[PATCH] KVM: arm/arm64 : add lpi info in vgic-debug
Marc Zyngier
marc.zyngier at arm.com
Fri Mar 23 07:45:32 PDT 2018
[fixing Christoffer's email address]
On 23/03/18 13:33, peng.hao2 at zte.com.cn wrote:
>> On 23/03/18 10:36, Peng Hao wrote:
>>> Add lpi debug info to vgic-stat.
>>> the printed info like this:
>>> SPI 287 0 000001 0 0 0 160 -1
>>> LPI 8192 2 000100 0 0 0 160 -1
>>>
>>> Signed-off-by: Peng Hao <peng.hao2 at zte.com.cn>
>>> ---
>>> virt/kvm/arm/vgic/vgic-debug.c | 61 ++++++++++++++++++++++++++++++++++++++----
>>> 1 file changed, 56 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/virt/kvm/arm/vgic/vgic-debug.c b/virt/kvm/arm/vgic/vgic-debug.c
>>> index 10b3817..444115e 100644
>>> --- a/virt/kvm/arm/vgic/vgic-debug.c
>>> +++ b/virt/kvm/arm/vgic/vgic-debug.c
>>> @@ -36,9 +36,12 @@
>>> struct vgic_state_iter {
>>> int nr_cpus;
>>> int nr_spis;
>>> + int nr_lpis;
>>> int dist_id;
>>> int vcpu_id;
>>> int intid;
>>> + int lpi_print_count;
>>> + struct vgic_irq **lpi_irqs;
>>> };
>>>
>>> static void iter_next(struct vgic_state_iter *iter)
>>> @@ -52,6 +55,40 @@ static void iter_next(struct vgic_state_iter *iter)
>>> if (iter->intid == VGIC_NR_PRIVATE_IRQS &&
>>> ++iter->vcpu_id < iter->nr_cpus)
>>> iter->intid = 0;
>>> +
>>> + if (iter->intid >= VGIC_NR_PRIVATE_IRQS + iter->nr_spis) {
>>> + if (iter->lpi_print_count < iter->nr_lpis)
>>> + iter->intid = iter->lpi_irqs[iter->lpi_print_count]->intid;
>>> + iter->lpi_print_count++;
>>> + }
>>> +}
>>> +
>>> +static void vgic_debug_get_lpis(struct kvm *kvm, struct vgic_state_iter *iter)
>>> +{
>>> + struct vgic_dist *dist = &kvm->arch.vgic;
>>> + int i = 0;
>>> + struct vgic_irq *irq = NULL, **lpi_irqs;
>>> +
>>> +again:
>>> + iter->nr_lpis = dist->lpi_list_count;
>>> + lpi_irqs = kmalloc_array(iter->nr_lpis, sizeof(irq), GFP_KERNEL);
>>> + if (!lpi_irqs) {
>>> + iter->nr_lpis = 0;
>>> + return;
>>> + }
>>> + spin_lock(&dist->lpi_list_lock);
>>> + if (iter->nr_lpis != dist->lpi_list_count) {
>>> + kfree(lpi_irqs);
>>> + spin_unlock(&dist->lpi_list_lock);
>>> + goto again;
>>> + }
>
>> Why do we need an exact count? It is fine to have a transient count, and
>> the debug code should be able to come with that without performing this
>> terrible loop.
> yeah, it is enough to have a rough count for debug code .
>> We also already have some code that snapshot the the LPIs (see
>> vgic_copy_lpi_list), so please consider reusing that instead.
> I can't reuse vgic_copy_lpi_list. It snapshots based on LPI's target vcpu.
Guess what? You can also change it!
>>> +
>>> + list_for_each_entry(irq, &dist->lpi_list_head, lpi_list) {
>>> + vgic_get_irq_kref(irq);
>>> + lpi_irqs[i++] = irq;
>>> + }
>>> + spin_unlock(&dist->lpi_list_lock);
>>> + iter->lpi_irqs = lpi_irqs;
>
>> Messing with the internals of the refcounts is really a bad idea. Please
>> use vgic_get_irq() in conjunction with the above, and allow it to fail
>> gracefully.
> vgic_get_irq require intid as input and vgic_get_lpi that vgic_get_irq calling will traverse the lpi_list with holding lpi_list_lock again,
> but here I has held lpi_list_lock. So I think calling vgic_get_irq_kref is safe with holding the
> lpi_list_lock.
It is safe but terribly ugly. Traversing the LPI list is completely
fine, and we have this API for a reason (not reinventing the wheel). I
don't think the debug code should sidestep it. If the list proves to be
too slow to traverse, then we should adopt a better data structure.
>>> }
>>>
>>> static void iter_init(struct kvm *kvm, struct vgic_state_iter *iter,
>>> @@ -64,6 +101,8 @@ static void iter_init(struct kvm *kvm, struct vgic_state_iter *iter,
>>> iter->nr_cpus = nr_cpus;
>>> iter->nr_spis = kvm->arch.vgic.nr_spis;
>>>
>>> + if (vgic_supports_direct_msis(kvm) && !pos)
>>> + vgic_debug_get_lpis(kvm, iter);
BTW, what's the point of this?
>>> /* Fast forward to the right position if needed */
>>> while (pos--)
>>> iter_next(iter);
>>> @@ -73,7 +112,9 @@ static bool end_of_vgic(struct vgic_state_iter *iter)
>>> {
>>> return iter->dist_id > 0 &&
>>> iter->vcpu_id == iter->nr_cpus &&
>>> - (iter->intid - VGIC_NR_PRIVATE_IRQS) == iter->nr_spis;
>>> + (iter->intid - VGIC_NR_PRIVATE_IRQS) >= iter->nr_spis &&
>>> + ((iter->nr_lpis == 0) ||
>>> + (iter->lpi_print_count == iter->nr_lpis + 1));
>>> }
>>>
>>> static void *vgic_debug_start(struct seq_file *s, loff_t *pos)
>>> @@ -130,6 +171,7 @@ static void vgic_debug_stop(struct seq_file *s, void *v)
>>>
>>> mutex_lock(&kvm->lock);
>>> iter = kvm->arch.vgic.iter;
>>> + kfree(iter->lpi_irqs);
>>> kfree(iter);
>>> kvm->arch.vgic.iter = NULL;
>>> mutex_unlock(&kvm->lock);
>>> @@ -154,7 +196,7 @@ static void print_header(struct seq_file *s, struct vgic_irq *irq,
>>> struct kvm_vcpu *vcpu)
>>> {
>>> int id = 0;
>>> - char *hdr = "SPI ";
>>> + char *hdr = "S/LPI ";
>>>
>>> if (vcpu) {
>>> hdr = "VCPU";
>>> @@ -162,7 +204,10 @@ static void print_header(struct seq_file *s, struct vgic_irq *irq,
>>> }
>>>
>>> seq_printf(s, "\n");
>>> - seq_printf(s, "%s%2d TYP ID TGT_ID PLAEHC HWID TARGET SRC PRI VCPU_ID\n", hdr, id);
>>> + if (vcpu)
>>> + seq_printf(s, "%s%2d TYP ID TGT_ID PLAEHC HWID TARGET SRC PRI VCPU_ID\n", hdr, id);
>>> + else
>>> + seq_printf(s, "%s TYP ID TGT_ID PLAEHC HWID TARGET SRC PRI VCPU_ID\n", hdr);
>
>> This feels like an unnecessary change. But if you really want that kind
>> of detail, change your "S/LPI" to say something more generic, such as
>> "Global".
> I modify this just for aligned print output. "Global" is great.
>>> seq_printf(s, "---------------------------------------------------------------\n");> }
>>>
>>> @@ -174,8 +219,10 @@ static void print_irq_state(struct seq_file *s, struct vgic_irq *irq,
>>> type = "SGI";
>>> else if (irq->intid < VGIC_NR_PRIVATE_IRQS)
>>> type = "PPI";
>>> - else
>>> + else if (irq->intid < VGIC_MAX_SPI)
>>> type = "SPI";
>>> + else if (irq->intid >= VGIC_MIN_LPI)
>>> + type = "LPI";
>>>
>>> if (irq->intid ==0 || irq->intid == VGIC_NR_PRIVATE_IRQS)
>>> print_header(s, irq, vcpu);
>>> @@ -220,7 +267,9 @@ static int vgic_debug_show(struct seq_file *s, void *v)
>>> if (!kvm->arch.vgic.initialized)
>>> return 0;
>>>
>>> - if (iter->vcpu_id < iter->nr_cpus) {
>>> + if (iter->intid >= VGIC_MIN_LPI)
>>> + irq = iter->lpi_irqs[iter->lpi_print_count - 1];
>>> + else if (iter->vcpu_id < iter->nr_cpus) {
>>> vcpu = kvm_get_vcpu(kvm, iter->vcpu_id);
>>> irq = &vcpu->arch.vgic_cpu.private_irqs[iter->intid];
>>> } else {
>>> @@ -230,6 +279,8 @@ static int vgic_debug_show(struct seq_file *s, void *v)
>>> spin_lock(&irq->irq_lock);
>>> print_irq_state(s, irq, vcpu);
>>> spin_unlock(&irq->irq_lock);
>>> + if (iter->intid >= VGIC_MIN_LPI)
>>> + vgic_put_irq(kvm, irq);
>
>> If you adopt the scheme I outlined above, you can have a balanced
>> get/put behaviour, irrespective of the interrupt type, and a much nicer
>> result.
> yeah, "if (iter->intid >= VGIC_MIN_LPI)" is unnecessary.
I'm still adamant that you should have get/put for every interrupt. It
won't cost anything, and the code will look better.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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