Re: Re: [RFC PATCH v2 1/7] KVM: x86: Avoid silent kvm-clock activation failures

[Takahiro Itazuri <itazur@amazon.com>]

On Thu, 5 Mar 2026 09:50:30 -0800, Sean Christopherson wrote:
> On Thu, Feb 26, 2026, Takahiro Itazuri wrote:
> > kvm_write_system_time() previously ignored the return value of
> > kvm_gpc_activate().  As a result, kvm-clock activation could fail
> > silently, making debugging harder.
> > 
> > Propagate the return value so that the MSR write fail properly instead
> > of continuing silently.
> 
> Hrm.  For better or worse, KVM's ABI when it comes to PV stuff is to silently
> ignore failures.  I 100% agree it makes debugging painful, but it's unfortunately
> also "safer" in many cases, e.g. often results in degraded behavior versus flat
> out crashing the guest.
> 
> The other wrinkle is that success isn't actually guaranteed, because the actual
> writes don't happen until KVM_RUN via kvm_guest_time_update(), i.e. only failing
> in _some_ cases creates a weird ABI.
> 
> And most importantly, this would be a breaking change in guest- and user-visible
> behavior.  So while I agree silently failing is ugly, all things considered I
> think it's the least awful choice here :-/

Fair point.  I'll drop this change in the next version since I spotted a
compile error in another patch and I need to resend anyway.