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...rrectly to > the L2 guest when L0 is hyperv. KVM could pass *hyperv's* clock, but > L1 isn't notified when the data structure changes, so how the heck is > it supposed to update the kvmclock structure? Well, this kind of works in the the followin way: L1's clocksource is 'tsc_page' which is, basically, a compliment to TSC: two numbers provided by L0: offset and scale and KVM was tought to treat this clocksource as a good one (see b0c39dc68e3b "x86/kvm: Pass stable clocksource to guests when running nested on Hyper-V"). The notification you're talking about...

...rrectly to > the L2 guest when L0 is hyperv. KVM could pass *hyperv's* clock, but > L1 isn't notified when the data structure changes, so how the heck is > it supposed to update the kvmclock structure? Well, this kind of works in the the followin way: L1's clocksource is 'tsc_page' which is, basically, a compliment to TSC: two numbers provided by L0: offset and scale and KVM was tought to treat this clocksource as a good one (see b0c39dc68e3b "x86/kvm: Pass stable clocksource to guests when running nested on Hyper-V"). The notification you're talking about...

...est when L0 is hyperv. KVM could pass *hyperv's* clock, but > > L1 isn't notified when the data structure changes, so how the heck is > > it supposed to update the kvmclock structure? > > Well, this kind of works in the the followin way: > L1's clocksource is 'tsc_page' which is, basically, a compliment to TSC: > two numbers provided by L0: offset and scale and KVM was tought to treat > this clocksource as a good one (see b0c39dc68e3b "x86/kvm: Pass stable > clocksource to guests when running nested on Hyper-V"). > > The notification...

...guest when L0 is hyperv. KVM could pass *hyperv's* clock, but >> L1 isn't notified when the data structure changes, so how the heck is >> it supposed to update the kvmclock structure? > > Well, this kind of works in the the followin way: > L1's clocksource is 'tsc_page' which is, basically, a compliment to TSC: > two numbers provided by L0: offset and scale and KVM was tought to treat > this clocksource as a good one (see b0c39dc68e3b "x86/kvm: Pass stable > clocksource to guests when running nested on Hyper-V"). > > The notification...

Matt attempted to add CLOCK_TAI support to the VDSO clock_gettime() implementation, which extended the clockid switch case and added yet another slightly different copy of the same code. Especially the extended switch case is problematic as the compiler tends to generate a jump table which then requires to use retpolines. If jump tables are disabled it adds yet another conditional to the existing

Matt attempted to add CLOCK_TAI support to the VDSO clock_gettime() implementation, which extended the clockid switch case and added yet another slightly different copy of the same code. Especially the extended switch case is problematic as the compiler tends to generate a jump table which then requires to use retpolines. If jump tables are disabled it adds yet another conditional to the existing