Messages in this thread | | | Subject | Re: [RFC PATCH] vdpa: mandate 1.0 device | From | Jason Wang <> | Date | Wed, 21 Apr 2021 15:41:36 +0800 |
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在 2021/4/12 下午5:23, Jason Wang 写道: > > 在 2021/4/12 下午5:09, Michael S. Tsirkin 写道: >> On Mon, Apr 12, 2021 at 02:35:07PM +0800, Jason Wang wrote: >>> 在 2021/4/10 上午12:04, Michael S. Tsirkin 写道: >>>> On Fri, Apr 09, 2021 at 12:47:55PM +0800, Jason Wang wrote: >>>>> 在 2021/4/8 下午11:59, Michael S. Tsirkin 写道: >>>>>> 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 ... >>>> My point is this neither fixes or prevents this. >>>> >>>> So my suggestion is to finally add ioctls along the lines >>>> of PROTOCOL_FEATURES of vhost-user. >>>> >>>> Then that one can have bits for legacy le, legacy be and modern. >>>> >>>> BTW I looked at vhost-user and it does not look like that >>>> has a solution for this problem either, right? >>> >>> Right. >>> >>> >>>> >>>>>> 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 >>>> I frankly think we'll need PROTOCOL_FEATURES anyway, it's too >>>> useful ... >>>> so why not teach drivers about it and be done with it? You can't >>>> emulate >>>> legacy on modern in a cross endian situation because of vring >>>> endian-ness ... >>> >>> So the problem still. This can only work when the hardware can support >>> legacy vring endian-ness. >>> >>> Consider: >>> >>> 1) the leagcy driver support is non-normative in the spec >>> 2) support a transitional device in the kenrel may requires the >>> hardware >>> support and a burden of kernel codes >>> >>> I'd rather simply drop the legacy driver support >> >> My point is this patch does not drop legacy support. It merely mandates >> modern support. > > > I am not sure I get here. This patch fails the set_feature if > VERSION_1 is not negotiated. This means: > > 1) vDPA presents a modern device instead of transitonal device > 2) legacy driver can't be probed > > What I'm missing?
Hi Michael:
Do you agree to find the way to present modern device? We need a conclusion to make the netlink API work to move forward.
Thanks
> > >> >>> to have a simple and easy >>> abstarction in the kenrel. For legacy driver in the guest, >>> hypervisor is in >>> charge of the mediation: >>> >>> 1) config space access endian conversion >>> 2) using shadow virtqueue to change the endian in the vring >>> >>> Thanks >> I'd like to avoid shadow virtqueue hacks if at all possible. >> Last I checked performance wasn't much better than just emulating >> virtio in software. > > > I think the legacy driver support is just a nice to have. Or do you > see any value to that? I guess for mellanox and intel, only modern > device is supported in the hardware. > > 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 >
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