Hi Christoffer, On 06/07/15 10:30, Christoffer Dall wrote: > On Mon, Jul 06, 2015 at 09:30:20AM +0100, Andre Przywara wrote: >> Hi Pavel, >> >> On 06/07/15 07:42, Pavel Fedin wrote: >>> Hello! >>> >>>> I like this approach, but it runs into problems: >>>> As you read above the current documentation says that the flags field >>>> must be zero and the current KVM_SET_GSI_ROUTING handler bails out if it >>>> isn't. So userland would need to know whether it's safe to set that >>>> field. >>> >>> This problem does not exist because: >>> a) Older platforms do not need this flag, so they expect to get zero. >>> b) ARM64 + GICv3 platform cannot work without this flag. >>> >>> This is perfectly OK combination IMO. Userland just knows, whether it needs to supply device ID or >>> not. For example, my modified qemu now has kvm_msi_flags global variable which defaults to 0. ITS >>> code, then, if activated, changes it to KVM_MSI_VALID_DEVID, and qemu starts supplying device IDs to >>> the related calls. >> >> Well, I had this solution before in kvmtool: If ARM && ITS then set the >> flag. But I wasn't really happy with this, as the IRQ routing, setup and >> injection code is rather architecture agnostic (implementing the generic >> KVM interface), so spraying in some architecture hacks sounded not very >> elegant. >> Also as the flag describes a rather generic feature (provide an unique >> device ID), I'd rather avoid to make this an ARM hack. >> >> That being said this is not a show stopper for me, so if the others are >> happy with this, I will go down your road. >> > There must be some way for userspace to discover if it's valid to set > the flag or not; either through a well-defined error-code probing > mechanism for KVM_SET_GSI_ROUTING or through advertising a capability. Right, makes sense, I was wondering about this requirement earlier, but couldn't find really good prior art in the code (KVM_GET_VCPU_EVENTS seems to be bad example). So I think we get along with a new VM specific capability like KVM_CAP_MSIS_REQUIRE_DEVID. This isn't strictly a "capability" (as it's more a requirement), but I guess it fits here anyway. It has to be per-VM, as a GICv2M guest does not need it, but an ITS guest does. We can use this very flag for both the KVM_SIGNAL_MSI and the KVM_SET_GSI_ROUTING ioctl, so interface churn is kept minimal. Does that make sense? Actually I have implemented this already last week, I will send it out along with a v2 of the ITS emulation later this week. Cheers, Andre. _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
