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

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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.

   - 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

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