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Date: Thu, 26 May 2022 10:57:03 +0200
From: Eugenio Perez Martin <eperezma@...hat.com>
To: "Dawar, Gautam" <gautam.dawar@....com>
Cc: "Michael S. Tsirkin" <mst@...hat.com>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
"virtualization@...ts.linux-foundation.org"
<virtualization@...ts.linux-foundation.org>,
Jason Wang <jasowang@...hat.com>,
Zhu Lingshan <lingshan.zhu@...el.com>,
"martinh@...inx.com" <martinh@...inx.com>,
Stefano Garzarella <sgarzare@...hat.com>,
"ecree.xilinx@...il.com" <ecree.xilinx@...il.com>,
Eli Cohen <elic@...dia.com>,
Dan Carpenter <dan.carpenter@...cle.com>,
Parav Pandit <parav@...dia.com>,
Wu Zongyong <wuzongyong@...ux.alibaba.com>,
"dinang@...inx.com" <dinang@...inx.com>,
Christophe JAILLET <christophe.jaillet@...adoo.fr>,
Xie Yongji <xieyongji@...edance.com>,
"lulu@...hat.com" <lulu@...hat.com>,
"martinpo@...inx.com" <martinpo@...inx.com>,
"pabloc@...inx.com" <pabloc@...inx.com>,
Longpeng <longpeng2@...wei.com>,
"Piotr.Uminski@...el.com" <Piotr.Uminski@...el.com>,
"Kamde, Tanuj" <tanuj.kamde@....com>,
Si-Wei Liu <si-wei.liu@...cle.com>,
"habetsm.xilinx@...il.com" <habetsm.xilinx@...il.com>,
"lvivier@...hat.com" <lvivier@...hat.com>,
Zhang Min <zhang.min9@....com.cn>,
"hanand@...inx.com" <hanand@...inx.com>
Subject: Re: [PATCH v3 2/4] vhost-vdpa: introduce STOP backend feature bit
On Wed, May 25, 2022 at 1:23 PM Dawar, Gautam <gautam.dawar@....com> wrote:
>
> [AMD Official Use Only - General]
>
> -----Original Message-----
> From: Eugenio Pérez <eperezma@...hat.com>
> Sent: Wednesday, May 25, 2022 4:29 PM
> To: Michael S. Tsirkin <mst@...hat.com>; netdev@...r.kernel.org; linux-kernel@...r.kernel.org; kvm@...r.kernel.org; virtualization@...ts.linux-foundation.org; Jason Wang <jasowang@...hat.com>
> Cc: Zhu Lingshan <lingshan.zhu@...el.com>; martinh@...inx.com; Stefano Garzarella <sgarzare@...hat.com>; ecree.xilinx@...il.com; Eli Cohen <elic@...dia.com>; Dan Carpenter <dan.carpenter@...cle.com>; Parav Pandit <parav@...dia.com>; Wu Zongyong <wuzongyong@...ux.alibaba.com>; dinang@...inx.com; Christophe JAILLET <christophe.jaillet@...adoo.fr>; Xie Yongji <xieyongji@...edance.com>; Dawar, Gautam <gautam.dawar@....com>; lulu@...hat.com; martinpo@...inx.com; pabloc@...inx.com; Longpeng <longpeng2@...wei.com>; Piotr.Uminski@...el.com; Kamde, Tanuj <tanuj.kamde@....com>; Si-Wei Liu <si-wei.liu@...cle.com>; habetsm.xilinx@...il.com; lvivier@...hat.com; Zhang Min <zhang.min9@....com.cn>; hanand@...inx.com
> Subject: [PATCH v3 2/4] vhost-vdpa: introduce STOP backend feature bit
>
> [CAUTION: External Email]
>
> Userland knows if it can stop the device or not by checking this feature bit.
>
> It's only offered if the vdpa driver backend implements the stop() operation callback, and try to set it if the backend does not offer that callback is an error.
>
> Signed-off-by: Eugenio Pérez <eperezma@...hat.com>
> ---
> drivers/vhost/vdpa.c | 16 +++++++++++++++-
> include/uapi/linux/vhost_types.h | 2 ++
> 2 files changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c index 1f1d1c425573..32713db5831d 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -347,6 +347,14 @@ static long vhost_vdpa_set_config(struct vhost_vdpa *v,
> return 0;
> }
>
> +static bool vhost_vdpa_can_stop(const struct vhost_vdpa *v) {
> + struct vdpa_device *vdpa = v->vdpa;
> + const struct vdpa_config_ops *ops = vdpa->config;
> +
> + return ops->stop;
> [GD>>] Would it be better to explicitly return a bool to match the return type?
I'm not sure about the kernel code style regarding that casting. Maybe
it's better to return !!ops->stop here. The macros likely and unlikely
do that.
Thanks!
> +}
> +
> static long vhost_vdpa_get_features(struct vhost_vdpa *v, u64 __user *featurep) {
> struct vdpa_device *vdpa = v->vdpa; @@ -575,7 +583,11 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
> if (cmd == VHOST_SET_BACKEND_FEATURES) {
> if (copy_from_user(&features, featurep, sizeof(features)))
> return -EFAULT;
> - if (features & ~VHOST_VDPA_BACKEND_FEATURES)
> + if (features & ~(VHOST_VDPA_BACKEND_FEATURES |
> + BIT_ULL(VHOST_BACKEND_F_STOP)))
> + return -EOPNOTSUPP;
> + if ((features & BIT_ULL(VHOST_BACKEND_F_STOP)) &&
> + !vhost_vdpa_can_stop(v))
> return -EOPNOTSUPP;
> vhost_set_backend_features(&v->vdev, features);
> return 0;
> @@ -624,6 +636,8 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
> break;
> case VHOST_GET_BACKEND_FEATURES:
> features = VHOST_VDPA_BACKEND_FEATURES;
> + if (vhost_vdpa_can_stop(v))
> + features |= BIT_ULL(VHOST_BACKEND_F_STOP);
> if (copy_to_user(featurep, &features, sizeof(features)))
> r = -EFAULT;
> break;
> diff --git a/include/uapi/linux/vhost_types.h b/include/uapi/linux/vhost_types.h
> index 634cee485abb..2758e665791b 100644
> --- a/include/uapi/linux/vhost_types.h
> +++ b/include/uapi/linux/vhost_types.h
> @@ -161,5 +161,7 @@ struct vhost_vdpa_iova_range {
> * message
> */
> #define VHOST_BACKEND_F_IOTLB_ASID 0x3
> +/* Stop device from processing virtqueue buffers */ #define
> +VHOST_BACKEND_F_STOP 0x4
>
> #endif
> --
> 2.27.0
>
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