Re: [PATCH v2 00/43] KVM: Halt-polling and x86 APICv overhaul

[Christian Borntraeger]

Am 26.10.21 um 16:48 schrieb Sean Christopherson:
> On Tue, Oct 26, 2021, Christian Borntraeger wrote:
> > Am 09.10.21 um 04:11 schrieb Sean Christopherson:
> > > This is basically two series smushed into one.  The first "half" aims
> > > to differentiate between "halt" and a more generic "block", where "halt"
> > > aligns with x86's HLT instruction, the halt-polling mechanisms, and
> > > associated stats, and "block" means any guest action that causes the vCPU
> > > to block/wait.
> > >
> > > The second "half" overhauls x86's APIC virtualization code (Posted
> > > Interrupts on Intel VMX, AVIC on AMD SVM) to do their updates in response
> > > to vCPU (un)blocking in the vcpu_load/put() paths, keying off of the
> > > vCPU's rcuwait status to determine when a blocking vCPU is being put and
> > > reloaded.  This idea comes from arm64's kvm_timer_vcpu_put(), which I
> > > stumbled across when diving into the history of arm64's (un)blocking hooks.
> > >
> > > The x86 APICv overhaul allows for killing off several sets of hooks in
> > > common KVM and in x86 KVM (to the vendor code).  Moving everything to
> > > vcpu_put/load() also realizes nice cleanups, especially for the Posted
> > > Interrupt code, which required some impressive mental gymnastics to
> > > understand how vCPU task migration interacted with vCPU blocking.
> > >
> > > Non-x86 folks, sorry for the noise.  I'm hoping the common parts can get
> > > applied without much fuss so that future versions can be x86-only.
> > >
> > > v2:
> > >    - Collect reviews. [Christian, David]
> > >    - Add patch to move arm64 WFI functionality out of hooks. [Marc]
> > >    - Add RISC-V to the fun.
> > >    - Add all the APICv fun.
> >
> > Have we actually followed up on the regression regarding halt_poll_ns=0 no longer disabling
> > polling for running systems?
>
> No, I have that conversation flagged but haven't gotten back to it.  I still like
> the idea of special casing halt_poll_ns=0 to override the capability.  I can send
> a proper patch for that unless there's a different/better idea?

I think I would prefer a variant that uses the halt_poll_ns value AS IS for all
guests that have not opted in the per guest feature.
And then MAYBE have 0 as a special case to disable that also for the opted in
VMs.