On 2012-04-20 17:00, Eduardo Habkost wrote: > On Fri, Apr 20, 2012 at 12:12:38PM +0200, Jan Kiszka wrote: >> On 2012-04-19 22:03, Eduardo Habkost wrote: >>> Jan/Avi: ping? >>> >>> I would like to get this ABI detail clarified so it can be implemented >>> the right way on Qemu and KVM. >>> >>> My proposal is to simply add tsc-deadline to the data returned by >>> GET_SUPPORTED_CPUID, making KVM_CAP_TSC_DEADLINE_TIMER unnecessary. >>> >> >> IIRC, there were problems with this model to exclude that the feature >> gets reported this way without ensuring that in-kernel irqchip is >> actually activated. Please browse the discussions, it should be >> documented there. > > The flag was never added to GET_SUPPORTED_CPUID on any of the git > repositories I have checked, and I don't see that being done anywhere on > my KVM mailing list archives, either. So I don't see how we could have > had issues with GET_SUPPORTED_CPUID, if it was never present on the > code. > > What was present on the code before the fix, was coded that > unconditinally enabled the flag even if Qemu never asked for it, and > that really was wrong. > > GET_SUPPORTED_CPUID doesn't enable any flag: it just tells userspace > that the hardware and KVM supports the feature (and, surprise, this is > exactly what KVM_CAP_TSC_DEADLINE_TIMER means too, isn't it?). It's up > to userspace to enable the CPUID bits according to user requirements and > userspace capabilities (in other words: only when userspace knows it is > safe because the in-kernel irqchip is enabled). > > If the above is not what GET_SUPPORTED_CPUID means, I would like to get > that clarified, so I can submit an updated to KVM API documentation. Does old userspace filter out flags from GET_SUPPORTED_CPUID that it does not understand? Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux -- 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
