richmond Hotel



Andrew Jones (Ventana Micro Systems)


KVM and VFIO provide an architecture-neutral irqbypass framework, but
its enablement requires an implementation of an architecture-specific
function, kvm_arch_irq_bypass_add_producer(). The RISC-V AIA and IOMMU
specifications provide novel support for guest interrupt delivery (most
notably MRIFs), which must be considered for RISC-V KVM's irqbypass
implementation. We have an initial proposal which includes the RISC-V
IOMMU driver implementing an IRQ domain in order to provide
irq_set_vcpu_affinity(). This discussion is seeking feedback on that
approach. Additionally, the RISC-V IOMMU will send notice MSIs when
guest vIMSICs are backed by MRIFs, requiring a policy to select where
the notice MSIs are delivered. This means we need to define new uAPI
in order to involve the user. Feedback on the uAPI proposals would
also be welcome. Also, we acknowledge that irqbypass performance will
differ for guests with assigned interrupt files vs. those with MRIFs
and we would like to discuss how best to modify or extend accounting in
order to improve accuracy of measurements. Finally, the PoC is just
getting started, by the time Plumbers meets, there should be enough
done to have made other design decisions which could be discussed.

Primary author

Andrew Jones (Ventana Micro Systems)

Presentation materials

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