On Thu, May 29, 2025, Kai Huang wrote: > On Thu, 2025-05-29 at 23:55 +1200, Kai Huang wrote: > > On Mon, 2025-05-19 at 16:28 -0700, Sean Christopherson wrote: > > > Add a Kconfig to allowing building KVM without support for emulating an > > ^ > > allow > > > > > I/O APIC, PIC, and PIT, which is desirable for deployments that effectively > > > don't support a fully in-kernel IRQ chip, i.e. never expect any VMM to > > > create an in-kernel I/O APIC. > > > > Do you happen to know what developments don't support a full in-kernel IRQ chip? Google Cloud, for one. I suspect/assume many/most CSPs don't utilize an in-kernel I/O APIC. > > Do they only support userspace IRQ chip, or not support any IRQ chip at all? The former, only userspace I/O APIC (and associated devices), though some VM shapes, e.g. TDX, don't provide an I/O APIC or PIC. > Forgot to ask: > > Since this new Kconfig option is not only for IOAPIC but also includes PIC and > PIT, is CONFIG_KVM_IRQCHIP a better name? I much prefer IOAPIC, because IRQCHIP is far too ambiguous and confusing, e.g. just look at KVM's internal APIs, where these: irqchip_in_kernel() irqchip_kernel() are not equivalent. In practice, no modern guest kernel is going to utilize the PIC, and the PIT isn't an IRQ chip, i.e. isn't strictly covered by IRQCHIP either. So I think/hope the vast majority of users/readers will be able to intuit that CONFIG_KVM_IOAPIC also covers the PIC and PIT.
