Re: [PATCH v1 1/4] virtio: protect non-modern devices from too big virtqueue size setting

[Denis Plotnikov <dplotnikov@virtuozzo.com>]

On 05.11.2019 23:56, Michael S. Tsirkin wrote:
> On Tue, Nov 05, 2019 at 07:11:02PM +0300, Denis Plotnikov wrote:
>> The patch protects from creating illegal virtio device configuration
>> via direct virtqueue size property setting.
>>
>> Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
>> ---
>>   hw/virtio/virtio-blk-pci.c  |  9 +++++++++
>>   hw/virtio/virtio-scsi-pci.c | 10 ++++++++++
>>   2 files changed, 19 insertions(+)
>>
>> diff --git a/hw/virtio/virtio-blk-pci.c b/hw/virtio/virtio-blk-pci.c
>> index 60c9185c39..6177ff1df8 100644
>> --- a/hw/virtio/virtio-blk-pci.c
>> +++ b/hw/virtio/virtio-blk-pci.c
>> @@ -48,6 +48,15 @@ static void virtio_blk_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
>>   {
>>       VirtIOBlkPCI *dev = VIRTIO_BLK_PCI(vpci_dev);
>>       DeviceState *vdev = DEVICE(&dev->vdev);
>> +    bool modern = virtio_pci_modern(vpci_dev);
>> +    uint32_t queue_size = dev->vdev.conf.queue_size;
>> +
>> +    if (!modern && queue_size > 128) {
>> +        error_setg(errp,
>> +                   "too big queue size (%u, max: 128) "
>> +                   "for non-modern virtio device", queue_size);
>> +        return;
>> +    }
>
> this enables for transitional so still visible to legacy
> interface. I am guessing you want to check whether
> device is accessed through the modern interface instead.

My goal is to not break something when I'm setting the queue size > 128 
(taking into account the current seabios queue size restriction to 128). 
I'm not quite sure what to check. Could I ask why one want to the check 
whether accessing through the modern interface and how it could be checked?

Thanks!

Denis

>>       if (vpci_dev->nvectors == DEV_NVECTORS_UNSPECIFIED) {
>>           vpci_dev->nvectors = dev->vdev.conf.num_queues + 1;
>> diff --git a/hw/virtio/virtio-scsi-pci.c b/hw/virtio/virtio-scsi-pci.c
>> index 2830849729..6e6790fda5 100644
>> --- a/hw/virtio/virtio-scsi-pci.c
>> +++ b/hw/virtio/virtio-scsi-pci.c
>> @@ -17,6 +17,7 @@
>>   
>>   #include "hw/virtio/virtio-scsi.h"
>>   #include "virtio-pci.h"
>> +#include "qapi/error.h"
>>   
>>   typedef struct VirtIOSCSIPCI VirtIOSCSIPCI;
>>   
>> @@ -47,6 +48,15 @@ static void virtio_scsi_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
>>       VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(vdev);
>>       DeviceState *proxy = DEVICE(vpci_dev);
>>       char *bus_name;
>> +    bool modern = virtio_pci_modern(vpci_dev);
>> +    uint32_t virtqueue_size = vs->conf.virtqueue_size;
>> +
>> +    if (!modern && virtqueue_size > 128) {
>> +        error_setg(errp,
>> +                   "too big virtqueue size (%u, max: 128) "
>> +                   "for non-modern virtio device", virtqueue_size);
>> +        return;
>> +    }
> why? what is illegal about 256 for legacy?
>
>>   
>>       if (vpci_dev->nvectors == DEV_NVECTORS_UNSPECIFIED) {
>>           vpci_dev->nvectors = vs->conf.num_queues + 3;
>> -- 
>> 2.17.0