Subject: [PATCH v3 6/6] arm/arm64: KVM: Require in-kernel vgic for the arch timers

From: [email-masked] (Christoffer Dall)
Date: Mon, 15 Dec 2014 11:50:10 +0100

On Mon, Dec 15, 2014 at 10:39:23AM +0000, Marc Zyngier wrote:
> On 15/12/14 10:20, Christoffer Dall wrote:
> > It is curently possible to run a VM with architected timers support
> > without creating an in-kernel VGIC, which will result in interrupts from
> > the virtual timer going nowhere.
> > 
> > To address this issue, move the architected timers initialization to the
> > time when we run a VCPU for the first time, and then only initialize
> > (and enable) the architected timers if we have a properly created and
> > initialized in-kernel VGIC.
> > 
> > When injecting interrupts from the virtual timer to the vgic, the
> > current setup should ensure that this never calls an on-demand init of
> > the VGIC, which is the only call path that could return an error from
> > kvm_vgic_inject_irq(), so capture the return value and raise a warning
> > if there's an error there.
> > 
> > We also change the kvm_timer_init() function from returning an int to be
> > a void function, since the function always succeeds.
> > 
> > Signed-off-by: Christoffer Dall <[email-masked]>
> > ---
> > Changes [v2 -> v3]:
> >  - Split kvm_timer_init into kvm_timer_init and kvm_timer_enable
> >    and initialize the cntvoff in kvm_timer_init and only actually enable
> >    the timer if there is an in-kernel vgic.
> >  - Added comment about race from multiple VCPUs.
> >  - Support compiling on 32-bit ARM wihtout vgic/arch-timers config
> >    option.
> > 
> >  arch/arm/kvm/arm.c           | 13 +++++++++++--
> >  include/kvm/arm_arch_timer.h | 10 ++++------
> >  virt/kvm/arm/arch_timer.c    | 30 ++++++++++++++++++++++--------
> >  3 files changed, 37 insertions(+), 16 deletions(-)
> > 
> > diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
> > index d4da244..8cadfec 100644
> > --- a/arch/arm/kvm/arm.c
> > +++ b/arch/arm/kvm/arm.c
> > @@ -424,6 +424,7 @@ static void update_vttbr(struct kvm *kvm)
> >  
> >  static int kvm_vcpu_first_run_init(struct kvm_vcpu *vcpu)
> >  {
> > +	struct kvm *kvm = vcpu->kvm;
> >  	int ret;
> >  
> >  	if (likely(vcpu->arch.has_run_once))
> > @@ -435,12 +436,20 @@ static int kvm_vcpu_first_run_init(struct kvm_vcpu *vcpu)
> >  	 * Map the VGIC hardware resources before running a vcpu the first
> >  	 * time on this VM.
> >  	 */
> > -	if (unlikely(!vgic_ready(vcpu->kvm))) {
> > -		ret = kvm_vgic_map_resources(vcpu->kvm);
> > +	if (unlikely(!vgic_ready(kvm))) {
> > +		ret = kvm_vgic_map_resources(kvm);
> >  		if (ret)
> >  			return ret;
> >  	}
> >  
> > +	/*
> > +	 * Enable the arch timers only if we have an in-kernel VGIC
> > +	 * and it has been properly initialized, since we cannot handle
> > +	 * interrupts from the virtual timer with a userspace gic.
> > +	 */
> > +	if (irqchip_in_kernel(kvm) && vgic_initialized(kvm))
> > +		kvm_timer_enable(kvm);
> > +
> >  	return 0;
> >  }
> >  
> > diff --git a/include/kvm/arm_arch_timer.h b/include/kvm/arm_arch_timer.h
> > index ad9db60..b3f45a5 100644
> > --- a/include/kvm/arm_arch_timer.h
> > +++ b/include/kvm/arm_arch_timer.h
> > @@ -60,7 +60,8 @@ struct arch_timer_cpu {
> >  
> >  #ifdef CONFIG_KVM_ARM_TIMER
> >  int kvm_timer_hyp_init(void);
> > -int kvm_timer_init(struct kvm *kvm);
> > +void kvm_timer_enable(struct kvm *kvm);
> > +void kvm_timer_init(struct kvm *kvm);
> >  void kvm_timer_vcpu_reset(struct kvm_vcpu *vcpu,
> >  			  const struct kvm_irq_level *irq);
> >  void kvm_timer_vcpu_init(struct kvm_vcpu *vcpu);
> > @@ -77,11 +78,8 @@ static inline int kvm_timer_hyp_init(void)
> >  	return 0;
> >  };
> >  
> > -static inline int kvm_timer_init(struct kvm *kvm)
> > -{
> > -	return 0;
> > -}
> > -
> > +static inline void kvm_timer_enable(struct kvm *kvm) {}
> > +static inline void kvm_timer_init(struct kvm *kvm) {}
> >  static inline void kvm_timer_vcpu_reset(struct kvm_vcpu *vcpu,
> >  					const struct kvm_irq_level *irq) {}
> >  static inline void kvm_timer_vcpu_init(struct kvm_vcpu *vcpu) {}
> > diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c
> > index 22fa819..1c0772b 100644
> > --- a/virt/kvm/arm/arch_timer.c
> > +++ b/virt/kvm/arm/arch_timer.c
> > @@ -61,12 +61,14 @@ static void timer_disarm(struct arch_timer_cpu *timer)
> >  
> >  static void kvm_timer_inject_irq(struct kvm_vcpu *vcpu)
> >  {
> > +	int ret;
> >  	struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
> >  
> >  	timer->cntv_ctl |= ARCH_TIMER_CTRL_IT_MASK;
> > -	kvm_vgic_inject_irq(vcpu->kvm, vcpu->vcpu_id,
> > -			    timer->irq->irq,
> > -			    timer->irq->level);
> > +	ret = kvm_vgic_inject_irq(vcpu->kvm, vcpu->vcpu_id,
> > +				  timer->irq->irq,
> > +				  timer->irq->level);
> > +	WARN_ON(ret);
> >  }
> >  
> >  static irqreturn_t kvm_arch_timer_handler(int irq, void *dev_id)
> > @@ -307,12 +309,24 @@ void kvm_timer_vcpu_terminate(struct kvm_vcpu *vcpu)
> >  	timer_disarm(timer);
> >  }
> >  
> > -int kvm_timer_init(struct kvm *kvm)
> > +void kvm_timer_enable(struct kvm *kvm)
> >  {
> > -	if (timecounter && wqueue) {
> > -		kvm->arch.timer.cntvoff = kvm_phys_timer_read();
> > +	if (kvm->arch.timer.enabled)
> > +		return;
> > +
> > +	/*
> > +	 * There is a potential race here between VCPUs starting for the first
> > +	 * time, which may be enabling the timer multiple times.  That doesn't
> > +	 * hurt though, because we're just setting a variable to the same
> > +	 * variable that it already was.  The important thing is that all
> > +	 * VCPUs have the enabled variable set, before entering the guest, if
> > +	 * the arch timers are enabled.
> > +	 */
> > +	if (timecounter && wqueue)
> >  		kvm->arch.timer.enabled = 1;
> > -	}
> > +}
> 
> This is particularly interesting, as this paves the way for per-vcpu
> enable bits, meaning that we won't have to extract the enable bit from
> struct kvm while doing a world switch. Clearly a fight for another day
> though.
> 

I didn't think of that, but sounds good.

> >  
> > -	return 0;
> > +void kvm_timer_init(struct kvm *kvm)
> > +{
> > +	kvm->arch.timer.cntvoff = kvm_phys_timer_read();
> >  }
> > 
> 
> Looks good to me.
> 
> Reviewed-by: Marc Zyngier <[email-masked]>
> 
Thanks, I'll go ahead and get these series merged then.

-Christoffer