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References: <20210709043713.887098-1-senozhatsky@chromium.org>
 <20210709043713.887098-5-senozhatsky@chromium.org> <874kcz33g5.wl-maz@kernel.org>
In-Reply-To: <874kcz33g5.wl-maz@kernel.org>
From:   Joel Fernandes <joelaf@google.com>
Date:   Tue, 20 Jul 2021 14:44:53 -0400
Message-ID: <CAJWu+oqCyj3H0=1KNo3c+crdcktYinFoTQJ5jHgU8gjeF4d2yA@mail.gmail.com>
Subject: Re: [PATCHv2 4/4] arm64: add host pv-vcpu-state support
To:     Marc Zyngier <maz@kernel.org>
Cc:     Sergey Senozhatsky <senozhatsky@chromium.org>,
        Will Deacon <will@kernel.org>,
        Suleiman Souhlal <suleiman@google.com>,
        linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu,
        linux-kernel@vger.kernel.org,
        virtualization@lists.linux-foundation.org
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On Mon, Jul 12, 2021 at 12:24 PM Marc Zyngier <maz@kernel.org> wrote:
>
[...]
> > +}
> > +
> > +static inline bool
> > +kvm_arm_is_vcpu_state_enabled(struct kvm_vcpu_arch *vcpu_arch)
> > +{
> > +     return (vcpu_arch->vcpu_state.base != GPA_INVALID);
> > +}
> > +
> > +void kvm_update_vcpu_preempted(struct kvm_vcpu *vcpu, bool preempted);
> > +
> >  void kvm_set_sei_esr(struct kvm_vcpu *vcpu, u64 syndrome);
> >
> >  struct kvm_vcpu *kvm_mpidr_to_vcpu(struct kvm *kvm, unsigned long mpidr);
> > diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
> > index 989bb5dad2c8..2a3ee82c6d90 100644
> > --- a/arch/arm64/kvm/Makefile
> > +++ b/arch/arm64/kvm/Makefile
> > @@ -12,7 +12,8 @@ obj-$(CONFIG_KVM) += hyp/
> >
> >  kvm-y := $(KVM)/kvm_main.o $(KVM)/coalesced_mmio.o $(KVM)/eventfd.o \
> >        $(KVM)/vfio.o $(KVM)/irqchip.o $(KVM)/binary_stats.o \
> > -      arm.o mmu.o mmio.o psci.o perf.o hypercalls.o pvtime.o \
> > +      arm.o mmu.o mmio.o psci.o perf.o hypercalls.o \
> > +      pvtime.o pv-vcpu-state.o \
> >        inject_fault.o va_layout.o handle_exit.o \
> >        guest.o debug.o reset.o sys_regs.o \
> >        vgic-sys-reg-v3.o fpsimd.o pmu.o \
> > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> > index e9a2b8f27792..43e995c9fddb 100644
> > --- a/arch/arm64/kvm/arm.c
> > +++ b/arch/arm64/kvm/arm.c
> > @@ -332,6 +332,7 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
> >       kvm_arm_reset_debug_ptr(vcpu);
> >
> >       kvm_arm_pvtime_vcpu_init(&vcpu->arch);
> > +     kvm_arm_vcpu_state_init(&vcpu->arch);
> >
> >       vcpu->arch.hw_mmu = &vcpu->kvm->arch.mmu;
> >
> > @@ -429,10 +430,12 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
> >       if (vcpu_has_ptrauth(vcpu))
> >               vcpu_ptrauth_disable(vcpu);
> >       kvm_arch_vcpu_load_debug_state_flags(vcpu);
> > +     kvm_update_vcpu_preempted(vcpu, false);
> >  }
> >
> >  void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
> >  {
> > +     kvm_update_vcpu_preempted(vcpu, true);
>
> This doesn't look right. With this, you are now telling the guest that
> a vcpu that is blocked on WFI is preempted. This really isn't the
> case, as it has voluntarily entered a low-power mode while waiting for
> an interrupt. Indeed, the vcpu isn't running. A physical CPU wouldn't
> be running either.

Can that be cured by just checking vcpu->preempted before calling
kvm_update_vcpu_preempted() ?

- Joel