On 2016-04-26 16:59, Radim Krčmář wrote: > 2016-04-26 16:24+0200, Jan Kiszka: >> On 2016-04-26 13:40, Peter Xu wrote: >>> Currently, all the interrupts will be translated into one MSI in >>> vtd_generate_msi_message(), in which only 8 bits of dest_id is used >>> (msg.dest = irq->dest). We may possibly need to use the high 32 bits >>> of MSI address to store the rest dest[31:8]? Don't know whether this >>> would be enough though. >> >> Yes, I ran into this topic as well as I hacked up those line. Currently, >> KVM does not support more than 254 vCPUs, so 8 bits of those 32 are >> actually fine, and piggy-backing them in an MSI message works. >> >> Once KVM supports more CPUs, it has to come up with a new userspace >> interface to inject APIC events for more than 255 CPUs. Maybe the >> existing direct MSI inject with its unused flags could be "bended", >> maybe there are already better ideas (Radim?). > > Adding a flag to msi_msg and taking 3-4 bytes from padding to express > x2APIC addresses is reasonable. (It is what my prototype did. :]) > > The conceptually different idea is forcing all userspace interrupts > through irqfd routes, which would obsolete the ad-host inject.
irqfd for userspace sources is a bit clumsy from the API POV. On the other hand, we need to tweak the routing API anyway to achieve the same address extension there, too. Jan > >> In any case, the KVM layer in userspace will then have to pick up all 32 >> destination bits from the IRTE and deliver them via that new interface >> to the in-kernel APICs. > > I'll keep that in mind, thanks. >
