Re: [Qemu-devel] [PATCH 2/3] virtio-pci: add an option to bypass guest_notifier_mask

[Didier Pallard <didier.pallard@6wind.com>]

On 02/04/2016 02:08 PM, Michael S. Tsirkin wrote:
> On Thu, Dec 03, 2015 at 10:53:18AM +0100, Didier Pallard wrote:
>> Using guest_notifier_mask function in vhost-user case may
>> break interrupt mask paradigm, because mask/unmask is not
>> really done when returning from guest_notifier_mask call, instead
>> message is posted in a unix socket, and processed later.
>>
>> Add an option bit to disable the use of guest_notifier_mask
>> in virtio pci.
>>
>> Signed-off-by: Didier Pallard <didier.pallard@6wind.com>
>> Reviewed-by: Thibaut Collet <thibaut.collet@6wind.com>
>> ---
>>   hw/virtio/virtio-pci.c | 29 +++++++++++++++++++++++------
>>   hw/virtio/virtio-pci.h |  6 ++++++
>>   2 files changed, 29 insertions(+), 6 deletions(-)
>>
>> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
>> index dd48562..26bb617 100644
>> --- a/hw/virtio/virtio-pci.c
>> +++ b/hw/virtio/virtio-pci.c
>> @@ -806,7 +806,8 @@ static int kvm_virtio_pci_vector_use(VirtIOPCIProxy *proxy, int nvqs)
>>           /* If guest supports masking, set up irqfd now.
>>            * Otherwise, delay until unmasked in the frontend.
>>            */
>> -        if (k->guest_notifier_mask) {
>> +        if ((proxy->flags & VIRTIO_PCI_FLAG_USE_NOTIFIERMASK) &&
>> +            k->guest_notifier_mask) {
>>               ret = kvm_virtio_pci_irqfd_use(proxy, queue_no, vector);
>>               if (ret < 0) {
>>                   kvm_virtio_pci_vq_vector_release(proxy, vector);
>> @@ -822,7 +823,8 @@ undo:
>>           if (vector >= msix_nr_vectors_allocated(dev)) {
>>               continue;
>>           }
>> -        if (k->guest_notifier_mask) {
>> +        if ((proxy->flags & VIRTIO_PCI_FLAG_USE_NOTIFIERMASK) &&
>> +            k->guest_notifier_mask) {
>>               kvm_virtio_pci_irqfd_release(proxy, queue_no, vector);
>>           }
>>           kvm_virtio_pci_vq_vector_release(proxy, vector);
>> @@ -849,7 +851,8 @@ static void kvm_virtio_pci_vector_release(VirtIOPCIProxy *proxy, int nvqs)
>>           /* If guest supports masking, clean up irqfd now.
>>            * Otherwise, it was cleaned when masked in the frontend.
>>            */
>> -        if (k->guest_notifier_mask) {
>> +        if ((proxy->flags & VIRTIO_PCI_FLAG_USE_NOTIFIERMASK) &&
>> +            k->guest_notifier_mask) {
>>               kvm_virtio_pci_irqfd_release(proxy, queue_no, vector);
>>           }
>>           kvm_virtio_pci_vq_vector_release(proxy, vector);
>> @@ -882,7 +885,8 @@ static int virtio_pci_vq_vector_unmask(VirtIOPCIProxy *proxy,
>>       /* If guest supports masking, irqfd is already setup, unmask it.
>>        * Otherwise, set it up now.
>>        */
>> -    if (k->guest_notifier_mask) {
>> +    if ((proxy->flags & VIRTIO_PCI_FLAG_USE_NOTIFIERMASK) &&
>> +        k->guest_notifier_mask) {
>>           k->guest_notifier_mask(vdev, queue_no, false);
>>           /* Test after unmasking to avoid losing events. */
>>           if (k->guest_notifier_pending &&
>> @@ -905,7 +909,8 @@ static void virtio_pci_vq_vector_mask(VirtIOPCIProxy *proxy,
>>       /* If guest supports masking, keep irqfd but mask it.
>>        * Otherwise, clean it up now.
>>        */
>> -    if (k->guest_notifier_mask) {
>> +    if ((proxy->flags & VIRTIO_PCI_FLAG_USE_NOTIFIERMASK) &&
>> +        k->guest_notifier_mask) {
>>           k->guest_notifier_mask(vdev, queue_no, true);
>>       } else {
>>           kvm_virtio_pci_irqfd_release(proxy, queue_no, vector);
>> @@ -1022,7 +1027,9 @@ static int virtio_pci_set_guest_notifier(DeviceState *d, int n, bool assign,
>>           event_notifier_cleanup(notifier);
>>       }
>>   
>> -    if (!msix_enabled(&proxy->pci_dev) && vdc->guest_notifier_mask) {
>> +    if (!msix_enabled(&proxy->pci_dev) &&
>> +        (proxy->flags & VIRTIO_PCI_FLAG_USE_NOTIFIERMASK) &&
>> +        vdc->guest_notifier_mask) {
>>           vdc->guest_notifier_mask(vdev, n, !assign);
>>       }
>>   
>> @@ -1164,6 +1171,8 @@ static void virtio_9p_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
>>   static Property virtio_9p_pci_properties[] = {
>>       DEFINE_PROP_BIT("ioeventfd", VirtIOPCIProxy, flags,
>>                       VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT, true),
>> +    DEFINE_PROP_BIT("usenotifiermask", VirtIOPCIProxy, flags,
>> +                    VIRTIO_PCI_FLAG_USE_NOTIFIERMASK_BIT, true),
>>       DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors, 2),
>>       DEFINE_PROP_END_OF_LIST(),
>>   };
>> @@ -1908,6 +1917,8 @@ static Property virtio_blk_pci_properties[] = {
>>       DEFINE_PROP_UINT32("class", VirtIOPCIProxy, class_code, 0),
>>       DEFINE_PROP_BIT("ioeventfd", VirtIOPCIProxy, flags,
>>                       VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT, true),
>> +    DEFINE_PROP_BIT("usenotifiermask", VirtIOPCIProxy, flags,
>> +                    VIRTIO_PCI_FLAG_USE_NOTIFIERMASK_BIT, true),
>>       DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors, 2),
>>       DEFINE_PROP_END_OF_LIST(),
>>   };
>> @@ -1961,6 +1972,8 @@ static const TypeInfo virtio_blk_pci_info = {
>>   static Property virtio_scsi_pci_properties[] = {
>>       DEFINE_PROP_BIT("ioeventfd", VirtIOPCIProxy, flags,
>>                       VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT, true),
>> +    DEFINE_PROP_BIT("usenotifiermask", VirtIOPCIProxy, flags,
>> +                    VIRTIO_PCI_FLAG_USE_NOTIFIERMASK_BIT, true),
>>       DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors,
>>                          DEV_NVECTORS_UNSPECIFIED),
>>       DEFINE_PROP_END_OF_LIST(),
>> @@ -2175,6 +2188,8 @@ static void virtio_serial_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
>>   static Property virtio_serial_pci_properties[] = {
>>       DEFINE_PROP_BIT("ioeventfd", VirtIOPCIProxy, flags,
>>                       VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT, true),
>> +    DEFINE_PROP_BIT("usenotifiermask", VirtIOPCIProxy, flags,
>> +                    VIRTIO_PCI_FLAG_USE_NOTIFIERMASK_BIT, true),
>>       DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors, 2),
>>       DEFINE_PROP_UINT32("class", VirtIOPCIProxy, class_code, 0),
>>       DEFINE_PROP_END_OF_LIST(),
>> @@ -2215,6 +2230,8 @@ static const TypeInfo virtio_serial_pci_info = {
>>   static Property virtio_net_properties[] = {
>>       DEFINE_PROP_BIT("ioeventfd", VirtIOPCIProxy, flags,
>>                       VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT, false),
>> +    DEFINE_PROP_BIT("usenotifiermask", VirtIOPCIProxy, flags,
>> +                    VIRTIO_PCI_FLAG_USE_NOTIFIERMASK_BIT, true),
>>       DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors, 3),
>>       DEFINE_PROP_END_OF_LIST(),
>>   };
> I think we should rename this x-use-notifier mask.
> And I'd rather drop it from all devices where it's not relevant.
I will rename the option x-use-notifier-mask.
Currently, only vhost-net has a vhost-user implementation, isn't it?
so it is the only place were i need to set the option, that's it?

>
>> diff --git a/hw/virtio/virtio-pci.h b/hw/virtio/virtio-pci.h
>> index ffb74bb..aecd4eb 100644
>> --- a/hw/virtio/virtio-pci.h
>> +++ b/hw/virtio/virtio-pci.h
>> @@ -86,6 +86,12 @@ typedef struct VirtioBusClass VirtioPCIBusClass;
>>   #define VIRTIO_PCI_FLAG_MODERN_PIO_NOTIFY \
>>       (1 << VIRTIO_PCI_FLAG_MODERN_PIO_NOTIFY_BIT)
>>   
>> +/* Where vhost-user implementation exists, using the guest notifier mask
>> + * feature can lead to improper interrupt management. Add a flag to
>> + * allow to disable this guest notifier mask if desired */
>> +#define VIRTIO_PCI_FLAG_USE_NOTIFIERMASK_BIT 6
>> +#define VIRTIO_PCI_FLAG_USE_NOTIFIERMASK (1 << VIRTIO_PCI_FLAG_USE_NOTIFIERMASK_BIT)
>> +
>>   typedef struct {
>>       MSIMessage msg;
>>       int virq;
>> -- 
>> 2.1.4
>>