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Subject: Re: [RFC PATCH] vdpa: mandate 1.0 device
To:     "Michael S. Tsirkin" <mst@redhat.com>
Cc:     virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org, parav@nvidia.com, elic@nvidia.com
References: <20210408082648.20145-1-jasowang@redhat.com>
 <20210408115834-mutt-send-email-mst@kernel.org>
From:   Jason Wang <jasowang@redhat.com>
Message-ID: <a6a4ab68-c958-7266-c67c-142960222b67@redhat.com>
Date:   Fri, 9 Apr 2021 12:47:55 +0800
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?? 2021/4/8 ????11:59, Michael S. Tsirkin д??:
> On Thu, Apr 08, 2021 at 04:26:48PM +0800, Jason Wang wrote:
>> This patch mandates 1.0 for vDPA devices. The goal is to have the
>> semantic of normative statement in the virtio spec and eliminate the
>> burden of transitional device for both vDPA bus and vDPA parent.
>>
>> uAPI seems fine since all the vDPA parent mandates
>> VIRTIO_F_ACCESS_PLATFORM which implies 1.0 devices.
>>
>> For legacy guests, it can still work since Qemu will mediate when
>> necessary (e.g doing the endian conversion).
>>
>> Signed-off-by: Jason Wang <jasowang@redhat.com>
> Hmm. If we do this, don't we still have a problem with
> legacy drivers which don't ack 1.0?


Yes, but it's not something that is introduced in this commit. The 
legacy driver never work ...


> Note 1.0 affects ring endianness which is not mediated in QEMU
> so QEMU can't pretend to device guest is 1.0.


Right, I plan to send patches to do mediation in the Qemu to unbreak 
legacy drivers.

Thanks


>
>
>
>
>
>> ---
>>   include/linux/vdpa.h | 6 ++++++
>>   1 file changed, 6 insertions(+)
>>
>> diff --git a/include/linux/vdpa.h b/include/linux/vdpa.h
>> index 0fefeb976877..cfde4ec999b4 100644
>> --- a/include/linux/vdpa.h
>> +++ b/include/linux/vdpa.h
>> @@ -6,6 +6,7 @@
>>   #include <linux/device.h>
>>   #include <linux/interrupt.h>
>>   #include <linux/vhost_iotlb.h>
>> +#include <uapi/linux/virtio_config.h>
>>   
>>   /**
>>    * vDPA callback definition.
>> @@ -317,6 +318,11 @@ static inline int vdpa_set_features(struct vdpa_device *vdev, u64 features)
>>   {
>>           const struct vdpa_config_ops *ops = vdev->config;
>>   
>> +        /* Mandating 1.0 to have semantics of normative statements in
>> +         * the spec. */
>> +        if (!(features & BIT_ULL(VIRTIO_F_VERSION_1)))
>> +		return -EINVAL;
>> +
>>   	vdev->features_valid = true;
>>           return ops->set_features(vdev, features);
>>   }
>> -- 
>> 2.25.1