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. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
