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Date: Tue, 2 Mar 2021 18:53:50 +0800 From: Jason Wang <jasowang@...hat.com> To: "Michael S. Tsirkin" <mst@...hat.com> Cc: Si-Wei Liu <si-wei.liu@...cle.com>, elic@...dia.com, linux-kernel@...r.kernel.org, virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org Subject: Re: [PATCH] vdpa/mlx5: set_features should allow reset to zero On 2021/3/2 5:47 下午, Michael S. Tsirkin wrote: > On Mon, Mar 01, 2021 at 11:56:50AM +0800, Jason Wang wrote: >> On 2021/3/1 5:34 上午, Michael S. Tsirkin wrote: >>> On Wed, Feb 24, 2021 at 10:24:41AM -0800, Si-Wei Liu wrote: >>>>> Detecting it isn't enough though, we will need a new ioctl to notify >>>>> the kernel that it's a legacy guest. Ugh :( >>>> Well, although I think adding an ioctl is doable, may I know what the use >>>> case there will be for kernel to leverage such info directly? Is there a >>>> case QEMU can't do with dedicate ioctls later if there's indeed >>>> differentiation (legacy v.s. modern) needed? >>> BTW a good API could be >>> >>> #define VHOST_SET_ENDIAN _IOW(VHOST_VIRTIO, ?, int) >>> #define VHOST_GET_ENDIAN _IOW(VHOST_VIRTIO, ?, int) >>> >>> we did it per vring but maybe that was a mistake ... >> >> Actually, I wonder whether it's good time to just not support legacy driver >> for vDPA. Consider: >> >> 1) It's definition is no-normative >> 2) A lot of budren of codes >> >> So qemu can still present the legacy device since the config space or other >> stuffs that is presented by vhost-vDPA is not expected to be accessed by >> guest directly. Qemu can do the endian conversion when necessary in this >> case? >> >> Thanks >> > Overall I would be fine with this approach but we need to avoid breaking > working userspace, qemu releases with vdpa support are out there and > seem to work for people. Any changes need to take that into account > and document compatibility concerns. Agree, let me check. > I note that any hardware > implementation is already broken for legacy except on platforms with > strong ordering which might be helpful in reducing the scope. Yes. Thanks > >
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