Re: [RFC PATCH 12/28] KVM: arm64: Support timers in realm RECs

[Steven Price]

On 18/03/2024 11:28, Ganapatrao Kulkarni wrote:
> 
> 
> On 27-01-2023 04:59 pm, Steven Price wrote:
>> The RMM keeps track of the timer while the realm REC is running, but on
>> exit to the normal world KVM is responsible for handling the timers.
>>
>> Signed-off-by: Steven Price <steven.price@xxxxxxx>
>> ---
>>   arch/arm64/kvm/arch_timer.c  | 53 ++++++++++++++++++++++++++++++++----
>>   include/kvm/arm_arch_timer.h |  2 ++
>>   2 files changed, 49 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/arm64/kvm/arch_timer.c b/arch/arm64/kvm/arch_timer.c
>> index bb24a76b4224..d4af9ee58550 100644
>> --- a/arch/arm64/kvm/arch_timer.c
>> +++ b/arch/arm64/kvm/arch_timer.c
>> @@ -130,6 +130,11 @@ static void timer_set_offset(struct
>> arch_timer_context *ctxt, u64 offset)
>>   {
>>       struct kvm_vcpu *vcpu = ctxt->vcpu;
>>   +    if (kvm_is_realm(vcpu->kvm)) {
>> +        WARN_ON(offset);
>> +        return;
>> +    }
>> +
>>       switch(arch_timer_ctx_index(ctxt)) {
>>       case TIMER_VTIMER:
>>           __vcpu_sys_reg(vcpu, CNTVOFF_EL2) = offset;
>> @@ -411,6 +416,21 @@ static void kvm_timer_update_irq(struct kvm_vcpu
>> *vcpu, bool new_level,
>>       }
>>   }
>>   +void kvm_realm_timers_update(struct kvm_vcpu *vcpu)
>> +{
>> +    struct arch_timer_cpu *arch_timer = &vcpu->arch.timer_cpu;
>> +    int i;
>> +
>> +    for (i = 0; i < NR_KVM_TIMERS; i++) {
> 
> Do we required to check for all timers, is realm/rmm uses hyp timers?

Good point, the realm guest can't use the hyp timers, so this should be
NR_KVM_EL0_TIMERS. The hyp timers are used by the host to interrupt the
guest execution. I think this code was written before NV support added
the extra timers.

>> +        struct arch_timer_context *timer = &arch_timer->timers[i];
>> +        bool status = timer_get_ctl(timer) & ARCH_TIMER_CTRL_IT_STAT;
>> +        bool level = kvm_timer_irq_can_fire(timer) && status;
>> +
>> +        if (level != timer->irq.level)
>> +            kvm_timer_update_irq(vcpu, level, timer);
>> +    }
>> +}
>> +
>>   /* Only called for a fully emulated timer */
>>   static void timer_emulate(struct arch_timer_context *ctx)
>>   {
>> @@ -621,6 +641,11 @@ void kvm_timer_vcpu_load(struct kvm_vcpu *vcpu)
>>       if (unlikely(!timer->enabled))
>>           return;
>>   +    kvm_timer_unblocking(vcpu);
>> +
>> +    if (vcpu_is_rec(vcpu))
>> +        return;
>> +
> 
> For realm, timer->enabled is not set, load returns before this check.

True, this can be simplified. Thanks.

Steve

>>       get_timer_map(vcpu, &map);
>>         if (static_branch_likely(&has_gic_active_state)) {
>> @@ -633,8 +658,6 @@ void kvm_timer_vcpu_load(struct kvm_vcpu *vcpu)
>>         set_cntvoff(timer_get_offset(map.direct_vtimer));
>>   -    kvm_timer_unblocking(vcpu);
>> -
>>       timer_restore_state(map.direct_vtimer);
>>       if (map.direct_ptimer)
>>           timer_restore_state(map.direct_ptimer);
>> @@ -668,6 +691,9 @@ void kvm_timer_vcpu_put(struct kvm_vcpu *vcpu)
>>       if (unlikely(!timer->enabled))
>>           return;
>>   +    if (vcpu_is_rec(vcpu))
>> +        goto out;
>> +
>>       get_timer_map(vcpu, &map);
>>         timer_save_state(map.direct_vtimer);
>> @@ -686,9 +712,6 @@ void kvm_timer_vcpu_put(struct kvm_vcpu *vcpu)
>>       if (map.emul_ptimer)
>>           soft_timer_cancel(&map.emul_ptimer->hrtimer);
>>   -    if (kvm_vcpu_is_blocking(vcpu))
>> -        kvm_timer_blocking(vcpu);
>> -
>>       /*
>>        * The kernel may decide to run userspace after calling
>> vcpu_put, so
>>        * we reset cntvoff to 0 to ensure a consistent read between user
>> @@ -697,6 +720,11 @@ void kvm_timer_vcpu_put(struct kvm_vcpu *vcpu)
>>        * virtual offset of zero, so no need to zero CNTVOFF_EL2 register.
>>        */
>>       set_cntvoff(0);
>> +
>> +out:
>> +    if (kvm_vcpu_is_blocking(vcpu))
>> +        kvm_timer_blocking(vcpu);
>> +
>>   }
>>     /*
>> @@ -785,12 +813,18 @@ void kvm_timer_vcpu_init(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);
>> +    u64 cntvoff;
>>         vtimer->vcpu = vcpu;
>>       ptimer->vcpu = vcpu;
>>   +    if (kvm_is_realm(vcpu->kvm))
>> +        cntvoff = 0;
>> +    else
>> +        cntvoff = kvm_phys_timer_read();
>> +
>>       /* Synchronize cntvoff across all vtimers of a VM. */
>> -    update_vtimer_cntvoff(vcpu, kvm_phys_timer_read());
>> +    update_vtimer_cntvoff(vcpu, cntvoff);
>>       timer_set_offset(ptimer, 0);
>>         hrtimer_init(&timer->bg_timer, CLOCK_MONOTONIC,
>> HRTIMER_MODE_ABS_HARD);
>> @@ -1265,6 +1299,13 @@ int kvm_timer_enable(struct kvm_vcpu *vcpu)
>>           return -EINVAL;
>>       }
>>   +    /*
>> +     * We don't use mapped IRQs for Realms because the RMI doesn't allow
>> +     * us setting the LR.HW bit in the VGIC.
>> +     */
>> +    if (vcpu_is_rec(vcpu))
>> +        return 0;
>> +
>>       get_timer_map(vcpu, &map);
>>         ret = kvm_vgic_map_phys_irq(vcpu,
>> diff --git a/include/kvm/arm_arch_timer.h b/include/kvm/arm_arch_timer.h
>> index cd6d8f260eab..158280e15a33 100644
>> --- a/include/kvm/arm_arch_timer.h
>> +++ b/include/kvm/arm_arch_timer.h
>> @@ -76,6 +76,8 @@ int kvm_arm_timer_set_attr(struct kvm_vcpu *vcpu,
>> struct kvm_device_attr *attr);
>>   int kvm_arm_timer_get_attr(struct kvm_vcpu *vcpu, struct
>> kvm_device_attr *attr);
>>   int kvm_arm_timer_has_attr(struct kvm_vcpu *vcpu, struct
>> kvm_device_attr *attr);
>>   +void kvm_realm_timers_update(struct kvm_vcpu *vcpu);
>> +
>>   u64 kvm_phys_timer_read(void);
>>     void kvm_timer_vcpu_load(struct kvm_vcpu *vcpu);
> 
> Thanks,
> Ganapat