Gleb Natapov wrote on 2012-12-25: > On Tue, Dec 25, 2012 at 06:42:59AM +0000, Zhang, Yang Z wrote: >> Gleb Natapov wrote on 2012-12-25: >>> On Mon, Dec 24, 2012 at 11:53:37PM +0000, Zhang, Yang Z wrote: >>>> Gleb Natapov wrote on 2012-12-24: >>>>> On Mon, Dec 24, 2012 at 02:35:35AM +0000, Zhang, Yang Z wrote: >>>>>> Zhang, Yang Z wrote on 2012-12-24: >>>>>>> Gleb Natapov wrote on 2012-12-20: >>>>>>>> On Mon, Dec 17, 2012 at 01:30:50PM +0800, Yang Zhang wrote: >>>>>>>>> basically to benefit from apicv, we need clear MSR bitmap for >>>>>>>>> corresponding x2apic MSRs: >>>>>>>>> 0x800 - 0x8ff: no read intercept for apicv register virtualization >>>>>>>>> TPR,EOI,SELF-IPI: no write intercept for virtual interrupt delivery >>>>>>>> We do not set "Virtualize x2APIC mode" bit in secondary execution >>>>>>>> control. If I read the spec correctly without that those MSR read/writes >>>>>>>> will go straight to physical local APIC. >>>>>>> Right. Now it cannot get benefit, but we may enable it in future and >>>>>>> then we can benefit from it. >>>>> Without enabling it you cannot disable MSR intercept for x2apic MSRs. >>>>> >>>>>> how about to add the following check: >>>>>> if (apicv_enabled && virtual_x2apic_enabled) >>>>>> clear_msr(); >>>>>> >>>>> I do not understand what do you mean here. >>>> In this patch, it will clear MSR bitmap(0x800 -0x8ff) when apicv enabled. As > you >>> said, since kvm doesn't set "virtualize x2apic mode", APIC register >>> virtualization never take effect. So we need to clear MSR bitmap only >>> when apicv enabled and virtualize x2apic mode set. >>>> >>> But currently it is never set. >> So you think the third patch is not necessary currently? Unless we >> enabled "virtualize x2apic mode". >> > Without third patch vid will not work properly if a guest is in x2apic > mode. Actually second and third patches need to be reordered to not have > a windows where x2apic is broken. The problem is that this patch itself > is buggy since it does not set "virtualize x2apic mode" flag. It should > set the flag if vid is enabled and if the flag cannot be set vid should > be forced off. In what conditions this flag cannot be set? I think the only case is that KVM doesn't expose the x2apic capability to guest, if this is true, the guest will never use x2apic and we still can use vid. Best regards, Yang -- 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
