Hi, On 21/07/2016 19:15, Radim Krčmář wrote: > 2016-07-21 17:43+0100, Andre Przywara: >> Hi Radim, >> >> On 21/07/16 17:01, Radim Krčmář wrote: >>> 2016-07-18 13:25+0000, Eric Auger: >>>> On ARM, the MSI msg (address and data) comes along with >>>> out-of-band device ID information. The device ID encodes the >>>> device that writes the MSI msg. Let's convey the device id in >>>> kvm_irq_routing_msi and use KVM_MSI_VALID_DEVID flag value in >>>> kvm_irq_routing_entry to indicate the msi devid is populated. >>>> >>>> Signed-off-by: Eric Auger <eric.auger@xxxxxxxxxx> >>>> Reviewed-by: Andre Przywara <andre.przywara@xxxxxxx> >>>> >>>> --- >>>> >>>> +devid: If KVM_MSI_VALID_DEVID is set, contains a unique device identifier >>>> + for the device that wrote the MSI message. >>>> + For PCI, this is usually a BFD identifier in the lower 16 bits. >>>> + >>>> +The per-VM KVM_CAP_MSI_DEVID capability advertises the requirement to >>>> +provide the device ID. If this capability is not set, userland cannot >>>> +rely on the kernel to allow the KVM_MSI_VALID_DEVID flag being set. >>> >>> It would be better to enforce this mentioned dependency on set >>> KVM_CAP_MSI_DEVID, but is the dependency even required? >>> It seems we were checking flags for zero, so KVM_MSI_VALID_DEVID >>> couldn't have been set by old userspaces, therefor it is ok to only make >>> it depend only on the presence of KVM_CAP_MSI_DEVID, like the patch does >>> now. (I assume KVM_MSI_VALID_DEVID and KVM_CAP_MSI_DEVID are being >>> merged at the same time.) >>> >>> Then there would be little point in having KVM_CAP_MSI_DEVID enableable, >>> so does enabling KVM_CAP_MSI_DEVID mean that every MSI must have a valid >>> devid? >> >> KVM_CAP_MSI_DEVID tells userland that it's fine to set the >> KVM_MSI_VALID_DEVID flag (because the kernel would bark otherwise). >> >> KVM_MSI_VALID_DEVID tells the kernel that there is some meaningful >> device ID data in the field formerly known as "pad". >> >> IIRC we started with the VALID_DEVID flag, then found that we need the >> CAP because we repurposed the pad field. >> >> Does that make sense? Admittedly this _is_ confusing ;-) > > It does, thanks. > Some capability is need and I thought that KVM_CAP_MSI_DEVID has to be > enabled by userspace before KVM_MSI_VALID_DEVID can be used, which isn't > the case. It is enabled conditionally based on vgic ITS ... my bad. > Great Thanks Andre for the clarification Eric _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
