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Date: Wed, 21 Jul 2021 19:38:40 +0900 From: Sergey Senozhatsky <senozhatsky@...omium.org> To: Marc Zyngier <maz@...nel.org> Cc: Joel Fernandes <joelaf@...gle.com>, Sergey Senozhatsky <senozhatsky@...omium.org>, Will Deacon <will@...nel.org>, Suleiman Souhlal <suleiman@...gle.com>, linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu, linux-kernel@...r.kernel.org, virtualization@...ts.linux-foundation.org Subject: Re: [PATCHv2 4/4] arm64: add host pv-vcpu-state support On (21/07/21 09:40), Marc Zyngier wrote: > > > > Can that be cured by just checking vcpu->preempted before calling > > kvm_update_vcpu_preempted() ? > > It isn't obvious to me that this is the right thing to do. > vcpu->preempted is always updated on sched-out from the preempt > notifier if the vcpu was on the run-queue, so my guess is that it will > always be set when switching to another task. > > What you probably want is to check whether the vcpu is blocked by > introspecting the wait-queue with: > > scuwait_active(kvm_arch_vcpu_get_wait(vcpu) > > which will tell you whether you are blocking or not. We are already > using a similar construct for arming a background timer in this case. Can we examine if vcpu->run->exit_reason == WFE/WFI and avoid setting preempted state if so?
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