Messages in this thread | | | Date | Wed, 4 Oct 2023 11:29:13 -0400 | From | Tyler Stachecki <> | Subject | Re: [PATCH 0/5] KVM: x86: Fix breakage in KVM_SET_XSAVE's ABI |
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On Wed, Oct 04, 2023 at 07:51:17AM -0700, Sean Christopherson wrote: > KVM's ABI has no formal notion of guest boot=>shutdown or live migration. The > myriad KVM_GET_* APIs allow taking a snapshot of guest state, and the KVM_SET_* > APIs allow loading a snapshot of guest state. Live migration is probably the most > common use of those APIs, but there are other use cases.
I think the lightbulb just clicked, it is really this:
> No, the VM will not have less features, because KVM_SET_XSAVE loads *data*, not > features [...]
I think I'm conflating the data vs. features aspect here and will have to revisit my understanding of the code...
> > Ultimately, this problem is not really fixable if said features cannot be > > removed.
> It's not about removing features. The change you're asking for is to have KVM > *silently* drop data. Aside from the fact that such a change would break KVM's > ABI, silently ignoring data that userspace has explicitly requested be loaded for > a vCPU is incredibly dangerous.
Sorry if it came off that way - I fully understand and am resigned to the "you break it, you keep both halves" nature of what I had initially proposed and that it is not a generally tractable solution.
That being said, I genuinely appreciate your jump to action on this problem!
Thanks, Tyler
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