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Message-ID: <CAHyh4xiL18DPsR52FtLhafRWuycb5zA6MRL-SSSCRX96Ce-6ug@mail.gmail.com>
Date: Mon, 30 Jan 2017 12:58:11 -0500
From: Jintack Lim <jintack@...columbia.edu>
To: Marc Zyngier <marc.zyngier@....com>
Cc: Paolo Bonzini <pbonzini@...hat.com>,
Radim Krčmář <rkrcmar@...hat.com>,
Christoffer Dall <christoffer.dall@...aro.org>,
linux@...linux.org.uk, Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will.deacon@....com>,
Andre Przywara <andre.przywara@....com>,
KVM General <kvm@...r.kernel.org>,
arm-mail-list <linux-arm-kernel@...ts.infradead.org>,
kvmarm@...ts.cs.columbia.edu,
lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC v2 02/10] KVM: arm/arm64: Move cntvoff to each timer context
On Sun, Jan 29, 2017 at 6:54 AM, Marc Zyngier <marc.zyngier@....com> wrote:
> 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.
>
Yes, that would be better.
>> +{
>> + 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).
I'll add a comment. In fact, I was told to make cntvoff synchronized
across all the vcpus, but I'm afraid that I understand why. Could you
explain me where this constraint comes from?
>
>> +
>> 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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