Subject: Re: [PATCH 12/14] KVM: arm/arm64: arch_timer: Assign the phys timer on VHE systems

From: Andre Przywara <[email-masked]>
Date: Wed, 20 Feb 2019 17:58:08 +0000

On Tue, 19 Feb 2019 13:43:49 +0100
Christoffer Dall <[email-masked]> wrote:

> On Mon, Feb 18, 2019 at 03:10:49PM +0000, André Przywara wrote:
> > On Thu, 24 Jan 2019 15:00:30 +0100
> > Christoffer Dall <[email-masked]> wrote:
> > 
> > Hi,
> >   
> > > VHE systems don't have to emulate the physical timer, we can simply
> > > assigne the EL1 physical timer directly to the VM as the host always
> > > uses the EL2 timers.
> > > 
> > > In order to minimize the amount of cruft, AArch32 gets definitions for
> > > the physical timer too, but is should be generally unused on this
> > > architecture.
> > > 
> > > Co-written with Marc Zyngier <[email-masked]>
> > > 
> > > Signed-off-by: Marc Zyngier <[email-masked]>
> > > Signed-off-by: Christoffer Dall <[email-masked]>
> > > ---
> > >  arch/arm/include/asm/kvm_hyp.h |   4 +
> > >  include/kvm/arm_arch_timer.h   |   6 +
> > >  virt/kvm/arm/arch_timer.c      | 206 ++++++++++++++++++++++++++-------
> > >  3 files changed, 171 insertions(+), 45 deletions(-)
> > > 
> > > diff --git a/arch/arm/include/asm/kvm_hyp.h b/arch/arm/include/asm/kvm_hyp.h
> > > index e93a0cac9add..87bcd18df8d5 100644
> > > --- a/arch/arm/include/asm/kvm_hyp.h
> > > +++ b/arch/arm/include/asm/kvm_hyp.h
> > > @@ -40,6 +40,7 @@
> > >  #define TTBR1		__ACCESS_CP15_64(1, c2)
> > >  #define VTTBR		__ACCESS_CP15_64(6, c2)
> > >  #define PAR		__ACCESS_CP15_64(0, c7)
> > > +#define CNTP_CVAL	__ACCESS_CP15_64(2, c14)
> > >  #define CNTV_CVAL	__ACCESS_CP15_64(3, c14)
> > >  #define CNTVOFF		__ACCESS_CP15_64(4, c14)
> > >  
> > > @@ -85,6 +86,7 @@
> > >  #define TID_PRIV	__ACCESS_CP15(c13, 0, c0, 4)
> > >  #define HTPIDR		__ACCESS_CP15(c13, 4, c0, 2)
> > >  #define CNTKCTL		__ACCESS_CP15(c14, 0, c1, 0)
> > > +#define CNTP_CTL	__ACCESS_CP15(c14, 0, c2, 1)
> > >  #define CNTV_CTL	__ACCESS_CP15(c14, 0, c3, 1)
> > >  #define CNTHCTL		__ACCESS_CP15(c14, 4, c1, 0)
> > >  
> > > @@ -94,6 +96,8 @@
> > >  #define read_sysreg_el0(r)		read_sysreg(r##_el0)
> > >  #define write_sysreg_el0(v, r)		write_sysreg(v, r##_el0)
> > >  
> > > +#define cntp_ctl_el0			CNTP_CTL
> > > +#define cntp_cval_el0			CNTP_CVAL
> > >  #define cntv_ctl_el0			CNTV_CTL
> > >  #define cntv_cval_el0			CNTV_CVAL
> > >  #define cntvoff_el2			CNTVOFF
> > > diff --git a/include/kvm/arm_arch_timer.h b/include/kvm/arm_arch_timer.h
> > > index d40fe57a2d0d..722e0481f310 100644
> > > --- a/include/kvm/arm_arch_timer.h
> > > +++ b/include/kvm/arm_arch_timer.h
> > > @@ -50,6 +50,10 @@ struct arch_timer_context {
> > >  
> > >  	/* Emulated Timer (may be unused) */
> > >  	struct hrtimer			hrtimer;
> > > +
> > > +	/* Duplicated state from arch_timer.c for convenience */
> > > +	u32				host_timer_irq;
> > > +	u32				host_timer_irq_flags;
> > >  };
> > >  
> > >  enum loaded_timer_state {
> > > @@ -107,6 +111,8 @@ bool kvm_arch_timer_get_input_level(int vintid);
> > >  #define vcpu_vtimer(v)	(&(v)->arch.timer_cpu.timers[TIMER_VTIMER])
> > >  #define vcpu_ptimer(v)	(&(v)->arch.timer_cpu.timers[TIMER_PTIMER])
> > >  
> > > +#define arch_timer_ctx_index(ctx)	((ctx) - vcpu_timer((ctx)->vcpu)->timers)
> > > +
> > >  u64 kvm_arm_timer_read_sysreg(struct kvm_vcpu *vcpu,
> > >  			      enum kvm_arch_timers tmr,
> > >  			      enum kvm_arch_timer_regs treg);
> > > diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c
> > > index 8b0eca5fbad1..eed8f48fbf9b 100644
> > > --- a/virt/kvm/arm/arch_timer.c
> > > +++ b/virt/kvm/arm/arch_timer.c
> > > @@ -35,7 +35,9 @@
> > >  
> > >  static struct timecounter *timecounter;
> > >  static unsigned int host_vtimer_irq;
> > > +static unsigned int host_ptimer_irq;
> > >  static u32 host_vtimer_irq_flags;
> > > +static u32 host_ptimer_irq_flags;
> > >  
> > >  static DEFINE_STATIC_KEY_FALSE(has_gic_active_state);
> > >  
> > > @@ -86,20 +88,24 @@ static void soft_timer_cancel(struct hrtimer *hrt)
> > >  static irqreturn_t kvm_arch_timer_handler(int irq, void *dev_id)
> > >  {
> > >  	struct kvm_vcpu *vcpu = *(struct kvm_vcpu **)dev_id;
> > > -	struct arch_timer_context *vtimer;
> > > +	struct arch_timer_context *ctx;
> > >  
> > >  	/*
> > >  	 * We may see a timer interrupt after vcpu_put() has been called which
> > >  	 * sets the CPU's vcpu pointer to NULL, because even though the timer
> > > -	 * has been disabled in vtimer_save_state(), the hardware interrupt
> > > +	 * has been disabled in timer_save_state(), the hardware interrupt
> > >  	 * signal may not have been retired from the interrupt controller yet.
> > >  	 */
> > >  	if (!vcpu)
> > >  		return IRQ_HANDLED;
> > >  
> > > -	vtimer = vcpu_vtimer(vcpu);
> > > -	if (kvm_timer_should_fire(vtimer))
> > > -		kvm_timer_update_irq(vcpu, true, vtimer);
> > > +	if (irq == host_vtimer_irq)
> > > +		ctx = vcpu_vtimer(vcpu);
> > > +	else
> > > +		ctx = vcpu_ptimer(vcpu);
> > > +
> > > +	if (kvm_timer_should_fire(ctx))
> > > +		kvm_timer_update_irq(vcpu, true, ctx);
> > >  
> > >  	if (userspace_irqchip(vcpu->kvm) &&
> > >  	    !static_branch_unlikely(&has_gic_active_state))
> > > @@ -208,13 +214,25 @@ static enum hrtimer_restart kvm_phys_timer_expire(struct hrtimer *hrt)
> > >  static bool kvm_timer_should_fire(struct arch_timer_context *timer_ctx)
> > >  {
> > >  	struct arch_timer_cpu *timer = vcpu_timer(timer_ctx->vcpu);
> > > +	enum kvm_arch_timers index = arch_timer_ctx_index(timer_ctx);
> > >  	u64 cval, now;
> > >  
> > >  	if (timer->loaded == TIMER_EL1_LOADED) {
> > > -		u32 cnt_ctl;
> > > +		u32 cnt_ctl = 0;
> > > +
> > > +		switch (index) {
> > > +		case TIMER_VTIMER:
> > > +			cnt_ctl = read_sysreg_el0(cntv_ctl);
> > > +			break;
> > > +		case TIMER_PTIMER:
> > > +			cnt_ctl = read_sysreg_el0(cntp_ctl);
> > > +			break;
> > > +		case NR_KVM_TIMERS:
> > > +			/* GCC is braindead */
> > > +			cnt_ctl = 0;
> > > +			break;
> > > +		}
> > >  
> > > -		/* Only the virtual timer can be loaded so far */
> > > -		cnt_ctl = read_sysreg_el0(cntv_ctl);
> > >  		return  (cnt_ctl & ARCH_TIMER_CTRL_ENABLE) &&
> > >  		        (cnt_ctl & ARCH_TIMER_CTRL_IT_STAT) &&
> > >  		       !(cnt_ctl & ARCH_TIMER_CTRL_IT_MASK);
> > > @@ -310,7 +328,7 @@ static void kvm_timer_update_state(struct kvm_vcpu *vcpu)
> > >  		return;
> > >  
> > >  	/*
> > > -	 * The vtimer virtual interrupt is a 'mapped' interrupt, meaning part
> > > +	 * If the timer virtual interrupt is a 'mapped' interrupt, part
> > >  	 * of its lifecycle is offloaded to the hardware, and we therefore may
> > >  	 * not have lowered the irq.level value before having to signal a new
> > >  	 * interrupt, but have to signal an interrupt every time the level is
> > > @@ -319,31 +337,55 @@ static void kvm_timer_update_state(struct kvm_vcpu *vcpu)
> > >  	level = kvm_timer_should_fire(vtimer);
> > >  	kvm_timer_update_irq(vcpu, level, vtimer);
> > >  
> > > +	if (has_vhe()) {  
> > 
> > Not really critical, but wouldn't it be cleaner to use "if
> > (host_ptimer_irq > 0)" here to check if we map the phys timer as well?
> > This is at least how we originally derive the decision to initialise
> > everything in kvm_timer_hyp_init() below. Applies to the other instances
> > of "if (has_vhe())" as well.
> > But I guess we use has_vhe() because it's a static key? In this case
> > would it be worth to define some cosmetic wrapper, to improve readability?
> >   
> > > +		level = kvm_timer_should_fire(ptimer);
> > > +		kvm_timer_update_irq(vcpu, level, ptimer);
> > > +
> > > +		return;
> > > +	}
> > > +
> > >  	phys_timer_emulate(vcpu);
> > >  
> > >  	if (kvm_timer_should_fire(ptimer) != ptimer->irq.level)
> > >  		kvm_timer_update_irq(vcpu, !ptimer->irq.level, ptimer);
> > >  }
> > >  
> > > -static void vtimer_save_state(struct kvm_vcpu *vcpu)
> > > +static void timer_save_state(struct arch_timer_context *ctx)
> > >  {
> > > -	struct arch_timer_cpu *timer = vcpu_timer(vcpu);
> > > -	struct arch_timer_context *vtimer = vcpu_vtimer(vcpu);
> > > +	struct arch_timer_cpu *timer = vcpu_timer(ctx->vcpu);
> > > +	enum kvm_arch_timers index = arch_timer_ctx_index(ctx);
> > >  	unsigned long flags;
> > >  
> > > +	if (!timer->enabled)
> > > +		return;
> > > +
> > >  	local_irq_save(flags);
> > >  
> > >  	if (timer->loaded == TIMER_NOT_LOADED)
> > >  		goto out;
> > >  
> > > -	if (timer->enabled) {
> > > -		vtimer->cnt_ctl = read_sysreg_el0(cntv_ctl);
> > > -		vtimer->cnt_cval = read_sysreg_el0(cntv_cval);
> > > -	}
> > > +	switch (index) {
> > > +	case TIMER_VTIMER:
> > > +		ctx->cnt_ctl = read_sysreg_el0(cntv_ctl);
> > > +		ctx->cnt_cval = read_sysreg_el0(cntv_cval);
> > >  
> > > -	/* Disable the virtual timer */
> > > -	write_sysreg_el0(0, cntv_ctl);
> > > -	isb();
> > > +		/* Disable the timer */
> > > +		write_sysreg_el0(0, cntv_ctl);
> > > +		isb();
> > > +
> > > +		break;
> > > +	case TIMER_PTIMER:
> > > +		ctx->cnt_ctl = read_sysreg_el0(cntp_ctl);
> > > +		ctx->cnt_cval = read_sysreg_el0(cntp_cval);
> > > +
> > > +		/* Disable the timer */
> > > +		write_sysreg_el0(0, cntp_ctl);
> > > +		isb();
> > > +
> > > +		break;
> > > +	case NR_KVM_TIMERS:
> > > +		break; /* GCC is braindead */
> > > +	}
> > >  
> > >  	timer->loaded = TIMER_NOT_LOADED;
> > >  out:
> > > @@ -382,21 +424,33 @@ static void kvm_timer_unblocking(struct kvm_vcpu *vcpu)
> > >  	soft_timer_cancel(&timer->bg_timer);
> > >  }
> > >  
> > > -static void vtimer_restore_state(struct kvm_vcpu *vcpu)
> > > +static void timer_restore_state(struct arch_timer_context *ctx)
> > >  {
> > > -	struct arch_timer_cpu *timer = vcpu_timer(vcpu);
> > > -	struct arch_timer_context *vtimer = vcpu_vtimer(vcpu);
> > > +	struct arch_timer_cpu *timer = vcpu_timer(ctx->vcpu);
> > > +	enum kvm_arch_timers index = arch_timer_ctx_index(ctx);
> > >  	unsigned long flags;
> > >  
> > > +	if (!timer->enabled)
> > > +		return;
> > > +
> > >  	local_irq_save(flags);
> > >  
> > >  	if (timer->loaded == TIMER_EL1_LOADED)
> > >  		goto out;
> > >  
> > > -	if (timer->enabled) {
> > > -		write_sysreg_el0(vtimer->cnt_cval, cntv_cval);
> > > +	switch (index) {
> > > +	case TIMER_VTIMER:
> > > +		write_sysreg_el0(ctx->cnt_cval, cntv_cval);
> > > +		isb();
> > > +		write_sysreg_el0(ctx->cnt_ctl, cntv_ctl);
> > > +		break;
> > > +	case TIMER_PTIMER:
> > > +		write_sysreg_el0(ctx->cnt_cval, cntp_cval);
> > >  		isb();
> > > -		write_sysreg_el0(vtimer->cnt_ctl, cntv_ctl);
> > > +		write_sysreg_el0(ctx->cnt_ctl, cntp_ctl);
> > > +		break;
> > > +	case NR_KVM_TIMERS:
> > > +		break; /* GCC is braindead */
> > >  	}
> > >  
> > >  	timer->loaded = TIMER_EL1_LOADED;
> > > @@ -419,23 +473,23 @@ static void set_cntvoff(u64 cntvoff)
> > >  	kvm_call_hyp(__kvm_timer_set_cntvoff, low, high);
> > >  }
> > >  
> > > -static inline void set_vtimer_irq_phys_active(struct kvm_vcpu *vcpu, bool active)
> > > +static inline void set_timer_irq_phys_active(struct arch_timer_context *ctx, bool active)
> > >  {
> > >  	int r;
> > > -	r = irq_set_irqchip_state(host_vtimer_irq, IRQCHIP_STATE_ACTIVE, active);
> > > +	r = irq_set_irqchip_state(ctx->host_timer_irq, IRQCHIP_STATE_ACTIVE, active);
> > >  	WARN_ON(r);
> > >  }
> > >  
> > > -static void kvm_timer_vcpu_load_gic(struct kvm_vcpu *vcpu)
> > > +static void kvm_timer_vcpu_load_gic(struct arch_timer_context *ctx)
> > >  {
> > > -	struct arch_timer_context *vtimer = vcpu_vtimer(vcpu);
> > > +	struct kvm_vcpu *vcpu = ctx->vcpu;
> > >  	bool phys_active;
> > >  
> > >  	if (irqchip_in_kernel(vcpu->kvm))
> > > -		phys_active = kvm_vgic_map_is_active(vcpu, vtimer->irq.irq);
> > > +		phys_active = kvm_vgic_map_is_active(vcpu, ctx->irq.irq);
> > >  	else
> > > -		phys_active = vtimer->irq.level;
> > > -	set_vtimer_irq_phys_active(vcpu, phys_active);
> > > +		phys_active = ctx->irq.level;
> > > +	set_timer_irq_phys_active(ctx, phys_active);
> > >  }
> > >  
> > >  static void kvm_timer_vcpu_load_nogic(struct kvm_vcpu *vcpu)
> > > @@ -467,14 +521,22 @@ void kvm_timer_vcpu_load(struct kvm_vcpu *vcpu)
> > >  	if (unlikely(!timer->enabled))
> > >  		return;
> > >  
> > > -	if (static_branch_likely(&has_gic_active_state))
> > > -		kvm_timer_vcpu_load_gic(vcpu);
> > > -	else
> > > +	if (static_branch_likely(&has_gic_active_state)) {
> > > +		kvm_timer_vcpu_load_gic(vtimer);
> > > +		if (has_vhe())
> > > +			kvm_timer_vcpu_load_gic(ptimer);
> > > +	} else {
> > >  		kvm_timer_vcpu_load_nogic(vcpu);
> > > +	}
> > >  
> > >  	set_cntvoff(vtimer->cntvoff);
> > >  
> > > -	vtimer_restore_state(vcpu);
> > > +	timer_restore_state(vtimer);
> > > +
> > > +	if (has_vhe()) {
> > > +		timer_restore_state(ptimer);
> > > +		return;
> > > +	}
> > >  
> > >  	/* Set the background timer for the physical timer emulation. */
> > >  	phys_timer_emulate(vcpu);
> > > @@ -506,12 +568,17 @@ bool kvm_timer_should_notify_user(struct kvm_vcpu *vcpu)
> > >  void kvm_timer_vcpu_put(struct kvm_vcpu *vcpu)
> > >  {
> > >  	struct arch_timer_cpu *timer = vcpu_timer(vcpu);
> > > +	struct arch_timer_context *vtimer = vcpu_vtimer(vcpu);
> > >  	struct arch_timer_context *ptimer = vcpu_ptimer(vcpu);
> > >  
> > >  	if (unlikely(!timer->enabled))
> > >  		return;
> > >  
> > > -	vtimer_save_state(vcpu);
> > > +	timer_save_state(vtimer);
> > > +	if (has_vhe()) {
> > > +		timer_save_state(ptimer);
> > > +		return;
> > > +	}
> > >  
> > >  	/*
> > >  	 * Cancel the physical timer emulation, because the only case where we
> > > @@ -534,8 +601,7 @@ void kvm_timer_vcpu_put(struct kvm_vcpu *vcpu)
> > >  	 * counter of non-VHE case. For VHE, the virtual counter uses a fixed
> > >  	 * virtual offset of zero, so no need to zero CNTVOFF_EL2 register.
> > >  	 */
> > > -	if (!has_vhe())
> > > -		set_cntvoff(0);
> > > +	set_cntvoff(0);
> > >  }
> > >  
> > >  /*
> > > @@ -550,7 +616,7 @@ static void unmask_vtimer_irq_user(struct kvm_vcpu *vcpu)
> > >  	if (!kvm_timer_should_fire(vtimer)) {
> > >  		kvm_timer_update_irq(vcpu, false, vtimer);
> > >  		if (static_branch_likely(&has_gic_active_state))
> > > -			set_vtimer_irq_phys_active(vcpu, false);
> > > +			set_timer_irq_phys_active(vtimer, false);
> > >  		else
> > >  			enable_percpu_irq(host_vtimer_irq, host_vtimer_irq_flags);
> > >  	}
> > > @@ -625,7 +691,12 @@ void kvm_timer_vcpu_init(struct kvm_vcpu *vcpu)
> > >  	ptimer->hrtimer.function = kvm_phys_timer_expire;
> > >  
> > >  	vtimer->irq.irq = default_vtimer_irq.irq;
> > > +	vtimer->host_timer_irq = host_vtimer_irq;
> > > +	vtimer->host_timer_irq_flags = host_vtimer_irq_flags;
> > > +
> > >  	ptimer->irq.irq = default_ptimer_irq.irq;
> > > +	ptimer->host_timer_irq = host_ptimer_irq;
> > > +	ptimer->host_timer_irq_flags = host_ptimer_irq_flags;
> > >  
> > >  	vtimer->vcpu = vcpu;
> > >  	ptimer->vcpu = vcpu;
> > > @@ -634,6 +705,7 @@ void kvm_timer_vcpu_init(struct kvm_vcpu *vcpu)
> > >  static void kvm_timer_init_interrupt(void *info)
> > >  {
> > >  	enable_percpu_irq(host_vtimer_irq, host_vtimer_irq_flags);
> > > +	enable_percpu_irq(host_ptimer_irq, host_ptimer_irq_flags);  
> > 
> > Shouldn't we only enable host_ptimer_irq() if we actually pass this on
> > here? So either guarded by has_vhe() or (host_ptimer_irq > 0)?
> > Otherwise we would enable IRQ 0?
> >   
> 
> I think the right fix is to raise an error if a VHE system doesn't give
> us a valid physical irq number during init, and then leave the checks
> for has_vhe() here.

That sounds like a good compromise to me. I just want to avoid the casual
reader to be puzzled about the dependency between "phys timer passed on"
and VHE. Comments would probably do as well.

Thanks!
Andre.

_______________________________________________
linux-arm-kernel mailing list
[email-masked]
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel