Messages in this thread | | | Subject | Re: [PATCH 1/2] KVM: x86: implement KVM_SET_TSC_PRECISE/KVM_GET_TSC_PRECISE | From | Paolo Bonzini <> | Date | Mon, 30 Nov 2020 18:01:16 +0100 |
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On 30/11/20 16:58, Maxim Levitsky wrote: >> This is mostly useful for userspace that doesn't disable the quirk, right? > Isn't this the opposite? If I understand the original proposal correctly, > the reason that we include the TSC_ADJUST in the new ioctl, is that > we would like to disable the special kvm behavior (that is disable the quirk), > which would mean that tsc will jump on regular host initiated TSC_ADJUST write. > > To avoid this, userspace would set TSC_ADJUST through this new interface.
Yeah, that makes sense. It removes the need to think "I have to set TSC adjust before TSC".
> Do you think that this is an issue? If so I can make the code work with > signed numbers.
Not sure if it's an issue, but I prefer to make the API "less surprising" for userspace. Who knows how it will be used.
> About nsec == 0, this is to allow to use this API for VM initialization. > (That is to call KVM_SET_TSC_PRECISE prior to doing KVM_GET_TSC_PRECISE)
I prefer using flags for that purpose.
Paolo
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