Re: [kvmtool PATCH v9 06/15] PCI: Only allocate IRQ routing entry when available

[Marc Zyngier]

On Wed, Mar 29 2017 at  9:44:47 pm BST, André Przywara  
wrote:
> Hi Marc,
>
> thanks for having a look!
>
> On 29/03/17 09:30, Marc Zyngier wrote:
>> On 02/02/17 16:32, Andre Przywara wrote:
>>> If we need to inject an MSI into the guest, we rely at the moment on a
>>> working GSI MSI routing functionality. However we can get away without
>>> IRQ routing, if the host supports MSI injection via the KVM_SIGNAL_MSI
>>> ioctl.
>>> So we try the GSI routing first, but if that fails due to a missing
>>> IRQ routing functionality, we fall back to KVM_SIGNAL_MSI (if that is
>>> supported).
>>>
>>> Signed-off-by: Andre Przywara 
>>> ---
>>>  virtio/pci.c | 16 ++--
>>>  1 file changed, 14 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/virtio/pci.c b/virtio/pci.c
>>> index 7cc0ba4..98bf6b7 100644
>>> --- a/virtio/pci.c
>>> +++ b/virtio/pci.c
>>> @@ -193,8 +193,14 @@ static bool virtio_pci__specific_io_out(struct kvm 
>>> *kvm, struct virtio_device *v
>>>  
>>> gsi = irq__add_msix_route(kvm,
>>>   >msix_table[vec].msg);
>>> -   if (gsi >= 0)
>>> +   if (gsi >= 0) {
>>> vpci->config_gsi = gsi;
>>> +   break;
>>> +   }
>>> +   if (gsi == -ENXIO &&
>>> +   vpci->features & VIRTIO_PCI_F_SIGNAL_MSI)
>>> +   break;
>>> +   die("failed to configure MSIs");
>>> break;
>>> case VIRTIO_MSI_QUEUE_VECTOR:
>>> vec = ioport__read16(data);
>>> @@ -205,8 +211,14 @@ static bool virtio_pci__specific_io_out(struct kvm 
>>> *kvm, struct virtio_device *v
>>>  
>>> gsi = irq__add_msix_route(kvm,
>>>   >msix_table[vec].msg);
>>> -   if (gsi < 0)
>>> +   if (gsi < 0) {
>>> +   if (gsi == -ENXIO &&
>>> +   vpci->features & VIRTIO_PCI_F_SIGNAL_MSI)
>>> +   break;
>>> +
>>> +   die("failed to configure MSIs");
>>> break;
>>> +   }
>>> vpci->gsis[vpci->queue_selector] = gsi;
>> 
>> Is it really expected to find -ENXIO in this array instead of a GSI?
>
> Not sure I get this "in this array" comment here. Any negative return
> value ends up in a break, without writing it anywhere.
> Later on we check for VIRTIO_PCI_F_SIGNAL_MSI first before referencing
> the array. This is admittedly a bit convoluted.
> So shall I add comments here? Or rewrite the if statement to make this
> more obvious?

Ah! Of course you're right, I completely misread the code. Maybe indeed
rewriting a bit to make it more obvious:

if (gsi == -ENXIO && vpci->features & VIRTIO_PCI_F_SIGNAL_MSI)
break;
if (gsi < 0) {
die("failed to configure MSIs");
break
}

which is closer to the first.

Thanks,

M.
-- 
Jazz is not dead, it just smell funny.
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Re: [kvmtool PATCH v9 06/15] PCI: Only allocate IRQ routing entry when available

[André Przywara]

Hi Marc,

thanks for having a look!

On 29/03/17 09:30, Marc Zyngier wrote:
> On 02/02/17 16:32, Andre Przywara wrote:
>> If we need to inject an MSI into the guest, we rely at the moment on a
>> working GSI MSI routing functionality. However we can get away without
>> IRQ routing, if the host supports MSI injection via the KVM_SIGNAL_MSI
>> ioctl.
>> So we try the GSI routing first, but if that fails due to a missing
>> IRQ routing functionality, we fall back to KVM_SIGNAL_MSI (if that is
>> supported).
>>
>> Signed-off-by: Andre Przywara 
>> ---
>>  virtio/pci.c | 16 ++--
>>  1 file changed, 14 insertions(+), 2 deletions(-)
>>
>> diff --git a/virtio/pci.c b/virtio/pci.c
>> index 7cc0ba4..98bf6b7 100644
>> --- a/virtio/pci.c
>> +++ b/virtio/pci.c
>> @@ -193,8 +193,14 @@ static bool virtio_pci__specific_io_out(struct kvm 
>> *kvm, struct virtio_device *v
>>  
>>  gsi = irq__add_msix_route(kvm,
>>>msix_table[vec].msg);
>> -if (gsi >= 0)
>> +if (gsi >= 0) {
>>  vpci->config_gsi = gsi;
>> +break;
>> +}
>> +if (gsi == -ENXIO &&
>> +vpci->features & VIRTIO_PCI_F_SIGNAL_MSI)
>> +break;
>> +die("failed to configure MSIs");
>>  break;
>>  case VIRTIO_MSI_QUEUE_VECTOR:
>>  vec = ioport__read16(data);
>> @@ -205,8 +211,14 @@ static bool virtio_pci__specific_io_out(struct kvm 
>> *kvm, struct virtio_device *v
>>  
>>  gsi = irq__add_msix_route(kvm,
>>>msix_table[vec].msg);
>> -if (gsi < 0)
>> +if (gsi < 0) {
>> +if (gsi == -ENXIO &&
>> +vpci->features & VIRTIO_PCI_F_SIGNAL_MSI)
>> +break;
>> +
>> +die("failed to configure MSIs");
>>  break;
>> +}
>>  vpci->gsis[vpci->queue_selector] = gsi;
> 
> Is it really expected to find -ENXIO in this array instead of a GSI?

Not sure I get this "in this array" comment here. Any negative return
value ends up in a break, without writing it anywhere.
Later on we check for VIRTIO_PCI_F_SIGNAL_MSI first before referencing
the array. This is admittedly a bit convoluted.
So shall I add comments here? Or rewrite the if statement to make this
more obvious?

Cheers,
Andre.

> 
>>  if (vdev->ops->notify_vq_gsi)
>>  vdev->ops->notify_vq_gsi(kvm, vpci->dev,
>>
> 
> Thanks,
> 
>   M.
> 

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Re: [kvmtool PATCH v9 06/15] PCI: Only allocate IRQ routing entry when available

[Marc Zyngier]

On 02/02/17 16:32, Andre Przywara wrote:
> If we need to inject an MSI into the guest, we rely at the moment on a
> working GSI MSI routing functionality. However we can get away without
> IRQ routing, if the host supports MSI injection via the KVM_SIGNAL_MSI
> ioctl.
> So we try the GSI routing first, but if that fails due to a missing
> IRQ routing functionality, we fall back to KVM_SIGNAL_MSI (if that is
> supported).
> 
> Signed-off-by: Andre Przywara 
> ---
>  virtio/pci.c | 16 ++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/virtio/pci.c b/virtio/pci.c
> index 7cc0ba4..98bf6b7 100644
> --- a/virtio/pci.c
> +++ b/virtio/pci.c
> @@ -193,8 +193,14 @@ static bool virtio_pci__specific_io_out(struct kvm *kvm, 
> struct virtio_device *v
>  
>   gsi = irq__add_msix_route(kvm,
> >msix_table[vec].msg);
> - if (gsi >= 0)
> + if (gsi >= 0) {
>   vpci->config_gsi = gsi;
> + break;
> + }
> + if (gsi == -ENXIO &&
> + vpci->features & VIRTIO_PCI_F_SIGNAL_MSI)
> + break;
> + die("failed to configure MSIs");
>   break;
>   case VIRTIO_MSI_QUEUE_VECTOR:
>   vec = ioport__read16(data);
> @@ -205,8 +211,14 @@ static bool virtio_pci__specific_io_out(struct kvm *kvm, 
> struct virtio_device *v
>  
>   gsi = irq__add_msix_route(kvm,
> >msix_table[vec].msg);
> - if (gsi < 0)
> + if (gsi < 0) {
> + if (gsi == -ENXIO &&
> + vpci->features & VIRTIO_PCI_F_SIGNAL_MSI)
> + break;
> +
> + die("failed to configure MSIs");
>   break;
> + }
>   vpci->gsis[vpci->queue_selector] = gsi;

Is it really expected to find -ENXIO in this array instead of a GSI?

>   if (vdev->ops->notify_vq_gsi)
>   vdev->ops->notify_vq_gsi(kvm, vpci->dev,
> 

Thanks,

M.
-- 
Jazz is not dead. It just smells funny...
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[kvmtool PATCH v9 06/15] PCI: Only allocate IRQ routing entry when available

[Andre Przywara]

If we need to inject an MSI into the guest, we rely at the moment on a
working GSI MSI routing functionality. However we can get away without
IRQ routing, if the host supports MSI injection via the KVM_SIGNAL_MSI
ioctl.
So we try the GSI routing first, but if that fails due to a missing
IRQ routing functionality, we fall back to KVM_SIGNAL_MSI (if that is
supported).

Signed-off-by: Andre Przywara 
---
 virtio/pci.c | 16 ++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/virtio/pci.c b/virtio/pci.c
index 7cc0ba4..98bf6b7 100644
--- a/virtio/pci.c
+++ b/virtio/pci.c
@@ -193,8 +193,14 @@ static bool virtio_pci__specific_io_out(struct kvm *kvm, 
struct virtio_device *v
 
gsi = irq__add_msix_route(kvm,
  >msix_table[vec].msg);
-   if (gsi >= 0)
+   if (gsi >= 0) {
vpci->config_gsi = gsi;
+   break;
+   }
+   if (gsi == -ENXIO &&
+   vpci->features & VIRTIO_PCI_F_SIGNAL_MSI)
+   break;
+   die("failed to configure MSIs");
break;
case VIRTIO_MSI_QUEUE_VECTOR:
vec = ioport__read16(data);
@@ -205,8 +211,14 @@ static bool virtio_pci__specific_io_out(struct kvm *kvm, 
struct virtio_device *v
 
gsi = irq__add_msix_route(kvm,
  >msix_table[vec].msg);
-   if (gsi < 0)
+   if (gsi < 0) {
+   if (gsi == -ENXIO &&
+   vpci->features & VIRTIO_PCI_F_SIGNAL_MSI)
+   break;
+
+   die("failed to configure MSIs");
break;
+   }
vpci->gsis[vpci->queue_selector] = gsi;
if (vdev->ops->notify_vq_gsi)
vdev->ops->notify_vq_gsi(kvm, vpci->dev,
-- 
2.9.0

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