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.
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