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Message-ID: <867f5e9j4y.fsf@arm.com>
Date: Sun, 29 Jan 2017 11:54:05 +0000
From: Marc Zyngier <marc.zyngier@....com>
To: Jintack Lim <jintack@...columbia.edu>
Cc: <pbonzini@...hat.com>, <rkrcmar@...hat.com>,
<christoffer.dall@...aro.org>, <linux@...linux.org.uk>,
<catalin.marinas@....com>, <will.deacon@....com>,
<andre.przywara@....com>, <kvm@...r.kernel.org>,
<linux-arm-kernel@...ts.infradead.org>,
<kvmarm@...ts.cs.columbia.edu>, <linux-kernel@...r.kernel.org>
Subject: Re: [RFC v2 02/10] KVM: arm/arm64: Move cntvoff to each timer context
On Fri, Jan 27 2017 at 01:04:52 AM, Jintack Lim <jintack@...columbia.edu> wrote:
> Make cntvoff per each timer context. This is helpful to abstract kvm
> timer functions to work with timer context without considering timer
> types (e.g. physical timer or virtual timer).
>
> This also would pave the way for ever doing adjustments of the cntvoff
> on a per-CPU basis if that should ever make sense.
>
> Signed-off-by: Jintack Lim <jintack@...columbia.edu>
> ---
> arch/arm/include/asm/kvm_host.h | 6 +++---
> arch/arm64/include/asm/kvm_host.h | 4 ++--
> include/kvm/arm_arch_timer.h | 8 +++-----
> virt/kvm/arm/arch_timer.c | 26 ++++++++++++++++++++------
> virt/kvm/arm/hyp/timer-sr.c | 3 +--
> 5 files changed, 29 insertions(+), 18 deletions(-)
>
> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> index d5423ab..f5456a9 100644
> --- a/arch/arm/include/asm/kvm_host.h
> +++ b/arch/arm/include/asm/kvm_host.h
> @@ -60,9 +60,6 @@ struct kvm_arch {
> /* The last vcpu id that ran on each physical CPU */
> int __percpu *last_vcpu_ran;
>
> - /* Timer */
> - struct arch_timer_kvm timer;
> -
> /*
> * Anything that is not used directly from assembly code goes
> * here.
> @@ -75,6 +72,9 @@ struct kvm_arch {
> /* Stage-2 page table */
> pgd_t *pgd;
>
> + /* A lock to synchronize cntvoff among all vtimer context of vcpus */
> + spinlock_t cntvoff_lock;
Is there any condition where we need this to be a spinlock? I would have
thought that a mutex should have been enough, as this should only be
updated on migration or initialization. Not that it matters much in this
case, but I wondered if there is something I'm missing.
> +
> /* Interrupt controller */
> struct vgic_dist vgic;
> int max_vcpus;
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index e505038..23749a8 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -71,8 +71,8 @@ struct kvm_arch {
> /* Interrupt controller */
> struct vgic_dist vgic;
>
> - /* Timer */
> - struct arch_timer_kvm timer;
> + /* A lock to synchronize cntvoff among all vtimer context of vcpus */
> + spinlock_t cntvoff_lock;
> };
>
> #define KVM_NR_MEM_OBJS 40
> diff --git a/include/kvm/arm_arch_timer.h b/include/kvm/arm_arch_timer.h
> index daad3c1..1b9c988 100644
> --- a/include/kvm/arm_arch_timer.h
> +++ b/include/kvm/arm_arch_timer.h
> @@ -23,11 +23,6 @@
> #include <linux/hrtimer.h>
> #include <linux/workqueue.h>
>
> -struct arch_timer_kvm {
> - /* Virtual offset */
> - u64 cntvoff;
> -};
> -
> struct arch_timer_context {
> /* Registers: control register, timer value */
> u32 cnt_ctl;
> @@ -38,6 +33,9 @@ struct arch_timer_context {
>
> /* Active IRQ state caching */
> bool active_cleared_last;
> +
> + /* Virtual offset */
> + u64 cntvoff;
> };
>
> struct arch_timer_cpu {
> diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c
> index 6740efa..fa4c042 100644
> --- a/virt/kvm/arm/arch_timer.c
> +++ b/virt/kvm/arm/arch_timer.c
> @@ -101,9 +101,10 @@ static void kvm_timer_inject_irq_work(struct work_struct *work)
> static u64 kvm_timer_compute_delta(struct kvm_vcpu *vcpu)
> {
> u64 cval, now;
> + struct arch_timer_context *vtimer = vcpu_vtimer(vcpu);
>
> - cval = vcpu_vtimer(vcpu)->cnt_cval;
> - now = kvm_phys_timer_read() - vcpu->kvm->arch.timer.cntvoff;
> + cval = vtimer->cnt_cval;
> + now = kvm_phys_timer_read() - vtimer->cntvoff;
>
> if (now < cval) {
> u64 ns;
> @@ -159,7 +160,7 @@ bool kvm_timer_should_fire(struct kvm_vcpu *vcpu)
> return false;
>
> cval = vtimer->cnt_cval;
> - now = kvm_phys_timer_read() - vcpu->kvm->arch.timer.cntvoff;
> + now = kvm_phys_timer_read() - vtimer->cntvoff;
>
> return cval <= now;
> }
> @@ -353,10 +354,23 @@ int kvm_timer_vcpu_reset(struct kvm_vcpu *vcpu,
> return 0;
> }
>
> +/* Make the updates of cntvoff for all vtimer contexts atomic */
> +static void update_vtimer_cntvoff(struct kvm_vcpu *vcpu, u64 cntvoff)
Arguably, this acts on the VM itself and not a single vcpu. maybe you
should consider passing the struct kvm pointer to reflect this.
> +{
> + int i;
> +
> + spin_lock(&vcpu->kvm->arch.cntvoff_lock);
> + kvm_for_each_vcpu(i, vcpu, vcpu->kvm)
> + vcpu_vtimer(vcpu)->cntvoff = cntvoff;
> + spin_unlock(&vcpu->kvm->arch.cntvoff_lock);
> +}
> +
> void kvm_timer_vcpu_init(struct kvm_vcpu *vcpu)
> {
> struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
>
> + update_vtimer_cntvoff(vcpu, kvm_phys_timer_read());
Maybe a comment indicating that we recompute CNTVOFF for all vcpus would
be welcome (this is not a change in semantics, but it was never obvious
in the existing code).
> +
> INIT_WORK(&timer->expired, kvm_timer_inject_irq_work);
> hrtimer_init(&timer->timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
> timer->timer.function = kvm_timer_expire;
> @@ -376,7 +390,7 @@ int kvm_arm_timer_set_reg(struct kvm_vcpu *vcpu, u64 regid, u64 value)
> vtimer->cnt_ctl = value;
> break;
> case KVM_REG_ARM_TIMER_CNT:
> - vcpu->kvm->arch.timer.cntvoff = kvm_phys_timer_read() - value;
> + update_vtimer_cntvoff(vcpu, kvm_phys_timer_read() - value);
> break;
> case KVM_REG_ARM_TIMER_CVAL:
> vtimer->cnt_cval = value;
> @@ -397,7 +411,7 @@ u64 kvm_arm_timer_get_reg(struct kvm_vcpu *vcpu, u64 regid)
> case KVM_REG_ARM_TIMER_CTL:
> return vtimer->cnt_ctl;
> case KVM_REG_ARM_TIMER_CNT:
> - return kvm_phys_timer_read() - vcpu->kvm->arch.timer.cntvoff;
> + return kvm_phys_timer_read() - vtimer->cntvoff;
> case KVM_REG_ARM_TIMER_CVAL:
> return vtimer->cnt_cval;
> }
> @@ -511,7 +525,7 @@ int kvm_timer_enable(struct kvm_vcpu *vcpu)
>
> void kvm_timer_init(struct kvm *kvm)
> {
> - kvm->arch.timer.cntvoff = kvm_phys_timer_read();
> + spin_lock_init(&kvm->arch.cntvoff_lock);
> }
>
> /*
> diff --git a/virt/kvm/arm/hyp/timer-sr.c b/virt/kvm/arm/hyp/timer-sr.c
> index 0cf0895..4734915 100644
> --- a/virt/kvm/arm/hyp/timer-sr.c
> +++ b/virt/kvm/arm/hyp/timer-sr.c
> @@ -53,7 +53,6 @@ void __hyp_text __timer_save_state(struct kvm_vcpu *vcpu)
>
> void __hyp_text __timer_restore_state(struct kvm_vcpu *vcpu)
> {
> - struct kvm *kvm = kern_hyp_va(vcpu->kvm);
> struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
> struct arch_timer_context *vtimer = vcpu_vtimer(vcpu);
> u64 val;
> @@ -71,7 +70,7 @@ void __hyp_text __timer_restore_state(struct kvm_vcpu *vcpu)
> }
>
> if (timer->enabled) {
> - write_sysreg(kvm->arch.timer.cntvoff, cntvoff_el2);
> + write_sysreg(vtimer->cntvoff, cntvoff_el2);
> write_sysreg_el0(vtimer->cnt_cval, cntv_cval);
> isb();
> write_sysreg_el0(vtimer->cnt_ctl, cntv_ctl);
Thanks,
M.
--
Jazz is not dead. It just smells funny.
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