Subject: [PATCH v3 06/19] KVM: ARM: vgic: introduce vgic_ops and LR manipulation primitives

From: [email-masked] (Marc Zyngier)
Date: Mon, 12 May 2014 18:28:19 +0100

On Fri, May 09 2014 at  3:05:54 pm BST, Christoffer Dall <[email-masked]> wrote:
> On Wed, Apr 16, 2014 at 02:39:38PM +0100, Marc Zyngier wrote:
>> In order to split the various register manipulation from the main vgic
>> code, introduce a vgic_ops structure, and start by abstracting the
>> LR manipulation code with a couple of accessors.
>>
>> Signed-off-by: Marc Zyngier <[email-masked]>
>> ---
>>  include/kvm/arm_vgic.h |  18 ++++++
>>  virt/kvm/arm/vgic.c    | 170 +++++++++++++++++++++++++++++++++----------------
>>  2 files changed, 132 insertions(+), 56 deletions(-)
>>
>> diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
>> index f738e5a..17bbe51 100644
>> --- a/include/kvm/arm_vgic.h
>> +++ b/include/kvm/arm_vgic.h
>> @@ -68,6 +68,24 @@ struct vgic_bytemap {
>>       u32 shared[VGIC_NR_SHARED_IRQS  / 4];
>>  };
>>
>> +struct kvm_vcpu;
>> +
>> +#define LR_STATE_PENDING     (1 << 0)
>> +#define LR_STATE_ACTIVE              (1 << 1)
>> +#define LR_STATE_MASK                (3 << 0)
>> +#define LR_EOI_INT           (1 << 2)
>> +
>> +struct vgic_lr {
>> +     u16     irq;
>> +     u8      source;
>> +     u8      state;
>> +};
>> +
>> +struct vgic_ops {
>> +     struct vgic_lr  (*get_lr)(const struct kvm_vcpu *, int);
>> +     void    (*set_lr)(struct kvm_vcpu *, int, struct vgic_lr);
>> +};
>> +
>>  struct vgic_dist {
>>  #ifdef CONFIG_KVM_ARM_VGIC
>>       spinlock_t              lock;
>> diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
>> index 6bc6c7a..bac37b8 100644
>> --- a/virt/kvm/arm/vgic.c
>> +++ b/virt/kvm/arm/vgic.c
>> @@ -94,9 +94,12 @@ static struct device_node *vgic_node;
>>  #define ACCESS_WRITE_MASK(x) ((x) & (3 << 1))
>>
>>  static void vgic_retire_disabled_irqs(struct kvm_vcpu *vcpu);
>> +static void vgic_retire_lr(int lr_nr, int irq, struct kvm_vcpu *vcpu);
>>  static void vgic_update_state(struct kvm *kvm);
>>  static void vgic_kick_vcpus(struct kvm *kvm);
>>  static void vgic_dispatch_sgi(struct kvm_vcpu *vcpu, u32 reg);
>> +static struct vgic_lr vgic_get_lr(const struct kvm_vcpu *vcpu, int lr);
>> +static void vgic_set_lr(struct kvm_vcpu *vcpu, int lr, struct vgic_lr lr_desc);
>>  static u32 vgic_nr_lr;
>>
>>  static unsigned int vgic_maint_irq;
>> @@ -594,18 +597,6 @@ static bool handle_mmio_sgi_reg(struct kvm_vcpu *vcpu,
>>       return false;
>>  }
>>
>> -#define LR_CPUID(lr) \
>> -     (((lr) & GICH_LR_PHYSID_CPUID) >> GICH_LR_PHYSID_CPUID_SHIFT)
>> -#define LR_IRQID(lr) \
>> -     ((lr) & GICH_LR_VIRTUALID)
>> -
>> -static void vgic_retire_lr(int lr_nr, int irq, struct vgic_cpu *vgic_cpu)
>> -{
>> -     clear_bit(lr_nr, vgic_cpu->lr_used);
>> -     vgic_cpu->vgic_v2.vgic_lr[lr_nr] &= ~GICH_LR_STATE;
>> -     vgic_cpu->vgic_irq_lr_map[irq] = LR_EMPTY;
>> -}
>> -
>>  /**
>>   * vgic_unqueue_irqs - move pending IRQs from LRs to the distributor
>>   * @vgic_cpu: Pointer to the vgic_cpu struct holding the LRs
>> @@ -623,13 +614,10 @@ static void vgic_unqueue_irqs(struct kvm_vcpu *vcpu)
>>       struct vgic_dist *dist = &vcpu->kvm->arch.vgic;
>>       struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
>>       int vcpu_id = vcpu->vcpu_id;
>> -     int i, irq, source_cpu;
>> -     u32 *lr;
>> +     int i;
>>
>>       for_each_set_bit(i, vgic_cpu->lr_used, vgic_cpu->nr_lr) {
>> -             lr = &vgic_cpu->vgic_v2.vgic_lr[i];
>> -             irq = LR_IRQID(*lr);
>> -             source_cpu = LR_CPUID(*lr);
>> +             struct vgic_lr lr = vgic_get_lr(vcpu, i);
>>
>>               /*
>>                * There are three options for the state bits:
>> @@ -641,7 +629,7 @@ static void vgic_unqueue_irqs(struct kvm_vcpu *vcpu)
>>                * If the LR holds only an active interrupt (not pending) then
>>                * just leave it alone.
>>                */
>> -             if ((*lr & GICH_LR_STATE) == GICH_LR_ACTIVE_BIT)
>> +             if ((lr.state & LR_STATE_MASK) == LR_STATE_ACTIVE)
>>                       continue;
>>
>>               /*
>> @@ -650,18 +638,19 @@ static void vgic_unqueue_irqs(struct kvm_vcpu *vcpu)
>>                * is fine, then we are only setting a few bits that were
>>                * already set.
>>                */
>> -             vgic_dist_irq_set(vcpu, irq);
>> -             if (irq < VGIC_NR_SGIS)
>> -                     dist->irq_sgi_sources[vcpu_id][irq] |= 1 << source_cpu;
>> -             *lr &= ~GICH_LR_PENDING_BIT;
>> +             vgic_dist_irq_set(vcpu, lr.irq);
>> +             if (lr.irq < VGIC_NR_SGIS)
>> +                     dist->irq_sgi_sources[vcpu_id][lr.irq] |= 1 << lr.source;
>> +             lr.state &= ~LR_STATE_PENDING;
>> +             vgic_set_lr(vcpu, i, lr);
>>
>>               /*
>>                * If there's no state left on the LR (it could still be
>>                * active), then the LR does not hold any useful info and can
>>                * be marked as free for other use.
>>                */
>> -             if (!(*lr & GICH_LR_STATE))
>> -                     vgic_retire_lr(i, irq, vgic_cpu);
>> +             if (!(lr.state & LR_STATE_MASK))
>> +                     vgic_retire_lr(i, lr.irq, vcpu);
>>
>>               /* Finally update the VGIC state. */
>>               vgic_update_state(vcpu->kvm);
>> @@ -989,9 +978,77 @@ static void vgic_update_state(struct kvm *kvm)
>>       }
>>  }
>>
>> +static struct vgic_lr vgic_v2_get_lr(const struct kvm_vcpu *vcpu, int lr)
>> +{
>> +     struct vgic_lr lr_desc;
>> +     u32 val = vcpu->arch.vgic_cpu.vgic_v2.vgic_lr[lr];
>> +
>> +     lr_desc.irq     = val & GICH_LR_VIRTUALID;
>> +     lr_desc.source  = (val >> GICH_LR_PHYSID_CPUID_SHIFT) & 0xff;
>
> shouldn't the mask here be 0xf according to the GICv2 spec?

Actually, looks like it should be 7 instead (bits [12:10], and only when
lr_desc.irq is within 0..15). Well spotted anyway.

>
>> +     lr_desc.state   = 0;
>> +
>> +     if (val & GICH_LR_PENDING_BIT)
>> +             lr_desc.state |= LR_STATE_PENDING;
>> +     if (val & GICH_LR_ACTIVE_BIT)
>> +             lr_desc.state |= LR_STATE_ACTIVE;
>> +     if (val & GICH_LR_EOI)
>> +             lr_desc.state |= LR_EOI_INT;
>> +
>> +     return lr_desc;
>> +}
>> +
>>  #define MK_LR_PEND(src, irq) \
>>       (GICH_LR_PENDING_BIT | ((src) << GICH_LR_PHYSID_CPUID_SHIFT) | (irq))
>>
>> +static void vgic_v2_set_lr(struct kvm_vcpu *vcpu, int lr,
>> +                        struct vgic_lr lr_desc)
>> +{
>> +     u32 lr_val = MK_LR_PEND(lr_desc.source, lr_desc.irq);
>
> this looks a bit weird, the check just below suggests that you can
> convert a struct vgic_lr into an lr register for, for example, an lr
> which is just active and not pending.

Ah, this is probably a leftover from some previous implementation. I'll
get rid of MR_LR_PEND altogether, and rely solely on lr_desc.state.

>> +
>> +     if (lr_desc.state & LR_STATE_PENDING)
>> +             lr_val |= GICH_LR_PENDING_BIT;
>> +     if (lr_desc.state & LR_STATE_ACTIVE)
>> +             lr_val |= GICH_LR_ACTIVE_BIT;
>> +     if (lr_desc.state & LR_EOI_INT)
>> +             lr_val |= GICH_LR_EOI;
>> +
>> +     vcpu->arch.vgic_cpu.vgic_v2.vgic_lr[lr] = lr_val;
>> +
>> +     /*
>> +      * Despite being EOIed, the LR may not have been marked as
>> +      * empty.
>> +      */
>> +     if (!(lr_val & GICH_LR_STATE))
>> +             set_bit(lr, (unsigned long *)vcpu->arch.vgic_cpu.vgic_v2.vgic_elrsr);
>
> This feels weird in vgic_v2_set_lr, the name/style suggests that these
> get/set functions are just converters from a struct vgic_lr (that
> presumably common code can deal with) and architecture-specific LR
> register formats.
>
> If these functions have richer semantics than that (like maintaining the
> elrsr register), please comment that on the function.

Yeah, this is one of the corners I really dislike, but making this a
separate vector makes things even more ugly than they already are.

I'll add some comments, but feel free to suggest an alternative approach.

>> +}
>> +
>> +static const struct vgic_ops vgic_ops = {
>> +     .get_lr                 = vgic_v2_get_lr,
>> +     .set_lr                 = vgic_v2_set_lr,
>> +};
>> +
>> +static inline struct vgic_lr vgic_get_lr(const struct kvm_vcpu *vcpu, int lr)
>> +{
>> +     return vgic_ops.get_lr(vcpu, lr);
>> +}
>> +
>> +static inline void vgic_set_lr(struct kvm_vcpu *vcpu, int lr,
>> +                            struct vgic_lr vlr)
>> +{
>> +     vgic_ops.set_lr(vcpu, lr, vlr);
>> +}
>
> inline statics in a C file?  Surely the compiler is smart enough to
> inline this without any hints.

Yup, brain fart here.

>> +
>> +static void vgic_retire_lr(int lr_nr, int irq, struct kvm_vcpu *vcpu)
>> +{
>> +     struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
>> +     struct vgic_lr vlr = vgic_get_lr(vcpu, lr_nr);
>
> seems like we're doing a lot of copying back and forward between the
> struct vgic_lr and the LRs on the vgic_cpu struct, I wonder if it makes
> more sense to only deal with it during the sync/flush functions, or
> maybe we end up messing with more state than necessary then?

We're doing a lot of them, but we actually don't have much copying. The
structure is small enough to fit in a single register (even on AArch32),
and we're passing it by value. So the whole state computation actually
occurs in registers.

But overall yes, I agree that we should probably try to do things in a
more staged way. I'll have a look.

>> +
>> +     vlr.state = 0;
>> +     vgic_set_lr(vcpu, lr_nr, vlr);
>> +     clear_bit(lr_nr, vgic_cpu->lr_used);
>> +     vgic_cpu->vgic_irq_lr_map[irq] = LR_EMPTY;
>> +}
>> +
>>  /*
>>   * An interrupt may have been disabled after being made pending on the
>>   * CPU interface (the classic case is a timer running while we're
>> @@ -1007,12 +1064,12 @@ static void vgic_retire_disabled_irqs(struct kvm_vcpu *vcpu)
>>       int lr;
>>
>>       for_each_set_bit(lr, vgic_cpu->lr_used, vgic_cpu->nr_lr) {
>> -             int irq = vgic_cpu->vgic_v2.vgic_lr[lr] & GICH_LR_VIRTUALID;
>> +             struct vgic_lr vlr = vgic_get_lr(vcpu, lr);
>>
>> -             if (!vgic_irq_is_enabled(vcpu, irq)) {
>> -                     vgic_retire_lr(lr, irq, vgic_cpu);
>> -                     if (vgic_irq_is_active(vcpu, irq))
>> -                             vgic_irq_clear_active(vcpu, irq);
>> +             if (!vgic_irq_is_enabled(vcpu, vlr.irq)) {
>> +                     vgic_retire_lr(lr, vlr.irq, vcpu);
>> +                     if (vgic_irq_is_active(vcpu, vlr.irq))
>> +                             vgic_irq_clear_active(vcpu, vlr.irq);
>>               }
>>       }
>>  }
>> @@ -1024,6 +1081,7 @@ static void vgic_retire_disabled_irqs(struct kvm_vcpu *vcpu)
>>  static bool vgic_queue_irq(struct kvm_vcpu *vcpu, u8 sgi_source_id, int irq)
>>  {
>>       struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
>> +     struct vgic_lr vlr;
>>       int lr;
>>
>>       /* Sanitize the input... */
>> @@ -1036,13 +1094,15 @@ static bool vgic_queue_irq(struct kvm_vcpu *vcpu, u8 sgi_source_id, int irq)
>>       lr = vgic_cpu->vgic_irq_lr_map[irq];
>>
>>       /* Do we have an active interrupt for the same CPUID? */
>> -     if (lr != LR_EMPTY &&
>> -         (LR_CPUID(vgic_cpu->vgic_v2.vgic_lr[lr]) == sgi_source_id)) {
>> -             kvm_debug("LR%d piggyback for IRQ%d %x\n",
>> -                       lr, irq, vgic_cpu->vgic_v2.vgic_lr[lr]);
>> -             BUG_ON(!test_bit(lr, vgic_cpu->lr_used));
>> -             vgic_cpu->vgic_v2.vgic_lr[lr] |= GICH_LR_PENDING_BIT;
>> -             return true;
>> +     if (lr != LR_EMPTY) {
>> +             vlr = vgic_get_lr(vcpu, lr);
>> +             if (vlr.source == sgi_source_id) {
>> +                     kvm_debug("LR%d piggyback for IRQ%d\n", lr, vlr.irq);
>> +                     BUG_ON(!test_bit(lr, vgic_cpu->lr_used));
>> +                     vlr.state |= LR_STATE_PENDING;
>> +                     vgic_set_lr(vcpu, lr, vlr);
>> +                     return true;
>> +             }
>>       }
>>
>>       /* Try to use another LR for this interrupt */
>> @@ -1052,12 +1112,16 @@ static bool vgic_queue_irq(struct kvm_vcpu *vcpu, u8 sgi_source_id, int irq)
>>               return false;
>>
>>       kvm_debug("LR%d allocated for IRQ%d %x\n", lr, irq, sgi_source_id);
>> -     vgic_cpu->vgic_v2.vgic_lr[lr] = MK_LR_PEND(sgi_source_id, irq);
>>       vgic_cpu->vgic_irq_lr_map[irq] = lr;
>>       set_bit(lr, vgic_cpu->lr_used);
>>
>> +     vlr.irq = irq;
>> +     vlr.source = sgi_source_id;
>> +     vlr.state = LR_STATE_PENDING;
>>       if (!vgic_irq_is_edge(vcpu, irq))
>> -             vgic_cpu->vgic_v2.vgic_lr[lr] |= GICH_LR_EOI;
>> +             vlr.state |= LR_EOI_INT;
>> +
>> +     vgic_set_lr(vcpu, lr, vlr);
>>
>>       return true;
>>  }
>> @@ -1180,29 +1244,23 @@ static bool vgic_process_maintenance(struct kvm_vcpu *vcpu)
>>                * Some level interrupts have been EOIed. Clear their
>>                * active bit.
>>                */
>> -             int lr, irq;
>> +             int lr;
>>
>>               for_each_set_bit(lr, (unsigned long *)vgic_cpu->vgic_v2.vgic_eisr,
>>                                vgic_cpu->nr_lr) {
>> -                     irq = vgic_cpu->vgic_v2.vgic_lr[lr] & GICH_LR_VIRTUALID;
>> +                     struct vgic_lr vlr = vgic_get_lr(vcpu, lr);
>>
>> -                     vgic_irq_clear_active(vcpu, irq);
>> -                     vgic_cpu->vgic_v2.vgic_lr[lr] &= ~GICH_LR_EOI;
>> +                     vgic_irq_clear_active(vcpu, vlr.irq);
>> +                     vlr.state = 0;
>
> slight change of semantics here.  It is still correct, but only because
> we never set the pending bit on an already active level interrupt, but I
> guess this could technically be closer to real hardware by allowing
> world-switching VMs that are processing active interrupts to pick up an
> additional pending state, in which case just setting state = 0 would be
> incorrect here, and you should instead lower the EOI mask like you did
> before.
>
> That being said, it is a pseudo-theoretical point, and you can make me
> more happy by adding:
>
> BUG_ON(vlr.state & LR_STATE_MASK);
>
> before clearing the state completely.

Putting a BUG_ON() seems a bit harsh. WARN_ON()?

>> +                     vgic_set_lr(vcpu, lr, vlr);
>>
>>                       /* Any additional pending interrupt? */
>> -                     if (vgic_dist_irq_is_pending(vcpu, irq)) {
>> -                             vgic_cpu_irq_set(vcpu, irq);
>> +                     if (vgic_dist_irq_is_pending(vcpu, vlr.irq)) {
>> +                             vgic_cpu_irq_set(vcpu, vlr.irq);
>>                               level_pending = true;
>>                       } else {
>> -                             vgic_cpu_irq_clear(vcpu, irq);
>> +                             vgic_cpu_irq_clear(vcpu, vlr.irq);
>>                       }
>> -
>> -                     /*
>> -                      * Despite being EOIed, the LR may not have
>> -                      * been marked as empty.
>> -                      */
>> -                     set_bit(lr, (unsigned long *)vgic_cpu->vgic_v2.vgic_elrsr);
>> -                     vgic_cpu->vgic_v2.vgic_lr[lr] &= ~GICH_LR_ACTIVE_BIT;
>>               }
>>       }
>>
>> @@ -1228,15 +1286,15 @@ static void __kvm_vgic_sync_hwstate(struct kvm_vcpu *vcpu)
>>       /* Clear mappings for empty LRs */
>>       for_each_set_bit(lr, (unsigned long *)vgic_cpu->vgic_v2.vgic_elrsr,
>>                        vgic_cpu->nr_lr) {
>> -             int irq;
>> +             struct vgic_lr vlr;
>>
>>               if (!test_and_clear_bit(lr, vgic_cpu->lr_used))
>>                       continue;
>>
>> -             irq = vgic_cpu->vgic_v2.vgic_lr[lr] & GICH_LR_VIRTUALID;
>> +             vlr = vgic_get_lr(vcpu, lr);
>>
>> -             BUG_ON(irq >= VGIC_NR_IRQS);
>> -             vgic_cpu->vgic_irq_lr_map[irq] = LR_EMPTY;
>> +             BUG_ON(vlr.irq >= VGIC_NR_IRQS);
>> +             vgic_cpu->vgic_irq_lr_map[vlr.irq] = LR_EMPTY;
>>       }
>>
>>       /* Check if we still have something up our sleeve... */
>> --
>> 1.8.3.4
>>
> -Christoffer
>

-- 
Jazz is not dead. It just smells funny.